One thing I remember about chamber sizing and power, with valve jobs and combustion volumes being equal, the engine with the smaller cylinder head chamber volume would make power more efficiently than an engine with a large cylinder head chamber. Something to do with reducing the amount of dome on the piston, while having the same compression ratio, would help increase combustion speed, and would also reduce the ignition timing advance needed to make peak power. It apparently also reduces the octane requirements, between having a faster combustion speed, and having less surface area in the combustion chamber, which both helps reduces the chances for knock. If possible, it's one of the things I would like to see tested on the test mule if that theory by itself holds true, or if there's factors missing on that theory.
As I think about it, the stream of exhaust pulses moving down your headers present a net negative signal to the intake during overlap. But the chamber tilts things. So we can think along the lines of vacuum. That means... the combustion chamber behaves kind of like an accumulator: the smaller the chamber, the faster it can equalize, therefore intake charge can begin moving sooner. Thats not exactly what happens of course, :but objects in motion tend to stay in motion, and so it is with the bulk of exhaust gases and their net effect on intake charge. Overlap time is a very small window and it gets smaller as revs go up. If I didn't screw up the math, a 58 degree overlap at 6k rpm's is 3.2 milliseconds [as cam is half speed of crank]. Do valve jobs matter in such circumstances? Oh yeah. Any pros want to correct the math, thanks in advance.
@@pacman3908 its more efficient combustion. Look at the Trick Flow Ford head making with a specific cam , rockers and springs making 423hp on a 302 according to Trick Flow . Intake airflow is ( by head so I could be off a little) 265 cfm. I have made several 289 cast iron heads ( 1963 to 1966 ) only having intake air flow of 208 cfm as restricted by valve size as per FIA regulations , and designed for endurance ( hours of Spa , Classic Le Mans ) therefore also limited to 0.530 lift as ball rocker will burn if more lift used , but making 438 hp on a real 289 ci engine with dual plane Edelbrock. Main difference is combustion chamber design. Actually....dome height/ size. Thats what makes the power. Whereas for first years working on those 289 aiming for highest airflow with still stable head design as its used for endurance ...I now balance between airflow and dome size to extract most hp. And for some its hard to believe as they want to see high airflow numbers regardless of how chamber shape gets achieving the highest airflow.
So to make the same compression with both heads the 70cc head will need an 15cc dome on the piston. So in reality when the engine is assembled which cylinder will have better flow, the one with the dome or the one with a flat top piston?
Eric, what does it do on a running engine. The loss of flow vs the compression gain? Also how much more, I imagine $500 to $800, is the cost of angle milling the head from AFR? Thank you and I hope this question gets to you.
Having angle milled fuelies in the distant past 0-80 theynworked well and I had 12-1 with flat tops. Would I do it agauin?? No. A decking the block achieves more for less. B if nesecary use a small dome piston. Big dome pistons are a bigger hindrance to power. Less compression is really preferable
Great video Eric! I may have missed it, but is there a difference in flow between the stock heads without milling (comparing a 76 cc chamber to 66 cc chamber?) Thanks!
That's a very substantial flow difference, enough to make a power difference. I flat milled my AFR 220's .030 and ran into that top cut pretty good, about like the heads you have there. Plus, the chamber is shrouded more on the outboard side of the head when they're milled like that, so the chamber needs cut out to the bore size to deshroud it again. How do I fix the valve seats where they're back up to par?
Do you have any advice for switching to an aluminum head? I have a warmed over '69 412 block 427 with 840 heads. Compression is around 11:1 and it's around 500hp. 840 heads are a closed chamber 107cc Rec port. I need to cut some weight without losing any Tq/Hp in my Nova (3650lbs with me in the car)
Greatly appreciate this video sir, I’ve been trying to learn about this a lot as I’ve recently had a set of old rhs pro action factory 50cc heads redone for my small black build and I haven’t been able to find much good info on chamber size
Does airflow velocity change when valves are opening ,as in piston starting to move when pulling air in past the valve (piston speed) compared to flowing a head on a bench with air at a constant speed or am I overthinking it
One thing I remember about chamber sizing and power, with valve jobs and combustion volumes being equal, the engine with the smaller cylinder head chamber volume would make power more efficiently than an engine with a large cylinder head chamber. Something to do with reducing the amount of dome on the piston, while having the same compression ratio, would help increase combustion speed, and would also reduce the ignition timing advance needed to make peak power. It apparently also reduces the octane requirements, between having a faster combustion speed, and having less surface area in the combustion chamber, which both helps reduces the chances for knock.
If possible, it's one of the things I would like to see tested on the test mule if that theory by itself holds true, or if there's factors missing on that theory.
It's called more quench
As I think about it, the stream of exhaust pulses moving down your headers present a net negative signal to the intake during overlap. But the chamber tilts things. So we can think along the lines of vacuum. That means... the combustion chamber behaves kind of like an accumulator: the smaller the chamber, the faster it can equalize, therefore intake charge can begin moving sooner. Thats not exactly what happens of course, :but objects in motion tend to stay in motion, and so it is with the bulk of exhaust gases and their net effect on intake charge. Overlap time is a very small window and it gets smaller as revs go up. If I didn't screw up the math, a 58 degree overlap at 6k rpm's is 3.2 milliseconds [as cam is half speed of crank]. Do valve jobs matter in such circumstances? Oh yeah. Any pros want to correct the math, thanks in advance.
@@pacman3908 its more efficient combustion. Look at the Trick Flow Ford head making with a specific cam , rockers and springs making 423hp on a 302 according to Trick Flow . Intake airflow is ( by head so I could be off a little) 265 cfm.
I have made several 289 cast iron heads ( 1963 to 1966 ) only having intake air flow of 208 cfm as restricted by valve size as per FIA regulations , and designed for endurance ( hours of Spa , Classic Le Mans ) therefore also limited to 0.530 lift as ball rocker will burn if more lift used , but making 438 hp on a real 289 ci engine with dual plane Edelbrock.
Main difference is combustion chamber design. Actually....dome height/ size. Thats what makes the power.
Whereas for first years working on those 289 aiming for highest airflow with still stable head design as its used for endurance ...I now balance between airflow and dome size to extract most hp.
And for some its hard to believe as they want to see high airflow numbers regardless of how chamber shape gets achieving the highest airflow.
Be very interesting to see how the dyno #'s would look between those two heads as CFM is not everything. But great info!
I respect you don't want any drama, so deleted comment , Thanks for the content 👌
Very good information
Thank you for the video!!
Great video,thanks Eric
So what is the benifit of angle finish ? thanks for sharing, all the best to you and your loved ones
So to make the same compression with both heads the 70cc head will need an 15cc dome on the piston. So in reality when the engine is assembled which cylinder will have better flow, the one with the dome or the one with a flat top piston?
I bet the 1 with the flat top
There is a great calculator on Wallace Racing Calculator
Great video
Eric, what does it do on a running engine. The loss of flow vs the compression gain?
Also how much more, I imagine $500 to $800, is the cost of angle milling the head from AFR?
Thank you and I hope this question gets to you.
Having angle milled fuelies in the distant past 0-80 theynworked well and I had 12-1 with flat tops. Would I do it agauin?? No. A decking the block achieves more for less. B if nesecary use a small dome piston.
Big dome pistons are a bigger hindrance to power. Less compression is really preferable
Wouldn't doing a radius skim cut on that valve seat to help flow on the angle milled heads? I'd think bumping it on the Serdi would help 🤷
Great info Eric, it is amazing the order of operation to make the head come out correctly.
Great video Eric! I may have missed it, but is there a difference in flow between the stock heads without milling (comparing a 76 cc chamber to 66 cc chamber?) Thanks!
That's a very substantial flow difference, enough to make a power difference. I flat milled my AFR 220's .030 and ran into that top cut pretty good, about like the heads you have there.
Plus, the chamber is shrouded more on the outboard side of the head when they're milled like that, so the chamber needs cut out to the bore size to deshroud it again.
How do I fix the valve seats where they're back up to par?
Lets say a head will be angle milled to get at a 21 degree setup. How to correct dowel pin holes?
Great question but I haven’t had a problem with it so I don’t know.
Get holes perpendicular to the deck, not parallel. I’m picking nits but I still love the content.
Wouldnt a larger chamber require less material removal to drop the cc volume compared to a smaller one?
Wouldn't it be easier to get a dome piston
Do you have any advice for switching to an aluminum head? I have a warmed over '69 412 block 427 with 840 heads. Compression is around 11:1 and it's around 500hp. 840 heads are a closed chamber 107cc Rec port. I need to cut some weight without losing any Tq/Hp in my Nova (3650lbs with me in the car)
Greatly appreciate this video sir, I’ve been trying to learn about this a lot as I’ve recently had a set of old rhs pro action factory 50cc heads redone for my small black build and I haven’t been able to find much good info on chamber size
Will a difference from 63cc to 70cc make much difference in efficiency all else being equal?
Does airflow velocity change when valves are opening ,as in piston starting to move when pulling air in past the valve (piston speed) compared to flowing a head on a bench with air at a constant speed or am I overthinking it
Changes in impingement of flow to top of the bore?
I'm shocked that AFR will mill into the intake seat. I would be weary.
No worries. Especially since they carry a lifetime warranty
Can a head with steam holes be used on a block that don’t have them?
Yes
Why do it then??.
Compression ratio increase.
Gotcha
I've been watching your video's and Steve Morris's. One of y'all need to change your voice, y'all sound too much alike. It's confusing me. 😄🤪
🤣🤣🤣
Great video