High compression heads

[Lexveen]

I am considering to change my Z head for a Prus head from Snyders or a Sherman style head from Lang’s. These look the same, but did anyone measure the volume of the chamber?

[Oldav8tor]

The question is "Why"? I doubt you'll see much difference. I saw dyno test results of a Z & Prus and they were similar.

[ModelTWoods]

I haven't looked at Lang's online catalog for a cylinder head and they haven't sent me a catalog since 2021 (I guess they haven't published a more recent one), but I was unaware that there was a third "sherman style" option. The only two heads that I knew were available were the "Z" and the "Prus", and from what I know, the Prus is a "sherman style". When the Tulsa MTFCA chapter tested and compared heads, the Prus wasn't on the market, but the Z, was. The volume of the stock Z was 12.4. A Z milled .050 decreased to 11.5. A Reeder head (no longer on market) was 12.2. A Prus should be less, plus the quality control is better and the combustion chamber is machined; not as cast.

[TWrenn]

Why not high compression pistons?

[speedytinc]

Why not high compression pistons?

He has a Z head now. Cant use high dome pistons with these heads.

[speedytinc]

I believe I have combustion chamber CC's for both heads. Can post later tonite.
The Z head varies quite a bit from casting variations.
Prus are consistent. A recent compression test on a Prus head showed 82#
You might want to do a compression test on your installed Z head for comparison.

[ModelTWoods]

Why not high compression pistons?

He has a Z head now. Cant use high dome pistons with these heads.

You are correct with "as cast" high compression pistons, but I know that if careful measurements were taken and accurate machining with a vertical mill were done, that parts of the dome on high compression pistons could be removed, leaving only part of the dome that wouldn't interfere with the high compression head. Yeah, it sounds like a lot of useless extra work, but I've read here on the Forum of guys doing just as time consuming work, just to see if it could be done. I plan to try it on an engine or two that I'm building.

[AndyClary]

I think the Langs head may well be a Prus head.


Andy

[ModelTWoods]

I think the Langs head may well be a Prus head.


Andy

I agree, Andy.

[John_Aldrich]

I believe I have combustion chamber CC's for both heads. Can post later tonite.
The Z head varies quite a bit from casting variations.
Prus are consistent. A recent compression test on a Prus head showed 82#
You might want to do a compression test on your installed Z head for comparison.

82# is great compression!

[kelly mt]

I'm running two Prus heads and the quality is top notch. I average 80 psi on both. These cars pull hills very well which is why I put them on. Here is a comparison of a Prus and a Sherman Spit Fire head. Prus is the new looking one.

[speedytinc]

Z head CC'D @ 223 (after machining combustion chambers to match)
Prus head CC'd @ 220. Out of the box with the same volume for each chamber.
Similar. Prus advantage of wider between 1 & 2 & 3 & 4 and no future corrosion issues.

[Gene_French]

Lex:
choose the Prus head ... i have had to machine EVERY Z head i have installed ( 7 total ) ... the Prus head has machined chambers of equal size and is treated to seal porosity and resist galvanic action ... Gene French

[TWrenn]

Why not high compression pistons?

He has a Z head now. Cant use high dome pistons with these heads.

Well what I meant was why not use HC pistons INSTEAD of HC head

[speedytinc]

Done motors that way. Dont have a compression reading with a high head, but, a milled low head can make 90-95# compression.
I dont recommend the extra milling on a low head.

[AndyClary]

My 14 runabout has high compression pistons and a low head. Runs great and looks correct.


Andy

[Kevin Pharis]

Well what I meant was why not use HC pistons INSTEAD of HC head

Each has their benefit and drawbacks, but mostly a matter of opinion. High dome pistons increase compression, but also add additional weight to the reciprocating mass of the engine (compared to stock profile aluminum). Some want the Ford iron head, some want the extra water capacity of the aluminum head, while some want the improved chamber design of either an iron or aluminum accessory head. We all have our reasons

[ModelTWoods]

Well what I meant was why not use HC pistons INSTEAD of HC head

Each has their benefit and drawbacks, but mostly a matter of opinion. High dome pistons increase compression, but also add additional weight to the reciprocating mass of the engine (compared to stock profile aluminum). Some want the Ford iron head, some want the extra water capacity of the aluminum head, while some want the improved chamber design of either an iron or aluminum accessory head. We all have our reasons

Good Points.

[TXGOAT2]

The Prus head looks like the pockets over the valves are deeper than the Sherman, which might give better breathing at higher RPM. The Sherman might make better torque at lower RPM. The head, carb, intake manifold, cam profile, and exhaust will all affect performance.
I believe that a Ricardo-type head like the Pruss or Sherman or the Z on an otherwise stock T engine will give the best bang for the buck.

[TXGOAT2]

I wish the Pruss head had the Ford logo on it....

[ModelTWoods]

I wish the Pruss head had the Ford logo on it....

Pat, Kevin said he left the Ford script off the heads to eliminate the hassle and expense of Ford licensing, and because by 26-27, Ford had omitted the script entirely from original heads.

[speedytinc]

Lex:
choose the Prus head ... i have had to machine EVERY Z head i have installed ( 7 total ) ... the Prus head has machined chambers of equal size and is treated to seal porosity and resist galvanic action ... Gene French

Exactly.

On both points + they are narrow between cylinders to be not head gasket friendly.

Z heads were ok(better than stock or recardo HP wise.) before the prus head if you were a machinist.

[AndyClary]

I wish the Pruss head had the Ford logo on it....

Pat, Kevin said he left the Ford script off the heads to eliminate the hassle and expense of Ford licensing, and because by 26-27, Ford had omitted the script entirely from original heads.

Understandable, but a low style head with script would be nice. I had a couple low reeder heads but they had corroded badly.

Andy