High Compression Head

J

jeepguy1948

Well-known member
I’m curious, do the “High Compression Cylinder Head’s) as sold by Snyders etc. have a different combustion chamber than stock or are they just shaved stock type heads? Put a different way; can you make a high compression head by shaving a stock head? FWIW, I already have one of Jim Brierly’s heads, I don’t actually plan to do this, I’m just curious.
 
The marketed "high compression " heads have a different shape combustion chamber. Due to the shape of the original Model A head, shaving the head will have little effect on the combustion ratio.
 
This slide shows the differences between the various combustion chambers.
 

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Fullraceflathead said:
The combustion chambers shape of the high compression heads is a much more efficient design than the original design.
Click to expand...

When dealing with very low numbers like a model A, just the increase in pressure has more effect than the chamber design.

The ideal chamber design seems to be ignored by the head designers so far.
 
Because no one has mentioned it yet, I'm beginning to doubt myself but don't the pistons in a Model A engine come above the top of the block? If so, shaving the head too much will result in them hitting the head. NASTY!
To put it bluntly, don't be tight. Buy a HC head that was designed to work at the higher compression ratio.
 
A shaved head will work just fine as long as you recut the piston clearance and check to make sure the valves will not hit. You have to take a lot off so you may get into the water jacket. I had a shaved head on my Model T which worked quite nicely. It was a "low head" to begin with so the compression ratio was fairly high. Quite a lot was taken off, over half an inch, so it was into the water jacket in places, but the head gasket sealed off those areas. I had to use shorter head bolts.
 
Pete had a valid comment when he said that the ideal design was being ignored. I agree with him. The racing flat heads for the Harley Davidson and Briggs and Stratton engines are more ideal. There may have been some custom heads with more ideal combustion chamber shape, but, in my opinion, none of the ones offered today are.

The incoming air makes too many sharp turns in a flat head engine, especially a Model A engine. It starts at the entry into the block where the air has to make a couple 90 degree turns before getting to the valve. Then it makes another sharp turn to go down into the cylinder as the piston retracts. The inlet port in the block should be angled upwards towards the valve with one port for each valve. Then the part of the combustion chamber that directs the air down into the cylinder should have a generous radius and plenty of area atop the cylinder to allow an easy path for the flow. The intake manifold is another restriction, but that is another subject.
 
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That’s interesting
The Yapp Lion and Rocket heads are very close to some Briggs Jr drag heads
Brierley has a close Harley Davidson design
Both of these work very well
There are others that require changing pistons but are marginally better


If you want more go OHV
J
 
The "crowfoot" Winfield head is a good one, Jim Brierly's head looks good also. Both of these are different from each other. Harley put a lot of effort into their design making it worthy of consideration, they also got some good results with it on the track.

OHV is best, but if you can make a Flathead run strong you have something to be proud of.
I like my Flatheads. :)
 
In my opinion, Jim Brierley is one of the truly great’s in the world of high performance banger motors. I feel fortunate to be able to acquire one of his cylinder heads, Synchro, it’s cool, I was just messing with you a bit. I always appreciate your input.
 
Flathead said:
The "crowfoot" Winfield head is a good one, Jim Brierly's head looks good also. Both of these are different from each other. Harley put a lot of effort into their design making it worthy of consideration, they also got some good results with it on the track.

OHV is best, but if you can make a Flathead run strong you have something to be proud of.
I like my Flatheads. :)
Click to expand...

I like FHs also but sometimes like to go a lot faster
It is all good old iron making ponies

J
 
jeepguy1948 said:
In my opinion, Jim Brierley is one of the truly great’s in the world of high performance banger motors. I feel fortunate to be able to acquire one of his cylinder heads, Synchro, it’s cool, I was just messing with you a bit. I always appreciate your input.
Click to expand...

THANKS jeepguy!
 
Keep in mind a Briggs & Stratton or Harley KR have distant similarity to a model A.
You can only expect their head designs to perform mediocre on a model A, which they do.
 
He who has the head on the engine with the biggest dyno sheet numbers, wins...

Probably still Ed Winfield.
 
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