Exhaust Port Dyno Test At 203° - Will It Work? 100mph Moped Challenge
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- Опубліковано 11 лис 2023
- Today I do some testing of raising the exhaust port on my Kawasaki AR 50 with an Autisa big bore kit (93cc) to see if some more power can be gained.
I'm kinda going outside of the recommended timings as illustrated here by Alex on 2 Stroke Stuffing: • HIGHER EXHAUST PORT, G... - Авто та транспорт
Thank you to all who took the time to chat in the Premier - It was really cool getting to chat with you all and getting tips and suggestions - thank you.
A quick n dirty way of experimenting with port timing is to take down the edge of the piston crown.. old 70s tricks.. its not a "race" solution but does give fiddle room to see when power band gets too radical without risking the barrel.. dont go past half height ring to crown lip.. or youll cook the top ring.. pistons are cheap.. lengthen your pipe too for the extended timing
Look for a book.. 2-stroke performance tuning , A Graham Bell.. looove double knockers
id like to see him do that with his dykes ring....@@Errol.C-nz
Errol, what Aljaxon69 said 🙂
@@aljaxon69 yeah na won't work with them BUT.. they're not a performance fitment especially on loop scavenged 2-strokes.. too heavy & draggy.. great on uniflo & high torque tune
Errol, this was my plan as I've done it before but as mentioned by others the dykes L ring sits virtually at the piston crown so I can't,
love the video, 2 stroke dyno tuning content is hard to come by, love to see more
Hi, well you've come to the right place. I've plenty more Dyno tuning planned. 😃
Really good gains from raising the exhaust port, with these small capacity two strokes every tiny modification matters.
I've no doubt you will see extra power with the exhaust sealed up and regaining backpressure and further gains when optimising ignition timing and jetting.
Looking forward to the next video!!!
Cheers and hopefully a little more power next time. I normally get a good deal on the sliding belly but not this time.
@@AutoBeta2T great work! i love these kinds of videos!
I would love to see if polishing up that port would also bring some smoother HP.
And maybe also chamfering/deburring that inner side of the exhaust port so that the piston rings glide over more easily
@InFlamesOfSorrow cheers buddy.
Yes the port polishing is on the list of things to try (it's getting quite long now) so hopefully in the new year I'll get around to trying it.
Good progress! Moving along nicely!
Thank you Impuls ☺️
One thing that may be worth trying, UA-camr @ASoftaaja removed the lower ring and made HP gains from that alone. At these RPMs, any friction reduction = power gains. 2stroke stuffing also came to the same conclusion (not the rings, but any drag in the engine at this speeds robs HP). Running more oil has also proven gains for the same reason (tech document published by Kawasaki ~30yrs ago - though oil tech may have caught up enough to make that moot)
Great info. I'll put it on the list to try next time. Loosing the lower ring would allow a wider inlet port too as the lower ring peg is perilously close to the edge of the intake window.
Thumbs up for that! Both of those are indeed well proven methods to get some pretty much free power.
If I recall correctly the threshold where one piston ring starts to outperform two tends to be around 8000rpm quite universally so one ring will very likely perform better for this project.
About oil mix there is at least one document from 70's or 80's where they tested with some 250 mx bike and castor oil. Tested ratios were 15:1, 20:1 and 30:1. Compared to 20:1 the 30:1 ratio reduced power by 10% (!) while 15:1 increased it by 1.5%. Their main hypothesis was that power increase from more oil would be from improved sealing between piston(ring) and cylinder. The results can for sure vary depending on many factors, especially piston/cylinder clearances and used oil type. Would be interesting to see this tested with various modern oils. One important safety note though when using premix: More oil makes the air-fuel mix leaner by making the fuel heavier/thicker, so increasing jet size might be needed even though common sense could easily suggest the opposite.
Oil also reduces the octane rating of the fuel, so if you are running on the bleeding edge of detonation a higher oil premix ratio might cause knocking even with the mixture unchanged.
@nerd1000ify interesting - I need to do some more reading into oil ratios. Cheers
More oil makes it leaner too, leaner usually makes more top end power. So that needs to be into consideration. So jetting should be different, at least at the extreme ends of it.
I'd love to see this project progress! I actually found this channel from the sidebar recommendations while watching 2Stroke Stuffing.
Subbed!
Thanks for the sub :)
It's good to hear the algorithm is associating me with 2 Stroke Stuffing... It's a strange beast - I've been recommended against some very odd videos as it tried to figure out my target audience. Probably not helped by me going off topic a few times and not really uploading this year.
Nice to have you on board and I hope you enjoy future episodes (and some of my older ones).
This is the sort of channel I’ve been looking for. Great stuff keep it up 👍
Pleased you have found it. And thanks for the comment as it keeps motivation up. More coming soon :)
just found you, im hooked. no crap just fact. no crap music. you are very clear on what you are doing
Cheers John, I'm pleased you are enjoying. Note. There is some crap music in some of my other vids... Not too much I hope.
I do try to convey the facts though. Good or bad results 😊
Really impressive gains! Keep it up!
Streetwise, cheers and I will.
Only just found your site, very interesting.
Look forward to watching a lot more. Thanks.
Hi Jack, I'm pleased you are enjoying it.
Lots more coming up soon hopefully 😀
Love those dyno comparisons!!
Glad you like them and there will be more to come. Cheers for watching :)
Thank you, that was perfect.
Great information!
Cheers Randell. Thanks for watching
Very cool tests
Cheers, I hope they help.
One of the best 2t channel that i love .
Thank you 😄
You're going in the right direction by using a larger radius on the top of port to ease ring back into cylinder. On the RD375's, I raised the port to 196 deg, but the engine was working at a lower rpm and couldn't make use of the higher rpm. But one thing I did do to help blow down was make the port much wider at edges. Think of a trapezoid with the wider part at top of port, and narrower part at BDC. The edges of the exhaust port on the RD/RZ's would overlap the front edge of transfer port for about 72% width, or about 48mm on a 66mm bore.. This helped get the gasses out without the need for a higher port, helping powerband. The widest part of the port was only about 5mm, so inertia kept the rings in place without jumping into the port. It added 500 RPM to top for a power band of 6k to 9k.
Awesome work and well made video.
Cheers Ross, thanks for the feedback 😄
Some big gains there mate.
Cheers Jim. I thought I needed to get my finger out to reduce the risk of you unsubscribing 😉
Keep up the good work 😊
Will do Trevor 😀 thanks for watching ☺️
great job again lad hp is creeping up keep up the good work
Thank you Mark. We are getting there 💪
love your content
Cheers Stanley 🙂
This is brilliant, back in the late 80's, my first girlfriend had an AR 50 and an AR 80. I did exactly the same to the 80 ( 93 barrel tuned, micron pipe and a slightly bigger carb) , it would wheelie off the throttle in second gear ( and third with a bit of help ). It was more fun to ride than my RDLC because of the power to weigh ratio.
Ah the good old days 👍
I will be following this closely, keep up the good work 👍👍
Hi Stephen - if she rode an AR 50 and an 80 she sounded like a keeper!
Yep, these are lots of fun. I took it out last year before I did most of the mods and it loved popping up the front wheel in second - lots of giggles :)
And thanks for tuning in, cheers, Dave
Nice video, the step by step porting / dyno runs was fun to watch....... was getting nervous for you ....... when to call good enough! lol
Cheers, and yes, I think I stopped at the right point. I may be able to get a little more area from flattening the roof and widening a smidge.
Love your work. I envy your access to a dyno.
Changing exhaust timing will change the required tuned length of the pipe. At this stage I'd be looking at the pipe length and jetting. I think it was Bell who said "choose your porting and then tune it with the pipe".
I use Fritz Overmars' method of checking when the port is classed as 'open', using the 0.7mm bent wire. It gives consistency.
Have you delved into the specific time areas yet?
Hi Rob,
Yes a new pipe at some point but in my case I think I was getting the exhaust port aligned to what the pipe wanted. I had to move the ignition curve to the right 2000rpm too.
I used Frits' method to measure the ports which is where I think I had an issue as the dykes ring piston doesn't control the port opening - it appears to be the ring as the top of the piston is a smaller diameter that the rest of the piston to accommodate the L shaped ring. I need to double check again though.
I have had great results spacing up the cylinder, that way the transfer duration and flow area increases, it works very well when you are increasing the peak HP RPM, I would try 1-2mm spacers on a cylinder with the stock exhaust port height, machine the spacer thickness off the top of the cylinder, just make sure the bottom ring end gap doesn't pop out into the intake port @ BDC. I would space up a cylinder first before any porting when you want the peak HP RPM higher. In my experience a1mm spacer was good for about 1000rpm increase in peak HP RPM on a 120cc engine without any porting, cut the piston skirt on the intake side on a piston port engine. *You will have to grind the bottoms of the transfers and exhaust port after spacing the cylinder if the port bottoms are above the pistons. I have spaced cylinders up to 3mm, that moved peak power RPM from 7200 to 9500rpm on a 600cc triple snowmobile engine.
Hi, I'm a bit stuck with the current cylinder as the barrel can't go much higher as the piston will pop out of the top and with the dykes ring sitting 0.5 mm below the crown of the piston i'm a bit stuck. I did do a quick test before the last raise of the exhaust port and it didn't make anymore power unfortunately but that could have been compression loss.
I do like the idea of a spacer to increase the transfer duct inlet area. I could do this by installing the 5mm loger rod I have (RM80)!???
Thanks for all the info and ideas - appreciated.
You can measure when the exhaust opens by running compressed air into the plug hole and then rotating until you see a pressure drop.
Crackin' series
Thank you Sam 😊
Awesome mate, I own an RS50, get 65 stock. Love these AR50’s!!
I used to race a RS50 - brilliant little bike and quick too! What mods are on yours?
16:30 I don't know how you will flow test the ex but I can tell you that a flow bench will only give valid figures for the tested conditions but the running conditions are totally different. The pressures are much higher, the temperature is much higher (which means the speed of sound and viscosity of the gas is much higher). In running conditions it can have choked flow which the flow bench won't duplicate.
The flow bench will give some thought provoking info but don't bank on it because it can be totally wrong.
Happy to subscribe.
Hi Alan, happy to have you for the journey - hopefully we get to 100 MPH :)
Cheers for subbing and welcome 😃
Back in my days of dirt, bikes and motocross (1976)we used to cut the intake skirt shorter on the piston 10 mm.
Cheers, my piston has windows so I'm not able too. However, with a different piston...
This is where an exhaust power valve would pay big dividends.
Agreed 🙂
If only it did 😭
Great video. What kind of ignition are you running? As you know ignition timing is a major factor for gaining power. I saw that you have quite a bit of wet mixture on top of your piston, so maybe the ignition is set a bit on the late side?
Nice video didnt think raising the port would give you that much
Cheers ans me either. Just 0.5mm made quite a difference!
Awesome video! I was hoping that you would have done a compression check every time you raised the exhaust port. Im curious about how much the compression decreases. With that said every time you raise the exhaust port you should increase compression ratio via head gasket thickness, the idea being to keep the compression the same throughout the test. I imagine you would have even more horsepower 👍
Cheers Baby Shark! I have some new heads that I will cut to get the trapped compression back (this will increase the geometric compression. Prior to raising the geometric compression was 13.8:1 and the corrected was 7.4:1. After raising the port the corrected lowered to 7:1. I'm keen to test this. Stay tuned :)
Very good video, no bullshit and perfect approach to mods, had to subscribe. Can you make the same video but raising all the Port timings by putting a thicker gasket (+0.5mm) and embedding the head to keep the same compression ratio? That would be awesome
Thanks Riccardo. I did try raising the barrel with a 0.4mm gasket before the final exhaust port grind but lost power. Maybe that was because the compression dropped? Because of how the head fits it's a bit tricky to adjust the compression.
I would like to make a skull cap with interchangeable domes. This would allow to do what you are describing.
Definitely spend the time making skull caps, as this will give you time to build in squish variables too
That's the plan. However, I've brought a load of AR50 heads off ebay and plan to try different squish and CR with them.
OK and FWIW, I’d mod the worst one AR50 head, especially if you access to a lathe, some good quality aluminium stock, but it’s your baby :)
@mikecrane2782 the standard castings are generally not too bad. I do have a TS100 head (the same as used in the original project) that I planned to use with inserts (it has a lot more mass than a AR head). Like a lot.of this it's finding the time at the min.
What grade of aluminium would you recommend for head inserts?
A couple of us did some radical stuff on yamaha fs-1e's in the late early 80's. drastic disc valve mods to increase inlet duration and some pretty wild porting and skimming heads. and we used "Castrol R" racing vegetable oil on some of the more higher revving ones which stopped them seizing. a very small finned IRON barrel gets very hot and cannot dissipate the heat .
What sort of speeds did you get? Sounds fun!
@@AutoBeta2T around 55-60 mph sat upright on the flat in calm conditions. we did achieve 65mph prone on the flat on one of them but the rev limit was so high and the power band so narrow it was geared Down 2 teeth at the gearbox sprocket to be able to use to top gear around town. on that one it must have been revving to 12000+ rpm and difficult to ride !
Brilliant 😊
Now this is how you do research. I think you should also be looking at the area of the port. Shape, size, and timing each make a difference. Each part of the air flow needs to match the flow before it and after it. Being the flow of the Intake, intake port, transfers, exhaust, and pipe.
Hi David - agreed but it's quite a task. I'm hopefully doing some flow testing this weekend. Hopefully that will give some pointers.
more ig timing will likely also help - but it's more a bandaid to helping the pipe tuned length
Hi Derek, more ignition timing is the next video... Possibly too much!
I watched your 2 stroke ignition video the other day - great info and got me thinking about the subject. Cheers.
Really good video, you got some good gains there and a nice careful approach so that you did not wreck the barrel. You may consider the following either a 'cheat-to-far' or too expensive but you could possibly fit a 6 speed box from the AR80 assuming it will fit. I did something similar with my MT5, It was a pain with the 5 speed box, I would rev the nuts off it in fourth but even then it would more or less fall out of the powerband when I shifted up to 5th, it took ages to climb back into the powerband and then it would start pulling well. The six speed box from an MTX80 really helped me keep the engine buzzing. Of course a 6 speed box won't give you a higher top speed but it helps you get to that top speed a bit quicker especially if conditions are not perfect.
EDIT Just did a bit of googling, the AR50 was 6 speed in other countries, I wonder if Kawasaki just fitted a gear selector cam on the UK bikes that only allows 5 gears to be selected even though the 6th gear is actually in the box, it would be like Christmas if that is the case! (You can just grind the selector plate to allow the extra gear to be selected)
Hi Pete, cheers but I already have the 6 speed box, I bought the extra bits from the AR80 box. In fact I had to get a couple of bits from the US.
@@AutoBeta2T LOL, well it proves that great minds think alike! 🙂
nice job
Thank you Marius :)
I personally like to have a peek in my exhaust port for the exact reason you’re saying it definitely gives us more longevity now mind you I build for reliability and power as a secondary I ride daily motorized bicycles as you can see in my channel name so when I’m building for power I definitely tend to keep a flatter roof but in anything that I’m gonna ride every day get on ride it hard I will keep a flatter overall roof With a very small taper. I just found your channel today in my feed and I like the video it was enjoyable look forward to seeing more and you hitting your hundred mile an hour goal
Cheers for the Info JMB, I'll look to flattening the roof again. And cheers - hopefully we'll get there next year - 100MPH!
Transfer work will widen the spread of power now. Add 2deg transfer duration to fatten the curve and add some more peak.
Cheers, I plan to do some transfer tests
2 degrees would be a half mil height change or thereabouts?
Yes, there abouts. I'd have to check to be sure.
Just subbed. I´ve been really getting into these moped wars. Asoftaaja, Two Stroke Stuffing and now you. And seems like you are leading the race
Cheers PPekka :) Asoftaaja has just had a good breakthrough with ignition. Plus I'm at 97 cc!
@@AutoBeta2T oh. I thought you were doing 50cc too. Well not Bad still, not going to unsub for that 😅
Cheers - I do have to contend with air-cooling, a very over square engine, rubbish transfer ducts and a single exhaust port. 🙃
When using a dyno corrected vs uncorrected doesn’t really matter as long as you use the same option on all runs, I like using uncorrected because I feel like it lets you see what the engine is doing compared to current weather conditions which allows you to see when the engine is really not happy with conditions, if it’s 100 degrees f outside and the engine loses a major amount of power compared the corrected figure you need to change jetting and timing to keep it alive in those hot temperatures
Cheers for the info buddy. That's a really good point and something I hadn't considered. I guess it's a bit like going to the track and changing jetting to compensate for the changes in the local conditions. Cheers :)
@@AutoBeta2T yep it gives you an idea of what the motor actually needs some motors will take more heat than others before the fuel mixture needs to be enriched.most of my 2 stroke knowledge comes from chainsaws which are used in many altitudes and temperatures and sometimes it’s not all about air density, temperature, humidity and barometric pressure all effect engines differently.
Close to 2000 now! 🎉😊
Yep, getting there. Cheers Johnny.
new here/. Love 2t tuning! subbscribed
Welcome BEYTEK 😁
one thing I have not seen mentioned is the extra stress on the ring locating pins. If your ex port mods are not perfectly symmetrical the side load will loosen the pin with very sad results. I found that out unfortunately.
On a port with rounded edges I measure to where the curved port edge is 45 degrees from vertical.
Raising the exhaust port allows more blowdown time for less exhaust pressure overlap of the transfers at high RPM for less restricted transfer flow which increases power but at the same time lowers the trapped cc so it is possible to raise it too high.
Yes, increasing blowdown certainly seemed to help on this engine. I believe it still may want a little more, particularly with the new pipe mick abbey had that gave a flat top to the power curve peak. For the final test, I only raised the centre of the exhaust roof so it could be flattened a bit more. I have heard of durations as high as 208 degrees on the exhaust duration on single port exhausts... I guess a trade-off between slowdown area and trapped compression.
Then again, lowering compression can put more energy into the pipe...
As with all things, two stroke: change one thing a affect several others!
Great stuff.
I like it when people share info like I do. We are all in it to have fun and learn.
I'm subscribed to you and twostrokestuffing even though I'm not a 50cc guy. It's just that you guys share info.
I did a test and posted it on my channel about exhaust back pressure.
I hooked up a pressure,vacuum gauge to my exhaust pipe on one of my Honda FL350's.
With the stock exhaust and muffler it has 3.5 psi back pressure and without the muffler it had 2 psi back pressure.
These runs were done at my local airport side road and not on a dyno so I have no idea about any hp gains or losses.
I did it just to see how much back pressure was in the exhaust system of a two stroke.
Could you do a dyno video on hp with regards to exhaust back pressure one day ??
Thx for any replies.
Hi mate, no problems, it's what YT is all about for me 😃
I'll check out your video as pressure would be interesting to monitor particularly with changeable stinger inserts.
Gone from 196 to 203 degrees is what i use on my bike with an derbi ebs engine malossi mhr replica cylinder and it works wonders in making it live on high rpm, low down is no problem as the hebo bufanda without the extention stinger before silencer gives reasonable down low and up on topp
Extec, great to hear this timing works on other engines. Low end isn't a massive concern for me either... As long as I can get it on pipe and moving I should be good for the top speed runs.
@@AutoBeta2T mine is dynoed to 17.7hp depending on gearing top speed above 100km/h with my normal gearing 13/53 and posible to add 2-3 teeth on front for more speed.
Last time i changed piston where spring of 2010 and used the bike extensively for race track, street fun and for a while transport to work, stol got almost the same compression as it had new.
4% oil at all time.
The critical part is geting enough compression when rasing the exhaust port and get the blowdown timing right as when its to low or high it tends in both scenario to make the engine feel empty of power but more so on torque
Thanks for the info Extec :)
Trippy ,had an Ar50 with the same kit on in the late 80s 😅🤠🇬🇧🤟🙏
Great bikes - loved mine when I was 16 😀
@@AutoBeta2T Mine had a beautiful pair of Dunlop K series tyres on her ,she'd lay near flat round a bend, excellent handing, only the wiring was nasty and the kick-starts always snap 🤣🤠🙏🇬🇧 awesome little bikes 🛵🤟
@ianmangham4570 super sticky tyres then!
@@AutoBeta2T I bought her soon as I seen the new tyres ,the rest was a complete mess 🤠, I soon minted it and ended up selling her with a ar80 motor 🙏 ,great days great memories 🇬🇧 ,I miss her and my rd50m in that burgundy red ,and my suzuki gp's 100/125 ,but most of all I miss my mint condition suzy pe175 on a A plate ,that bike was so tough and beefy 🤠🇬🇧✌ use to vibrate a speedo to death at least once a month .
You have to think from the perspective of the gases inside the cylinder and to them the port is open ass soon as theres a tiny bit of light coming thru, as soon as there is a tiny hole the gases will start flowing out the port.
Agreed 👍
Back in the day…..
Autisa 93cc Barrel and piston
AR80 6 speed bottom end
Ar50 cylinder head, welded and turned to match
Exhaust side of the piston 2 small 1/8th holes drilled to match where the studs travel through the barrel, preventing hot spots.
No real porting just removing casting imperfections and polishing.
All speed exhaust
BDK race engineering CDI
Reed valve block spacer
I forget the sprocket sizes I used
But I reliable 85mph machine.
24mm carb
Castrol R and 4star petrol!
Sweet - sounds like a good spec. Mine would only go about 70 mph... I like 2 small holes in the piston trick. Not thought of that - cheers :)
Great work ! I recon with a new set of sprockets you'd be there at 100mph
I can't for the life of me remember what sprocket I ran on the back of mine but it was a lot smaller than standard.
Hi Trevor, that's one for a later episode at some point. I did have a work out but it's getting everything to clear with a bigger front and a smaller rear.
I'll see if I have any old photo's of my AR to try and gett an idea of size ;) @@AutoBeta2T
Cheers Trevor - my email is: Autobeta555@yahoo.com
About port-timing/angle, i use the caliper methode. More importent than the final angle, is the relative angle in comparison to the transfers.
So if you measure the transfers at 130° and the main port at 203°, the blowdown wil be 36,5°. Shifting the cilinder height doesn't change that number to much
Also i use the caliper to find piston-edge (dykes-ring edges) to cilinder-edge when piston is at BDC and calculate the port heights .
From 195°/203° you should see a drop in torque but a larger shift towards higher rpm (more hp). But at a certain moment only torque drops and there is no gain, this however only happens if the exhaust hasn't got a strong pressent in the first place.
Ps. I would also use a second piston with a lower compression height to exceed the 203° and the use for interim values.
Cheers for the tips.
I've not paid much attention to blowdown angle to be honest (more Blowdown STA). I have 36 degrees blowdown angle currently - is that a good figure? I imagine it is somewhere near the upper limits?
"35° is the longest period for most racers. Don't go too far.
130° for 'A' ports and 132° for 'B' and 'C' ports.
190° for 50cc engines and 198° for 125cc engines.
Maintain an equal exhaust-port angle*area to that of the intake, but never decrease the exhaust below 190°. Also, ensure that the angle*area of the blowdown remains approximately 13% of the transfers angle*area.
When blowdown is enlarged, transfers start to discharge better to the low-pressure cylinder. The same effect can be achieved by raising the transfers and blowdown proportionally, resulting in a much lower total exhaust duration."@@AutoBeta2T
You should consider running with the Dykes ring only.
I also lowered my AR50 as much as possible to cut drag and I turned the stearing triangle upside down to lower the handlebars.
Will do. It's been mentioned in another comment so keen to try it. Cheers 😀
Nice increase Dave, you're gonna hate me for saying this but might be worth seeing if the computer comes up with a different pipe design now that the blow down seems pretty much ok
Cheers and yes, I will certainly have to do another pipe for this... But first I have a few other experiments to conduct. But a pipe is on the list of things-to-do.
It will be interesting to see a new pipe with proper tuned length to now cylinder port duration
I'll be doing some tests again on pipe length at some point. I think a better pipe design could be found. Hopefully I'll find it.
You can retrieve some of that mid-range loss by going to a fatter (larger major diameter) pipe. It will make the engine more tractable.
I can remember mr Taylor telling me that a kx100 non pv as got potential of doing 100mph and he certainly didn’t hold back in telling me he’s certainly full of knowledge and a humble chap
Yep, Darrell is really knowledgeable and has a lot of experience. Really lucky to know him. 😄
@@AutoBeta2T what he don’t know isn’t worth knowing, forms temporary class is permanent 👌
there is a special caliper for marking scribing and stuff generally marking things that you want to cut etc it works perfect for 2 stroke port heights but you solution for that is definetly cheaper 😸
Hi Maciejz - do you have a link?
Best UA-cam Channel ever, please tune a cr250
Thanks Oliver. I am thinking about ideas for the next project ☺️
Great video have had some development in the past with ar 50 80 engines and the bdk wasnt impressive think a couple tweaks made 17hp from 14 but then development stoped as the guy was a busy man as were we
Cool, sounds like you were about where I am now. Were you running the BDK pipe and ignition?
Kx85 pipe made to fit underslung exhaust port was 192° you need to make your exhaust stub bigger so u have a step on your duct outlet for a disruption on the revered pulse should pick 1-2 hp up there
Hi again, thanks for the info.
My outlet is currently 30mm at the end of the stub but 32.7 mm at the outlet of the duct. I want to play with a stepped design. It appears to work well in the sim. I haven't tested in reality but it's good to hear you have found power from the step.
Cheers.
Ps. What was the diameter of the header inlet on the KX pipe?
Pipe wise i couldnt say as we had a kx pipe nikkon pipe and another the customer had to try
Yes make the stub bigger than the duct it will perform better
We mainly done exhaust port and intake porting
Bdk porting was not good
Think we gave it the 10 mins tune lol but then the bloke wanted to try the thai import cylinders ect
It ran a selletra rotor ignition kx85 pipe and a 30mn pwk
Try to keep your exhaust port roof as flat as possible with a nice radious this will give you more blowdown area what chord width are you on 70%? Also the stock duct is large anyway so i wouldnt go making it bigger or you will loose velocity in the blowdown phase
Had an AR50 back in the day. Did nearly 70mph on av gas alone. Good old 6 star juice. Hehe
Cool! I remember my dad running his bike on 2 star before they got rid of it. And it was super cheap!
You are leaving power on the table. The intake ports need to be smooth with no mismatch between intake manifold, gaskets, cylinder and liner. The transfer port also need to be smooth with no mismatch between casting, gasket (between cylinder and cases) and cylinder liner. The exhaust port needs a mirror finish with no mismatch between... Only mirror polish the exhaust port, do not mirror the transfers or intake. Just this alone could be good for 3-10% more power. Oh, and the exhaust pipe needs to be tuned to the port timings. There should be 2 stroke exhaust tuning guides to help with the pipe dimensions on the Internet. And be careful that the ports are well rounded in the corners so you do not snag the ring in the port. Basically the wider the port the more rounding you need in the corners. There should also be Internet pages to help with this too.
Higher compression will help a lot with HP however you risk burning up the engine if not careful.
A larger carburetor will help with top end and likely kill the bottom end power.
You can make two exhaust pipes one for high HP and one for max torque with a flat power band. I did this on a high HP cylinder that gave it a nice flat power band for riding in the woods.
Hi John, thanks for the info. You are the second person to mention the polishing of the exhaust duct and I'm keen to try that at some stage. I'm only after speed so as long as the powerband is wide toughen to pull all the gears (plus a bit for granny) I'll be happy :)
Hey mate great work and luv your dyno overlays definite thumbs up , however John is exactly right mate in regards to Port finishes and mismatches and this is where i,m super fussy ,and rounding ports and single ring . My sons and I run dirtkart with twin 100 yams , I rebuild and port all ours using above methods with great results i use a thin feeler guage in ports and degree wheel ( mainly for repeatability)though as direct drive I can't go too radical with exhaust timing or we loose to much bottom end and I also cut the head and tighten squish as tight as I can and this my friend really wakes them up . We like to run our engines 15,800 rpm and there reliable at that , have seen 16,500 on the tell tale but to much time there I question reliability. We've had great results and been approached by a lot of people for engines. Ps I also port and match the crankcase as this is also a major part of your transfers . Cheers.
@@adrianjackway5138 thanks Adrian, I will look into the finer finishing areas in a later video. Cheers again, Dave.
I noticed that there is space for 2 extra transfers ports between boost port and 2nd transfers.
You can mill a slot into the liner.
I also think the suggestions of single ring piston are viable.
I've noticed that blata mini moto 50cc pistons use ver very thin ring , single ring piston, possibly 0.6mm.
I've only got 40cc pistons or id post you one to try😁
Hi Peter, cheers for the suggestion 🙂
I'll have to have a look to see if it's possible... As I remember it does get quite tight there, where the cylinder bore gets close to the cylinder stud.
Single ring is definitely something I want to do but I need to change the conrod first (extra length and bigger small end)
Thanks for the offer too.
Cheers
Dave
@@AutoBeta2T why not make a different liner?
The intake has essentially 3 ports after reed valve- make a liner with either one or two inlet ports.
I believe a single port flows around 20% more than a divided port with same cross sectional area.
Regarding cylinder studs, cut the extra ports deep enough to reach stud space, then sleeve the stud space, to avoid air leaks etc.
You know that you are as deep as you can go then..... Very much like making love to a beautiful woman! Go as deep as you can until something breaks!........then ride it at full speed.....
A word of advice, .... do NOT use wood working "carbide bits " for porting, buy the correct metal cutting bits, .... much better control and finish .
Cheers for pointing that out Mike - I hadn't realised. Do you have a link or a name of the type of burr I should be using?
Nice!
I own a 1987 MBK CF (which mean Compétition Française) Group 2 competition moped with a 50cc cylinder and almost 13 horsepower. Top speed exceeds 145 Kmh (90 Mph). With a 93cc cylinder, it will be very easy for you to exceed 100 Mph.
To work on the transfers, I use a sheet of carbon paper, which I scan to optimize the shape with vector graphics software. Then I print the modifications with a laser printer and transfer the toner with a soldering iron into the cylinder, keeping it clean and free of grease. Finally, I mill it with a dentist's angle grinder... just like everyone else.
Hi again Siem, does you MBK CF have a fairing?
Also what do you mean by carbon paper?
@@AutoBeta2T On my CF, I have the original '87 fairing and that of the 1991 model. The 1987 front fairing is very fragile at the spider supports. The seat is a disaster, because it was a piece of plywood with resin. The wood isn't very well suited to all the vibrations, so I find it hard to understand MBK's choice.
Sheets of carbon paper are used to reproduce a trace on a sheet by transfer. In the days of typewriters, it was widely used. All I have to do is tape a piece of it into the perfectly degreased cylinder, and with a point (a fine nylon spudger for dismantling electronic things) I mark the transfers. Then I scan the sheet to make perfect tracings in Illustrator, Rhino (just perfect) or Inkscape. A laser printer printout of the modified tracings. I fix the laser print against the cylinder surface and iron the reverse side with a soldering iron set at 180-200°. Finally, the print toner is transferred to the chamber. I've been using this technique for over 20 years. It may seem complex, but it deserves attention.
Cheers Siem - I think I follow now. I remember copy paper when I was a kid. So the laser is used to create a laser template for the port windows which it then printed with the soldering iron activating the toner.
nice job on ex port.what comp ratoio are you running ? as you know this takes away some.
Hi Skyhawk, from memory it was 13:1 geometric, I can't remember what the corrected ratio was but as you say it will be lower now I've raised the exhaust.
I'll do an engine current spec video I think. I've lost track a bit myself and also I had the timing measurement wrong too so a reset and review of where I'm at should help everyone 😁
Привет! При увеличении периода выхлопа падает фактическая степень сжатия. Отчасти поэтому и наблюдается потеря производительности на низких RPM. Кроме того стоит уделить внимание и размеру карбюратора, однако это негативно влияет на диапазон крутящего момента. В таких случаях я использовал на своем 2т CV-carb. Так же хорошие результаты показывает boost bottle, если его удачно подобрать. Тоже имею собственный динамометрический стенд. Удачи и добра! Привет из Беларуси!
Привет, спасибо и спасибо за просмотр. Я подсчитал, что перешел от скорректированной компрессии 7,4:1 к скорректированной компрессии 7:1, увеличив выхлоп. Я заказал несколько голов на eBay, чтобы обработать их и провести еще несколько испытаний с более высокой степенью сжатия.
У меня есть еще один карбюратор, который стоит попробовать, диаметром 30 мм.
Какой размер бустера вы используете? Насколько, по вашему мнению, это дает увеличение в нижнем и среднем диапазоне?
Ваше здоровье :)
@@AutoBeta2T я пробовал разные варианты бустера. На самом деле подбор оптимальных размеров - трудоемкий процесс. Свою эффективность показывали бустеры как двухкратного, так и четырехкратного объёма двигателя. Однако более важный параметр - сечение трубки относительно сечения карбюратора. Чем больше сечение трубки относительно сечения карбюратора, тем сильнее влияние резонатора при полном открытии акселератора. Я использовал сечение трубки вплоть до 40% от сечения карбюратора. После этого при помощи формул по расчету резонатора Гельмгольца получал примерные размеры бустера. Прибавка производительности в моем случае достигала 5% при полном открытии дросселя. Очевидно, что чем меньше открыт дроссель, тем эффективнее работает бустер. Поэтому в естественных условиях ощущения от бустера заметно ярче, нежели на стенде. А настроить бустер легко можно на необходимую частоту вращения коленчатого вала путем изменения длины трубки. Особенно хорошо в этом случае помогает динамометрический стенд)
Так же, присмотрись к системе ATAC от Honda. Это достаточно легко реализовать в условиях мастерской. И это действительно работает. Я это делал пару лет назад и был в восторге. Однако ещё предстоит это проверить на диностенде, чтобы конкретизировать результаты.
Надеюсь переводчик преодолел все языковые барьеры)
Удачи!
Гениально, спасибо вам за всю эту информацию. Я думаю, что для того, чтобы получить мощность, необходимую для достижения скорости 100 миль в час с имеющимися у меня передаточными числами коробки передач, мне нужно будет улучшить кривую мощности внизу, чтобы иметь возможность включить 6-ю передачу. В этом была проблема первоначального задания - попытаться перейти на 6-ю передачу, не выпав из диапазона мощности. Может (будет) потребоваться либо бутыль наддува, либо система ATAC для повышения мощности среднего диапазона. Спасибо за информацию еще раз. С этой точки зрения похоже, что Google Translate очень хорошо переводит, поскольку все, что вы написали, я понял. Ваше здоровье :)
@@AutoBeta2T достижение 100 миль в час - весьма рискованное занятие. Достижения необходимой мощности здесь недостаточно, важно не вывести из строя двигатель по любой из множества причин. И воздушное охлаждение только усложняет задачу. Стоило бы подумать либо о системе Ram Air от Suzuki, либо о жидкостном охлаждении. Ну и конечно же было бы хорошо узнавать о максимально возможной скорости в реальных условиях через программное обеспечение диностенда. Не знаю поддерживает ли данную функцию Sport Dyno, однако Symple Dyno может рассказать о реальных способностях испытуемого. Конечно же для этого необходимо будет указать точные параметры мотоцикла. Однако это все равно хороший способ избавить себя от множества неудачных заездов на дороге.
Жму руку! Удачи!
Se alzi la fase, automaticamente devi alzare il rapporto di compressione.
Per un risultato ottimale.
Buon lavoro..👍🙋♂️
capito grazie
While it's quite nice to see u go through these testing steps might I suggest tightening up the testing parameters a touch . Taking care of the little things like welding the leaks in the exhaust, choosing a way to measure port timing that is repeatable and as troublesome as it may be, building a pipe that is correctly sized for your modifications. As a former drafter designer our attempt was always to remove any ancillary issues so that the test readings would should only the effect of the modification being made. I do sympathize with u take my word for it but it really is the only way to get the specific info your looking for. Anywho good job my friend and wishing u success!
Hi Matt, I do try to be as consistent as possible... I'm reasonably happy with the measurements of the ports now. The main leak from the exhaust is from the adjustable section in the dwell which I can't weld at the min as it wouldn't be adjustable anymore. Usually this joint does seal a bit better but it's not the best on this pipe. I'd like to do some more testing with this pipe so don't want to weld it up. The header leaked a bit too after I cut it down... This could be fixed.
Also, I do have another pipe to test that was designed around the higher higher exhaust timings. As with these things, time is the killer.
Look at Patrick Bächler´s channel. He too made an 100km/h-50cc-engine (62,5mph), with great coverage by the sole 2 gears of the original engine (no power-gap)... Even in his channels´s thumbnail, you notice, that his Sachs-cylinders have 6 boost-ports, and up to 11 ports altogether (always made out of original Sachs-cylinders by grinding new ports).
He also tried variable length exhausts (long for high and short for low RPM, stepless/smooth graduation), thus greatly stretching the peak-power-plateau of an engine (not part of the 100km/h-engine-challenge, tho). Ask if you need more details, since everything is in swiss-german accent, that even Germans hardly understand... Depending on what you search for, I can suggest specific videos, with some timestamps.
Hi Klaus, I've subbed to him and had a quick scan.
If you have specific videos with a timestamp theatre would be great.
I seem to be in a constant battle with time!
The top of the new cylinder i mean on the work bench with this your spoiling ports have also a longer period of opening duration and another benefit your carter volume is bigger take more air and cooling the crankshaft better than your tuned resonant exhaust pipe will take care providing power
A good way to find out how far to raise the exhaustport is by taking it off the edge of the piston first (just only from the edge exposed by the exhaust port), then start porting the exhaust port. By the time you went too far, you put back in an unmodified piston. Now you only wasted a piston, not a whole cylinder
Hi Fred, that would have been the plan and I have done it like you describe before; However, with the dykes "L" piston ring there is not a lot of distance from the top of the ring to the crown of the piston, also at the crown the diameter of the piston is around 2mm less than the rest of the piston so the exhaust timing is controlled by the ring.
If I had a more conventional piston I would have pushed a little further up to maybe 206 degrees filing the piston - just to see.
@AutoBeta2T hah, gotcha. That makes sense. In the past, I also have done, taking 2 mm off the top of the cylinder and adding it on the bottom with a spacer (1.5 mm aluminum and 0.5mm gasket extra) This brings everything (like transfer ports) up as well. 2 mm is acceptable, I think, without lowering (porting) the transfer ports. I can't remember what the numbers were for port timing, though. Good luck and have fun tuning (kinda jealous, I would like to do stuff like that again, but I live in Canada now. Not many 50cc shifters around)
Cheers Fred - yeah it's great fun (when it works) ☺️
Maybe a 50cc may come up?
❤❤❤❤❤
Another great video. look forward to seeing further gains with pipe, ignition,jetting etc. Like someone mentioned, what did EngMod2T say vs dyno? Next video with flow testing should be a good one too!
Hi Andrew, yes hopefully a little more to come yet... I've not rerun the sim yet. As I re-measured it looks like I was out a bit on the timing for the exhaust. This means maybe the same for the transfers?
Flow testing will be interesting as I've not done it before 🤞
@@AutoBeta2T This means maybe the same for the transfers? I would run the numbers in Engmod. I have a flow bench but only ever used it doing 4 stroke heads, throttle bodies/carbs/airboxs/ etc. Seen VHM did 1 video with their 12 degree piston but other than that haven't seen 2 many positive comments using it on 2T but nothing ventured nothing gained. The more info you have to analysis the clearer the picture becomes in my opinion.
Hi Andrew, any information is good I think. Even if it doesn't work at least you know :)
What about putting a radius onthe inlet port especially the center column divider bringing it into point leaving about 3 mm across surface, just a mm around the top and side that should increase the lower band as well. I thought the piston seemed a bit on the loose side is quite a gap can you get an oversized piston?
Jedi - noted, I'll have a look at the inlet inlet.
I'll double check the piston to cylinder clearance too.
Not the dykes piston crown is a few mm smaller than the rest of the piston.
When the outlet port is raised, the compression should be increased
Hi Wesulius, are you talking about the exhaust port being raised?
The compression stroke only begins when the ex port closes. When you raise the port you lower the compression. The solution is to reduce the combustion chamber volume.
I do the same experiment also. Raised the exhaust and wide it beyond the infinity you will make the scrap 😅... Just not to much 2/3mm for widening and raised is enough based on my experience 😊😊😊
Cheers Raymond - I would like to widen at some point but I need a spare barrel in case it all goes horribly wrong! 😁
@@AutoBeta2T sometime it depends on your head squish... After you get the best port raised and wide try reduce your head volume or increase compression 😅 i think it will increase little bit ..
(Im just suggest!!!)!✌️✌️✌️✌️😁😁😁😁😝)
Leave the exhaust duct small to keep the velocity high during the blowdown face
That's what I am thinking but what if it's too small now?
A coworker, and his father race 300 ft sand drags, mostly single cylinder 2 strokes, they build custom strokers, their own pipes, both welded cones and hydroformed, it really is art and science and magic.
Yep - it certainly is a bit of a black art. How do they find the hydroformed pipes perform compared to the cone pipes?
@@AutoBeta2T Dad likes the cones, because they showcase his TIG skills, his son says he thinks the hydroformed ones seem less "peaky" , but better through the middle, it's funny you ask, because they enjoy arguing about it as much as racing. Dad does all the designing / math, etc, the dude is a genius.....
@jamesgeorge4874 interesting,
It's one of those tests I've always wanted to do. It's really hard to keep the hydroformed pipes dimensionality correct. Maybe on to test in the new year 😊
You have to mill the head and reshape the combustion chamber to gain back your compression lost when raising the exhaust Port you need to have 210 + PSI and and then be careful with your fuel octane and ignition
Hi Jay, yes, I have a couple of heads off eBay to machine to get the compression back to where it was.
Hi we put the exhaust to 75% of bore at top on my 50 and it was a big gain with 206 duration with 15.1 compression
Cool - good to hear.
Any issues with 75% bore?
No maybe it we’re ring a bit faster but we can run about half the drag year on one piston and ring @@AutoBeta2T
Sweet - sounds like it's worth me widening a little then.
Remember, if you change the pot timing you have to adjust the pipe configurations as well. Port timing work along with your reflux gasses. Goodluck😉🥂
Cheers - a new pipe is in the pipeline 😊
Are you adjusting the tuned length on the expansion chamber? Exhaust port timing is tied to pipe length.
I use prof. Blair’s book and software for two strokes, all ports need to be adjusted for their wave activity to coincide for optimal power. Blair and his team placed p/t sensors all over experimental engines and exhaust and intake systems to come up with their algorithms. They are very accurate. Almost all software design systems now are based on his algorithms.
Hi, I've not done anymore pipe length adjustments. I did in my previous video here: ua-cam.com/video/yZXhKxrykCc/v-deo.htmlsi=l7hyJ6rlcGhphFVp but not this time after increasing the exhaust time area (and as a consequence the timing duration). Yep I've read quite a bit of Blairs stuff and EngMot2T the sim I use is based on his work. I have quite a collection of his SAE papers. It really facinates me, I did a video on the pressure waves computed by engmod2t - this was Blairs main aim: to be able to compute the individual left and right waves as realworld instumentation can only measure the superposition wave.
Wave visual video: ua-cam.com/video/jaAE-Bq2lvo/v-deo.htmlsi=Imc1IOOP4zAb_EJ8
Cheers
Dave.
For 4 strokes it is customary to consider .050" lift at the valve to be considered "open" for timing purposes. It's an annoying problem especially when you use radius top as I do. I've never been happy with the way it's done. I think you need to consider Time/area/FLOW COEFFICIENT in the mix, not easy to do.
Is there that to allow time for the flow to start?
@@AutoBeta2T It's really to distinguish the cam ramp from the actual lift part of the cam. The cam first applies lift in order to load all the components and take up all the flexibility/compress ability in the train. So it becomes hard to tell where the ramp up ends and the lift begins.
@@AutoBeta2T The flow actually starts the instant the first molecule sees a pressure differential. It moves at ~50% greater than the local speed of sound and those behind it follow as soon as it moves. The question is when does it make a significant difference to matter?
Find that out and you will be the first, that I know of.
The port is opening as soon as you get light showing through the top of the port/piston ring. Some exhaust ports are angled down at the top of the port, this make it very difficult to get a caliper measurment on the port depth.
Hi Gillian, agreed. I could get different readings with the caliper depending on how far into the exhaust duct they went. However, once I figured that out I could get pretty consistent readings. The 203 duration was from the light showing the port just cracking open method which I'm going to use as my standard now. Cheers for the info buddy.
Hello. Coating the piston with an anti-friction layer will be an experiment with the aim of increasing?
Cheers, maybe one day. I need to find a better piston :)
Come to think of it you have the means to discover the contribution of the radius. Test a port with minimal/typical chamfer on top then apply only a radius on it and test again, then raise it to the radius height with a minimal chamfer and test and finally apply a radius and test final. That should give you a good data set to judge the relative importance of height vs radius on the ex port.
Yep, it would be interesting. I'm not too sure what I'll be able to achieve with flow testing as I've never done it before but I'm sure it'll be interesting 🤔
@@AutoBeta2T What are you planning to use, a flow bench? and what configuration?
That is actually a fairly simple shape so I could calculate a very good estimation of overall flow given it's dimensions.
The best use of it will be probing the port to see if and where free jets form or if the flow attaches to anything.
Hi Bill, just something I found on the internet. All will be revealed soon but it doesn't involve a flow bench.
@@AutoBeta2T Ok I'll be interested to see it.
Me too 😁
Sorry if you mentioned it, I'm kinda skipping through quick before bed. What's your base ignition timing? I'm betting you can pick some of that lost low end by advancing the timing 15-20 degrees. Just a thought!
Hi Halverson, the curve I have programmed in is the BDK curve seen here: bdkraceeng.co.uk/Bike5.html
But I have moved all of the timings 2000 rpm to the right as the pipe is shorter.
In the next vid I do a bit of ign mapping to see if I can get a bit more power.
Excellent job man, I'd a 93cc (was bored out within an inch of it's life) when I was 16 and thought it was fast. If I only knew about porting and tuning back then. I'm building another AR93 and I'll for sure be using these videos for referance and inspiration.
Thanks Simon. I'm the same too, at 16 mine was quick I thought... However!
Yep, I was really surprised how much difference in power was gained from each 0.5mm increase in the exh port height. I've been told many times - it's all about ports and pipes!
WPC Treat all the internals, sprockets, wheel bearings, and chain. The friction reduction will help. Hopefully you have a facility in your country to do it. Thermal barrier coat the expansion chamber ( or make a new one ).
Hi Hoost, whar is WPC?
@AutoBeta2T you can look up the WPC treatment here and online. It's a micropeening treatment that destresses, hardens and reduces friction. Increases the strength of the component. Given that this style of two stroke needs all the help it can get, especially when it comes to controlling heat, this will help. That and a really good synthetic two stroke oil.
@hoost3056 cool, sounds good.
I'm running Motul 800 at the min. We used to race air-cooled 2 strokes and went from 747 to Motul and found it better.
You need to measure the exhaust timing with a dial gauge/protractor on the crank. From the degree the port opens to the degree the port closes. That's your duration.
Hi, yes I've seen that method but I like the direct measurement of the piston position. I find it's all a bit subjective 😁
I'll maybe give it a go and see what the comparison is like.
Is it worth checking squish band clearance? as you maybe able to reduce it but watch out for detonation though , great work on the ports though
Hi buddy - In the last vid I found the squish to be 0.45mm so possibly it needs to be greater.
Cheers to - pleased you like.
@@AutoBeta2T No probs I should have watched all videos ,anyway good luck hope you get your 20 +hp . Just remember in my 2 stroke days wide squish you lost power to tight detonation wrecked head and piston . Two stroke tuning is such an art , you can't chuck a cam in like on a 4 stroke
Thank you - hopefully I'll get the power before summer this year.
Have you done anything to regain the C.R. lost through reducing the swept volume?
Hi Ian, not yet, but I have just had two more standard heads arrive that I machine to test the current exhaust timing with the previous corrected compression ratio.
just wondering have ya tried a boost bottle from a rd 125 lc
Hi, I haven't but it is on my list of things to try.
Can you fit skinny tyres like the drag racing bikes in Thailand?
They are 150cc.
You could try throttle body fuel injection?
Also you could run a narrower powerband with a close ratio box.
If you raise primary drive gearing and fit bigger rear sprocket it will bring gears closer together, then set it so that 1st is where 2nd is now.....
Cheers Peter, The standard tyre is quite narrow. It is an option to try and get something a little narrower, or maybe a front of the rear too? I also need the correct speed rating which makes things a little more difficult...
I'd love to get a close ration gearbox, in fact I have one from a KX65 but It won't fit. I need to do a bit of research to see if there is anything that may fit.
@@AutoBeta2T as I said, you can make the gears close ratio by increasing rear sprocket size, AND raise primary gear ratio.
You can do a speed Vs rpm graph and see how this effects relative ratios.
The only downside is that 1st gear would be quite tall.
I was once intrigued by a BSA bantam 3 speed close ratio, " bog, blaap blaap blaaaaaaap" and that's it!
Also I notice that the intake port isn't ideal, 3 ports essentially - can you remove the 2 bridges so that it becomes one big port, just leave the upper parts to support the ring?
Or make a different liner?
You could always cheat and fit a kx cylinder, but then it wouldn't feel like an ar50 anymore.
I know you can buy 70 kits with 29bhp out of the box (mxs70) supposedly but they are crank case induction.
Your series of videos is probably the most interesting of all the tuning videos......2strokestuffing is the other series I like- in depth tuning discussion and the port height Dyno stuff is excellent.
If only it was piston port induction, that's what interests me most..... don't know why?!
@@AutoBeta2T btw did you check out the racing in Thailand?
maybe a little wider @ the blowdown aera and add a radius on the top contour of the port, good for ring life and duct flow. Also the transfers look small for a 93cc?
Hi Mog, yes, I have a little to play with on the width and - agreed about the transfers... I think I I measured them incorrectly and epoxied the roofs to lower the timing when I should not have. I'm going to have a remeasure of the engine and then go from there. I'll do a vid on it as a record and a chance for people to comment on the current spec. Cheers for watching and for the info. Dave.
@@AutoBeta2T great channel tho! long time ago i did moped racing in the netherlands. The rules where aircooled 50cc 4 speed with max. 16mm dia. carb or 12mm for 6 speed. We then had 10whp with a 4 speed tomos piston intake engine . But the top 3 had 14+ whp or so. What i can remember was the golden rule of 28/30 degree blowdown with 130 transfers, exhaust as wide as possible (without transfer interferance) , a good tuned pipe and you'll be good. Looking to your setup 25/30ish whp should be possible with unlimited carburetor dia.
Cheers Mog, I used to race 50cc too in the UK. But we were Am6 and Derbi 50's lots of fun racing!
I think if the exhaust is around 200degrees and the powerband hits at about 8,5-9,5k theres alot of room for a harder hitting pipe thats a bit shorter so it will peak closer to 11k? I once checked my DT125R exhaust port and it had more duration than a 1989~ YZ125 exhaust port 🤯
Sure the rideability goes down alot from not having a powervalve but from the dyno I'd say it doesnt have much kick to it and the power curve is pretty wide.
Cheers, I need to look at the exhaust again. I'm up for making more pipes... The current one is just a base pipe. Hopefully we will learn more from testing different pipe designs 😃