Unlocking the secrets of 2 stroke porting, part 2 - How to trace and measure ports.
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- Опубліковано 18 кві 2019
- This is the second of a series of videos on the topic of 2 stroke engine ports that you need to know if you are intending to modify your engine.
The first 3 videos will cover simple mapping of the exhaust port and transferring that in to 2T Exhaust Calc software for the purpose of Expansion chamber exhaust calculations.
Freeware 2 Stroke Expansion Chamber Exhaust calculator program
Download at birdcagesoft.com
(Page link on sidebar at site)
#2Stroke #ExpansionChamber #Porting - Авто та транспорт
NOTE if anyone is wondering why this video does not include all the other ports except exhaust and does not slice the port up into segments for the purpose of time area analysis then before smashing the dislike button in protest try watching the first video of the series for the explanation about why we are only doing the exhaust in this video and only doing the total area of it.
InstaBlaster...
Super great information to know! I really enjoy watching Your videos. Porting is so important to know and th get right the first time! It's easy to take off but is impossible to put back on! Keep up the great work my friend. Looking to the next video!👍
Wow I’m blown away with your content. Awesome stuff! Thank you so much for sharing and teaching. I’m using your software to build a pipe for one of my chainsaws. I built a dyno to test saws for power and torque. I’ll let you know what kind of results I get. I see others having huge success with tuned pipes on saws. Can’t thank you enough for all your help. Happy tuning from Minnesota, USA
Glad you like the content.
Thanks for the comment.
Thank you Sir for this great video. This gives me a better understanding as I am building the expansion chambers for my motorcycle. Thanks once again and much appreciated!
Thank you for the comment
very sound explanation, thanks
Great demo of using stuff you have laying around to get measurements, instead of splashing out on a set of radius gauges etc for a job you might only do once or twice 👍
Yeah I like to use what Ive got or make my own tools if I can, save a few bucks too.
Can't wait for the next video
Me Too, lol.
so great , well explained and very informative. planning on just tune my scooter a bit. i can get away with just buying things and bolt on, part combinations that work for other people. but im kind of interested in the science/mechanics behind it all. but ive noticed that its hard to come by deep knowledge about the subject, and im just too curoius about it. thx for all good and great explained videos, and ive just realised i shoud have gotten a engineer or mechanics education instead of arts :)
Knowing a bit about how the parts you are buying to modify it work can help making your selections and gives you some idea on what gains to expect from them.
very cool content man. good information.
Glad you found it helpful.
Very Good information.
Thanks for taking the time to do these video,s.
I know sometimes it seems the information you share is it worthwhile ?
But from the look of the early comments it seems it is very well received.
I guess just keep doing video,s if it makes you happy, and hopefully with more time more people will watch.
Thanks again.
Peter.
Thank's for the comments
I do enjoy doing the vids.
@@AuMechanic
How far off are you with Part 3 ?
Part 3 will be up tomorrow.
@@AuMechanic
OK Thanks for letting me know.
See you then.
Peter.
THANK YOU SO MUCH!
Finally...something that makes SENCE.
Added a video to my channel using your exhaust port Calculator. Would appreciate your comments if I did it correctly because we have two exhaust port window that each have 4 different radii.
Cool
Thanks
a general question:
in case that i have a cylinder which has a piston ported intake.can i determine my max. carb size after measuring and calculating the intake port area? (as in calculating the crab area and choosing a diameter which gives me a smaller area closest to the port area.)
or is it ok/common to go bigger?
Good question and in short yes
Starting figures (as given by Blair) would be the carburetor flow area should be between 85% to 95% of Intake port area of a piston port engine.
This is based on the specific time area of the intake port since it is not area alone that determines how much air flows through it but also time it is open for, re timing and RPM.
Ill be doing more on ports other than the exhaust fairly soon.
You can use aerosol shoe spray. Its similar to graphite lube, but it sticks without bleeding. Cheers!
Good tip.
There are a few methods to do it which are all ok so long as it gives and accurate cope of the port.
Makes sense so far. Do transfer port sizes and locations matter?
Yes they do but we are just doing the exhaust to begin with for the purpose of expansion chamber calculations.
I will be covering the other ports later.
Sounds great. How do people make the rolled sections of head pipe with cone software one dims are all calculated?
The software has a function to plot the diffuser and baffle cones on to sheet metal
I did a video earlier on that here ua-cam.com/video/BqYEagl6AHQ/v-deo.html
To do the bent header section is a bit more involved and Ive put a ref to another software to plot a curve taper pipe called "Cone Layout" Google it.
Sir, I need such a help. I want to ask about the port of such a cylinder, how can we increase the speed from its port. Please help me. Please tell me.
I install chainsaw and scooter cylinders on motorized bicycles. In the program it asks for stroke and I use a spacer. The crank is 40mm but it has a spacer to use small stroke cylinders cylinders. My question is do I go by the stroke on the crank or the piston movement stroke in the software?
A spacer under the barrel wont cause any difference between the stroke of crank.
It only modifies the position at which that piston starts and stops in its travel form BDC to TDC
Can I please ask for the sake of your fantastic expansion chamber design software .
My Yamaha ypvs barrel has an exhaust port that angles up towards the piston . What measurement do I submit for the length of the port as it changes depending at what point you measure it . Do I just take it from the centre point ? Thanks in advance .
Yes use a centre line measurement for the purpose of pipe equations.
Thanks again
Would it be possible to use liquid volume to measure the port surface area? Like if you sealed off the port from the inside and filled it with water and measured the volume of water in a syringe.
"Area" is only 2 dimensions (height and width) and "Volume" is 3 dimensions (height, width and depth)
Knowing the volume you wont be able to extrapolate the width and height from it so there is no point in measuring volume.
@@AuMechanic I just watched more and have a better understanding now. Thank you for this excellent content. You make me feel I can do this with my intermediate experience.
Novice question- Obviously, this would be done AFTER port matching, correct? As far as measuring exhaust port open duration, this would need to be done with a rocket key installed if you are planning to install one, right?
@@phreaktor Yes you would do it after any port work.
Does any of this change with a power valve engine? Do I still measure the port opening in the bore and ignore the valve?
Sorry if this has already been covered
Yes measurements are taken at port window at the bore for maximum port window area.
G'day mate. I've been watching with great interest and I have an exhaust question for you. I'm probably going to couple a pair of Zenoah 29.5's together and run them in a large scale hydro. My question to you is, should I run 2 seperate exhaust pipes or make a 2 into 1. Which would give the best top end?
1 pipe per cylinder is best.
That said for a fixed installation at constant RPM a 2 into 1 might do.
I cant help much on the 2 into 1 design though.
I've got kind of a strange two-stroke theory question that I can't seem to find an answer to anywhere. Do any manufacturers or tuners use a dual intake? Like, a piston ported reed valve as well as case induction?
Suzuki had a combination of intake types back in the RM off road series that was a combination of piston porting with case induction reed that had a strong mid range power but not as strong in top end RPM range as standard reed.
@@AuMechanic were these single carburetor? I have seen a small power equipment engine with two carbs, but not a single carb, dual intake. That's what I hope to accomplish with a bike this summer
Single carb on the RM
Yes some chainsaws have dual throat carbs on them and a few bikes too, these are commonly 2 stage carbs where one carb throat opens at lower throttle, that provides better fuel mixture control at par throttle but on saws is likely for emissions compliance since the simpler walbro single carbs they usually have are pretty rudimentary.
2 things, my port exit or flange is round, so i assume its simple to work out that effective diameter. my exhaust port is lower than the piston at bdc, so i suppose i should draw the port as it actually is ie subtract the bit covered by the piston or just look at the hole that is open at bdc.
Yes
Ive done a previous video that covers some equations for calculating the area of parts of ports.
i cant find it. have you got a link or title please?
@@aljaxon69 See video called "How to Design a Two Stroke Expansion Chamber Performance Exhaust - Step 5"
Hi, if the exhaust port isn't straight, in this case it slopes down, how is it best to measure the port lenght? For example if I measure the horizontal distance from the face of the piston to the face of the exhaust flange where the gasket goes I get 44mm. If I measure down the slope at centre line at the top I get 50mm, at the bottom 55mm and if I measure down the slope at the side at half the vertical height of the port I get 60mm. Any help gratefully received.
You could just measure the length from piston to flange at the top and the bottom and average out the 2 measurements.
@@AuMechanic HI, thanks for the reply. Just to clarify: is that measured down the slope (ie 50 + 55 /2 = 52.5mm from above) or exactly perpendicular to the face of the piston (44mm)?
@@davidwatsham2750 Measure down the slope of the roof and floor and average out the tow measurements.
Chomping at the bit to see these porting videos! I have a similar kind of engine and the port durations are miles away from the suggested amounts by the likes of Bell etc. It is more of a chainsaw engine though, dunno if that makes any difference? All I've done is widen the exhaust port to 65% of the bore so far.
All that differs is the parameters used depending on the application.
Some applications use similar engines to chainsaws so a few modifications can be made to suit that use of them.
Just making the port wider can provide simple gains, where raising the port also changes to port timing so care needs to be taken doing that because you are changing more then just the port size but also the time it is open for and that impacts on other factors like blow down time for example.
@@AuMechanic my durations are EX: 147.5 Intake: 139 Tran: 105 BD: 22.5. The bd looks sensible but the transfer and ex look really low, looks like its tuned for low RPM? But the intake is relatively high though don't you think?
That's pretty normal for a chainsaw keeping in mind that they lean toward noise and exhaust emissions too so the exhaust timing is pretty conservative for that reason, and blow down being the diff between exhaust and transfer opening means that a low exhaust will have a low transfer timing to ensure a adequate blown down time.
So what that means in short is for the purpose of best power there is some gains to be had in increasing ex/tr timing.
@@AuMechanic That's great, cheers! It does mean raising them both significantly. Would there not be a disadvantage to raising them so much that the piston doesnt get a chance to travel down much before exhaust gases leave the cylinder?
It will reduce the trapped compression ratio which if it has an integral head and barrel is a bit limiting because you can't skim the head to bring it back up.
As for the exhaust gases so long as the blow down time is adequate then that should be fine keep in mind that the ports will be open for longer as well as being a little larger.
What software did you use to calculate sir ?
A free pipe calc software I wrote
You can find the download site link to it in the description section under the video.
Why this exhaust port have lip on port top?
Do you mean the small slot in the cylinder above the port ?
If so that is to reduce exhaust noise by slightly reducing the pressure differential between the exhaust port and the cylinder pressure to reduce the peak of the sonic compression wave created when the port opens.
I will be covering this in a later video on the reason for various port shapes.
Thank You @@AuMechanic
One question: sometimes high gas speed is good, but at the same time narrow means restriction.
Can you explain?
Good question but a but I bit much to cover for the comment section as it all depends on which port and which end of the ports to. it is an expansive topic
I will do some more on this in ensuing porting videos.
That is true to some degree but then any engine will eventually be run at WOT at some point.
For the transfer for example too slow an air speed near the cylinder end of the ports may results in poor scavenging, while too much may cause excess intake spilling out the exhaust.
And for reeds you want enough air speed to give a positive opening of the reeds while on the flip side keeping the pressure differential across the reeds as low as possible.
Other parts of the ports can be subject to turbulence as air speed rises that can limit bulk flow and for intakes increases in air speed can cause separation at bends where the air goes around corners fast but the fuel droplets want to go straight ahead into the port walls.
It very much depends on the port and where about in the port and the engine in question and other factors which will probably take up a few videos just on those aspects.
Why couldn’t you just have used the caliper to measure the exhaust hole
You can use one, but that will only give you height and width of the port and you need to measure the radius corners as well.
And to measure the inside of the port at the cylinder your calipers may not reach so you will need to use a bore gauge of some kind of inside calipers.
Cainsaw Zylinder?.
The one in the video is not, it is just a small cheap 2t engine I bought to use in the videos.
I do have a few chainsaws I do work but I don't get much time to use the parts to make videos as I am repairing them .
The magic is in your die grinder and your head.
Or the hand operating the die grinder.
While the head has some bearing on the power and Ill be covering more on that soon in squish bands, there is no real magic bullet with power in 2 strokes, you need to get quite a few things all working for you to get big gains, otherwise gains can vary greatly.
Ooh. My goodnes. Now i si it. Meby a Pocket Bike Zylinder. U Open the Port. The have a Bad. Motorblock. Put it togeter End End do the Piston Up End Down.
Sory fohr. My feal. I watch on the Internet oredy. Is Not the Motorblock. Meby the Zylinder is Not corekt. Bad Open the Port is ok.
It's easy to cut through the exhaust port to the outside world!
It's useful to carve the transfer ports wider towards back if cylinder, get more flow as they open because the transfer ports are fed by such narrow channels.
I raised exhaust significantly and had to seal the holes up!
But the restrictive transfers mean that you just lose torque as they can't flow enough for higher rpm?
Plus you lose compression with the head and cylinder being one piece.
I bought a big bore race cylinder.....same bore!!! Plus the ports were all low so at BDC you could see rings through ex port yet at tdc piston was at top in correct position!
Useless!
Yes it is common for many to start hogging out the exhaust port to begin with but that said modifying the exhaust can be more forgiving where the transfers can really end the party if not done right, so just doing the exhaust alone is not such a bad idea for those new to it so long as they make small changes to begin with and test the results. Also important to be neat and precise about the port window too.
Also we all know that good tuners are in fact witches and use magic to chest.
No matter what you put in a video some people will pick fault 🤯💩😁
I'm not averse to critique so long as its not combative and they can cite sound logic for it then its fine.