High Compression Heads

[JBog]

Which is best? Also, is 5:1 or 8:1 more safe on a stock engine? General thoughts?

[JBog]

Sorry, I think I meant 6:1.

[greenacres36]

I have a Prus head on both my cars. They run great and the quality is outstanding. major power improvement. I don’t see where they would be any more hard on the engine and unless you run the devil out of it. I do believe the Prus Head prefers a little less timing advance.

Just my opinion. Opinions may vary.

[kelly mt]

I'm running two Prus heads. They run real good and the quality is outstanding. I have a lot of miles on them running in the mountains and work them hard. No lower end problems.

[JBog]

Do the vendors sell Prus heads?

[greenacres36]

They are the ones labeled 8-1. A little misleading as I’ve heard they are closer to 5.5-1 or so. Someone may correct me. Mine has a “P” near the water outlet.

[Joe Bell]

I have always liked the old iron high compression, they heat and cool at the same rate as the block so with less chance of head gasket failure. Of the old iron ones the Giant Power was one of the tops, that head combustion chamber went into the Z heads that where made later.

[speedytinc]

They are the ones labeled 8-1. A little misleading as I’ve heard they are closer to 5.5-1 or so. Someone may correct me. Mine has a “P” near the water outlet.

You are correct. The Prus head has slightly more compression than the Z & is much better quality. I highly recommend Prus.
Really adds more zip to a T motor.

[Philip]

i am running the z head and it works great. i have had no quality or head gasket issues. philip

[Ruxstel24]

I’m running a Jensen aluminum head...
It is actually THE head Kevin Prus used to make the mold for his heads. Before the Ford script legalities, so it has the script.
Definitely has more zip than a Z head.
A Z was on it before for years, but had cracked after the garage heater failed. My father had passed away and he had water in the system and I was not aware that the heater was broken.

[speedytinc]

i am running the z head and it works great. i have had no quality or head gasket issues. philip

All 3 of the Z heads I have dealt with have had randomly inconsistent combustion chambers & required combustion chamber re machining.
The one I ran for years developed really bad corrosion issues. That my have been my fault. The Prus head claims to be sealed with a modern aluminum head process to prevent corrosion & the combustion chambers are spot on.
I am glad you have a good Z head.

[babychadwick]

Im using a Sherman on the speedster I'm building. Something of importance to consider is if you are seeking to simply get more power you may get better results with a carb and cam with a stock low head then investing in a head. Of course if you do all 3 thats different. My personal favorite for simplicity is HC head, sidedraft stromberg, inverted vaporizer intake and model A cam with a dist. You can still run a stock exhaust and aside from the cam it's all just bolt on.

shiney.jpg (36.03 KiB) Viewed 6504 times

[Bruce Compton]

I've used both the "Z" head and the Prus head and the Prus performs slightly better and certainly seals better in the areas where the cylinders are only less that 1/4" apart. My Z head set-up had head gasket failures in this area twice whereas the Prus head has more material (wider) in this area and I've had zero problems with it. Either way, they are without doubt the best "bang for the buck" you can get for your "T", and the next being an aftermarket carb like a Stromberg OF or RF, or a Wheeler-Schebler FAX8.

[AndyClary]

I will second what John said about inconsistencies in the Z head chambers. It is rare not to have to machine for piston clearance. I have not used a Prus head but I understand that it is a better casting. He has advertisements in the club magazines.

Andy

[JBog]

So then, regardless of which option a person chooses, do they still need to have the "head saver" installed in the coolant system? If so, does that mean you need to flush corroded aluminum out from time to time?

[Ruxstel24]

So then, regardless of which option a person chooses, do they still need to have the "head saver" installed in the coolant system? If so, does that mean you need to flush corroded aluminum out from time to time?

The Prus head is available in iron....
You should change your coolant every 3 years regardless. I don’t run an anode in mine.

[speedytinc]

So then, regardless of which option a person chooses, do they still need to have the "head saver" installed in the coolant system? If so, does that mean you need to flush corroded aluminum out from time to time?

The Prus head is available in iron....
You should change your coolant every 3 years regardless. I don’t run an anode in mine.

Unfortunately, Prus doesnt offer an iron head & according to them, they wont due to casting porosity problems when thy did.

I ran an anode in my Z head. Still rotted out. Never had any head gasket issues.

[Ruxstel24]

So then, regardless of which option a person chooses, do they still need to have the "head saver" installed in the coolant system? If so, does that mean you need to flush corroded aluminum out from time to time?

The Prus head is available in iron....
You should change your coolant every 3 years regardless. I don’t run an anode in mine.

Unfortunately, Prus doesnt offer an iron head & according to them, they wont due to casting porosity problems when thy did.

I ran an anode in my Z head. Still rotted out. Never had any head gasket issues.

Did not know Kevin stopped the iron production.

[Norman Kling]

If you run a high compression head, be sure not to lug the engine because it would be hard on the crankshaft. Going uphill, keep it revved up. If it slows down, gear down so it doesn't lug.
Norm

[Hudson29]

I do not believe the anode is a good idea. I ran one for some years on a Z head and it filled the cooling system with a sort of greyish crudula. After an overhaul the green anti-freeze was used and the system has stayed clean & cool ever since.

I like the Z head. It was on the car when I bought it and I have no idea how much, if any, work might have been needed to make it fit. I had it surfaced during the overhaul and it still works fine. One purely visual thing. It looks like a stock Ford head. The only way to tell its not stock is to see the little Z cast in near the water outlet. It does say Ford right where the factory ones do.

Paul

[Mark Gregush]

The Z head I put on a friend's 26 coupe, did nothing but install it.(I did check for clearance first after reading all the posts) He likes the extra power it gives. I would suggest getting the one for stock plugs. If you want to run 14mm, you can add adapters.

[speedytinc]

The Z head I put on a friend's 26 coupe, did nothing but install it.(I did check for clearance first after reading all the posts) He likes the extra power it gives. I would suggest getting the one for stock plugs. If you want to run 14mm, you can add adapters.

Yes, you got lucky in that respect, but did you check the volume of each combustion chamber? They typically vary all over. Not ideal.
Critical? Probably not.

[TRDxB2]

Good place to learn about Head Design http://mtfctulsa.com/Tech/head_design.htm and other Model T tech
http://mtfctulsa.com/Tech/head_dyno_testing.htm
http://mtfctulsa.com/Tech/index.htm

[JBog]

Good place to learn about Head Design http://mtfctulsa.com/Tech/head_design.htm and other Model T tech
http://mtfctulsa.com/Tech/head_dyno_testing.htm
http://mtfctulsa.com/Tech/index.htm

I don't see the Prus on this chart. How does it compare to the Z head?

[speedytinc]

Good place to learn about Head Design http://mtfctulsa.com/Tech/head_design.htm and other Model T tech
http://mtfctulsa.com/Tech/head_dyno_testing.htm
http://mtfctulsa.com/Tech/index.htm

I don't see the Prus on this chart. How does it compare to the Z head?

Prus is a little bit higher. The CC numbers I have are not with me now.

[TXGOAT2]

Flathead engines have limits as to how high compression can be raised. You have a high volume combustion chamber to begin with, and at some point, milling the head will begin to restrict flow between the area where the valves are located and the cylinder proper. They are generally more prone to detonation at higher compression levels also, due to the size and conmformation of the combustion chamber. Good engineering can offset these drawbacks to some degree but limitations remain. There are good reasons why early hot rodders went so far as to adapt or design and produce overhead valve equipment for early Fords. I believe that overhead valve conversions were available for the flathead V8s, too.

[Mark Gregush]

The Z head I put on a friend's 26 coupe, did nothing but install it.(I did check for clearance first after reading all the posts) He likes the extra power it gives. I would suggest getting the one for stock plugs. If you want to run 14mm, you can add adapters.

Yes, you got lucky in that respect, but did you check the volume of each combustion chamber? They typically vary all over. Not ideal.
Critical? Probably not.

Re the CC; personally I don't see the need on a car that is going a top speed of 35 maybe 40. Some of these things, like cc'ing a head for the average T owner, might just be overkill.

[Been Here Before]

If I may make a suggestion...Tuning a side valve T motor... please review stuff like:
https://www.mig-welding.co.uk/forum/thr ... lve.72820/

[speedytinc]

The Z head I put on a friend's 26 coupe, did nothing but install it.(I did check for clearance first after reading all the posts) He likes the extra power it gives. I would suggest getting the one for stock plugs. If you want to run 14mm, you can add adapters.

Yes, you got lucky in that respect, but did you check the volume of each combustion chamber? They typically vary all over. Not ideal.
Critical? Probably not.

Re the CC; personally I don't see the need on a car that is going a top speed of 35 maybe 40. Some of these things, like cc'ing a head for the average T owner, might just be overkill.

CCing a Z head is to be able to get the combustion chambers of the same displacement to fix em. The uneven forces of 4 different cylinder pressures cant be healthy on a T crank. Depending on how far off. Secondly the #s give a reference of & between different heads.
For a T thats driven @ 35, the extra horse power will flatten out steep hills. You dont have to drive fast for benefits.
CCing a head is a very simple operation. Anybody can. A head like the Prus is made to hi quality standards, the #'s are just a reference point. I CC'd the Pruis head to determine the actual compression ratio & for comparison to other heads. If the actual compression was 8:1, as claimed, i wouldnt run it.
The average guy can slap a Prus head on & be confident there's no issues without CCing it. I needed to prove it for myself. Trust but verify.
Many of my customers want a performance boost. I can confidently recommend it. Not to say other heads are not as good. I have not checked em all.

[TXGOAT2]

Ccing chambers can get you a smoother running engine. It can allow determining if a chamber or two is oversize, which might then be corrected by milling the head then machining the other chambers to match. A smooth idle and good low speed characteristics are one benefit of uniform chambers. Another might be less vibration and stress on the crankshaft at certain higher speeds and loads. Uniform chamber size might improve the performance of a performance intake and a performance cam might be expected to give better results. Having all 4 cylinders performing at their best is one way to maximize power, durability, and driveability, whether an engine is built to stock spec or built for some higher than stock level of performance, be it torque for a TT or horsepower for a speedster or anything in between.

[speedytinc]

Good place to learn about Head Design http://mtfctulsa.com/Tech/head_design.htm and other Model T tech
http://mtfctulsa.com/Tech/head_dyno_testing.htm
http://mtfctulsa.com/Tech/index.htm

I don't see the Prus on this chart. How does it compare to the Z head?

CC's on the Z head I ran (after re-machining 3 combustion chambers) was 223 5.4-1 They can vary a bunch.
Prus head CC'd @ 220 5.38-1

[JBog]

Good place to learn about Head Design http://mtfctulsa.com/Tech/head_design.htm and other Model T tech
http://mtfctulsa.com/Tech/head_dyno_testing.htm
http://mtfctulsa.com/Tech/index.htm

I don't see the Prus on this chart. How does it compare to the Z head?

CC's on the Z head I ran (after re-machining 3 combustion chambers) was 223 5.4-1 They can vary a bunch.
Prus head CC'd @ 220 5.38-1

So it sounds like the two are close, but the Prus is better quality from the outset.

[bobt]

I installed a Prus head on my 26 roadster and had to remove it because the pistons were hitting the head. I found out that my block was bored .80 over. Mr. Prus told me to remove material from the sides of the pistons. I'm thinking of removing material from the head itself. Comments? Ideas? I put my Z head back on that blows a head gasket every two years. I'm guessing that the previous owner removed too much material from the Z head. Thanks, bobt

[TXGOAT2]

Pistons are cheaper than heads. I'd be inclined to follow Mr. Prus's advice and modify the pistons. I'd want to avoid taking much material off, and I'd want all pistons to match in weight and contour. A different style set of pistons might be a solution to consider.Your block may have been decked, and you could have a rod that is longer than it should be due to the way it was rebabbited. Well-worn main bearings will raise the crankshaft a little. It may be that different style head gaskets will give a different installed height. I'd also want to know what the minimum required clearance is.

[Norman Kling]

If the block is .80 over, it is possible for the pistons to hit even a stock head. Usually somewhere the edge of the piston touches the head. It's time to sleeve the block back to standard.
Norm

[TXGOAT2]

Mr. Kling makes a good point. Boring out past .060 reduces the already marginal sealing surface. It also tends to cause more heat to be dumped into the water jacket rather than out the exhaust, which can make for a hot running engine. Core shift may become an issue. In the case of Model T engines, corrosion has likely reduced the wall thickness throughout the engine. A good sleeve job takes most of these potential problems off the table. I'd avoid boring past .060 on an old engine. .040 might be a better limit in an very old engine. Ford used steel sleeves in the N-Series tractors and some of the V8s. If available, steel sleeves might be a good choice for use in an old block.

[speedytinc]

Pistons are cheaper than heads. I'd be inclined to follow Mr. Prus's advice and modify the pistons. I'd want to avoid taking much material off, and I'd want all pistons to match in weight and contour. A different style set of pistons might be a solution to consider.Your block may have been decked, and you could have a rod that is longer than it should be due to the way it was rebabbited. Well-worn main bearings will raise the crankshaft a little. It may be that different style head gaskets will give a different installed height. I'd also want to know what the minimum required clearance is.

I agree with cutting the OD of the pistons above the top ring grove. Cutting the head for clearance invites head gasket issues. That would be a second best fix over a sleeve job to keep this motor in service, unless you are having overheating/water jacket issues. If the motor is out or going to be pulled to fix the pistons anyway, sleeve it now.