MTFCA Forum

Posted: **Wed Sep 22, 2021 5:41 pm**

Hi All,
I have just been looking at the high compression heads that are available, and they are listed as suitable for 1918-27 cars. My car is a 1915 tourer. Is there some reason which means the head won't fit in? Surely there is slightly more room with a lower head? Or am I missing something?

Many Thanks for any information you may be able to give.

George

Posted: **Wed Sep 22, 2021 5:46 pm**

I'm not savvy on those heads and what years they work on, but, unless you're not doing a rebuild, did you consider high compression pistons instead?

Posted: **Wed Sep 22, 2021 5:48 pm**

They fit OK, have one on a 16, just make sure to fit a new top hose as well to be soft enough for the alignment in height difference.

Posted: **Wed Sep 22, 2021 5:58 pm**

Thank you for your prompt replies, I have looked at the pistons too, but as I am not rebuilding the engine (it was rebuilt, along with the rest of the car, before I bought it) I thought the head might be an easier option, so long as it would fit. Are there any other advantages to the domed pistons over the head?

The main reason for all of this is I am looking into alternatives to a ruckstell or warford, to increase high climbing performance and also low speed drivability. Living in the U.K with narrow lanes etc, there are times when you can't have enough of a run at a hill at present to not have to change down into bottom gear and crawl up, and there are other times when a little extra power could be needed at slow speed, although I'm not really after increasing the top speed!

Posted: **Wed Sep 22, 2021 6:00 pm**

Sure, the high compression heads will fit on your ‘15..... but why? The original low heads for ‘15 increase HP by 10% over Ford’s later high heads.
And if you buy an expensive new HC head, you’ll also need longer head bolts.

Posted: **Wed Sep 22, 2021 7:00 pm**

George.
I have T's with both, high dome pistons are the cheaper way to go as far as parts go, labor is not an issue for me as all I do is rebuild T's, but the HC head (Z) will give more power. An E or I timer are great as well, even on a stock engine.

Posted: **Wed Sep 22, 2021 7:21 pm**

Kerry wrote: ↑
Wed Sep 22, 2021 7:00 pm
George.
I have T's with both, high dome pistons are the cheaper way to go as far as parts go, labor is not an issue for me as all I do is rebuild T's, but the HC head (Z) will give more power. An E or I timer are great as well, even on a stock engine.

First, look @ recent posts on the Prus head. It a little bit more compression than a Z head(despite the manufacturers wild claim) & far superior. Its physically based on a high head. I think there are low aluminum H/C heads available. No experience here. High dome pistons work with a high head. Not always with a low head. The domed pistons hit on my 14 with a milled head. Material had to be removed from the side opposite the valves to clear. Makes 95# compression. It do flatten hills pared with a Stipe 280 cam. Dont forget an upgraded cam. I am running a finely tuned new day With ECCT tuned coils. Runs real well.

Posted: **Wed Sep 22, 2021 8:08 pm**

I run the high compression pistons with a low head, it is a good combination. Unless a low head has been surfaced a lot there shouldn’t be a clearance issue. Yes, a high compression head will give a little more power, but no one is currently selling a high compression low head.

Andy

Posted: **Wed Sep 22, 2021 8:46 pm**

I like the improved performance of the high compression heads. I have used both the z head and the Pruis. To me, they both perform the same. The Pruis seems to be a better quality and has ample clearance for for piston travel. Just make sure the rods and mains are in good shape for the extra pressure. If they are not, you’ll find out any weak spots.

Posted: **Wed Sep 22, 2021 8:49 pm**

You must be careful not to push the engine too hard with higher compression. If you lug the engine, you run an increased risk of broken crankshaft. You already have a low head, which will give you more low end power than the high head. Do you know what kind of crankshaft you have? The SCAT crank is stronger than the earlier Ford cranks, and the later EE cranks are stronger than the earlier cranks.
Norm

Posted: **Wed Sep 22, 2021 10:48 pm**

I’ve been running domed pistons with stock low heads, on 5 or 6 engines, for years. I used to run aluminum HC low heads, but chose to go back to the cast iron heads with domed pistons and don’t see any degradation; it’s a great combination.

Posted: **Wed Sep 22, 2021 11:12 pm**

I agree with Tom.The Prus head has more meat between the cylinders than the Z head and also appears to be better finished (machined). I've run both as well as a Reeder head and the Prus runs best while the Z head has given me gasket problems twice in 1000 miles.

Posted: **Wed Sep 22, 2021 11:28 pm**

GeorgeHounslow wrote: ↑
Wed Sep 22, 2021 5:58 pm
Thank you for your prompt replies, I have looked at the pistons too, but as I am not rebuilding the engine (it was rebuilt, along with the rest of the car, before I bought it) I thought the head might be an easier option, so long as it would fit. Are there any other advantages to the domed pistons over the head?

The main reason for all of this is I am looking into alternatives to a ruckstell or warford, to increase high climbing performance and also low speed drivability. Living in the U.K with narrow lanes etc, there are times when you can't have enough of a run at a hill at present to not have to change down into bottom gear and crawl up, and there are other times when a little extra power could be needed at slow speed, although I'm not really after increasing the top speed!

What rear axle gear set is in your rear axle? Most came from the factory with 3.63 to 1 ratio gears, but 4 to 1 ratio gears were a factory option for hilly, mountainous, sandy, or muddy roads. The 4 to 1 ratio gears will probably cut 5 MPH off your top end, but greatly improve your low and mid range. Add high compression pistons, or head and you should be able to pull the hills with the best of them.

Posted: **Thu Sep 23, 2021 1:39 am**

I just completely rebuild an engine for a 1915. I to noticed that thePrus Head was listed for the newer engines. The only reason I think they say that is because it is based on the high cylinder head and would provide different aesthetics. I will tell you this, paired with a .280 cam and a scat crank my little roadster has no problems keeping up with city traffic. Plus I’ve seen an increase in MPG. I also was considering what I was hoping was better heat transfer in a brass radiator car. I think that might be the case but I cannot attest to that.

Posted: **Thu Sep 23, 2021 1:57 am**

There are many ways to increase engine performance. Carbonation, intake and exhaust manifolds, exhaust system, cams, pistons, high compression heads, crankshafts. and various combinations of them are needed to gain the bang for the buck. The Tulsa Club has a good article on High compression head and design https://mtfctulsa.com/Tech/heads.htm
The charts show that Torque is what gets you doing at low RPM and Horsepower is gives you a higher Top end speed. Unfortunately the results don't mention what other modifications where made besides swapping heads Clicking on the charts should make them larger

Posted: **Thu Sep 23, 2021 12:42 pm**

I went ahead and bought a Z head from Langs. They tell me it's back ordered 1-2 months. So whatever you decide, be prepared to wait for it.

Posted: **Thu Sep 23, 2021 12:57 pm**

I just received my second Prus High Compression head from Kevin Prus and must tell you I was thoroughly impressed with the performance on the first one.
Kevin had (18) of them in stock a couple weeks ago and I received mine at my door, two days after I ordered it. Same price as the Z Head, better machining and finish quality in my opinion and most guys will tell you they perform better. My two cents and I hope this helps.
Kind Regards,
Rick Rice

KEVIN PRUS (330)774-7130

Posted: **Thu Sep 23, 2021 1:32 pm**

I have a Z head on my '17 and am very happy with it. The fellow who rebuilt my engine had tested engines with both a Z head and a Prus and found they primarily differed in HP achieved at various RPMs. My Z head dynoed out at 25 HP at 1600 RPM which is a definite improvement over a stock T. Having no personal experience with a Prus, all I can say is that they have a great reputation for fit, finish and function.

FWIW - the fellow who makes the Z head has moved to Michigan since I bought mine. If they are unavailable from the vendors you might try going direct. My apologies to those offended that I'm suggesting buying from other than a big vendor. Be aware that copper head gaskets are hard to find which might interfere with a head swap.

Posted: **Thu Sep 23, 2021 2:24 pm**

Rick_Rice wrote: ↑
Thu Sep 23, 2021 12:57 pm
I just received my second Prus High Compression head from Kevin Prus and must tell you I was thoroughly impressed with the performance on the first one.
Kevin had (18) of them in stock a couple weeks ago and I received mine at my door, two days after I ordered it. Same price as the Z Head, better machining and finish quality in my opinion and most guys will tell you they perform better. My two cents and I hope this helps.
Kind Regards,
Rick Rice

KEVIN PRUS (330)774-7130

Does Kevin do email?

Posted: **Thu Sep 23, 2021 5:37 pm**

Along these lines, since these heads hold more coolant, do you need to add more coolant to the radiator?

Posted: **Thu Sep 23, 2021 6:42 pm**

George, I don’t think that a high compression head will keep you off the low band as much as you think. If you can’t get a run at a hill your speed pretty much dictates what gear you will use to climb. If you’re stuck going 10 mph you’ll still need to use low to keep from lugging the engine. Adding compression with lugging the engine is a bad combination.

Andy

Posted: **Thu Sep 23, 2021 7:26 pm**

A stock or mild cam and milled head might pull better at very low RPMs. Cam lift, duration, and timing can affect low end torque.

Posted: **Thu Sep 23, 2021 7:55 pm**

What sparkplug are you guys running in your high compression heads?

Posted: **Fri Sep 24, 2021 8:40 am**

TeveS-Nor Cal wrote: ↑
Thu Sep 23, 2021 7:55 pm
What sparkplug are you guys running in your high compression heads?

Cheap 1 piece champions, champion X & autolite platinum long reach 14 mm.
If you need different heat range, go 14 mm. Datsun Z plugs are a good length for adapters.

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