Raising compression

[Bryant]

Has anyone ever cut down a low compression cylinder head to raise the compression of there engine? Basically looking to see if it can be done and about how much you can reasonably take off with the stock pistons in it.

[Bruce Compton]

The problem is not the potential piston contact, but removing enough material from the head without weakening the structure around the water passages. I'll bet that thousands of heads have been milled down maybe 1/8" (0.125") safely but you still have basically a low compression head with a poorly shaped combustion chamber providing inadequate turbulence. In the long run, you're way better off buying an aluminum HC head like the Prus head that's designed to raise the compression as well as increase turbulence, and increase water (cooling) capacity too.

[AndyClary]

All you would end up doing is ruining a good head for no measurable improvement in performance.


Andy

[Bryant]

Thanks for the info! probably makes more since to put higher compression pistons in maybe? Iam starting the rebuild process and pondering the pros/cons. Is it worth raising the compression? Not building a race engine just trying for a little more power.

[greenacres36]

Race engine…..well they did / do race T’s. But seriously, I put a high compression head on both of my cars and feel that they are well worth the money. I’ve seen a significant increase in economy and power when I need it with a new high compression aluminum head. I also put in a high-performance cam shaft. I love the way the cars run now. I loved the way they ran before but for me having a little extra power is almost a safety benefit especially in town when you can pretty much keep up with traffic. Plus you gain a much more efficient combustion chamber.

That’s just me.

[TXGOAT2]

Most original T heads have already been resurfaced, perhaps several times. Most all of them have lost strength due to internal corrosion. As pointed out, the chamber design is not at all suited to getting the benefit of higher octane fuel available today. Compression is important, but it is one of several important combustion chamber design factors.

[Erik Barrett]

Don’t waste your time and ruin an early head. Just pony up and buy a Prus or Z head. They are the best bang for your buck available. You won’t notice any difference with a butchered low head.

[ModelTWoods]

In another post about this subject, someone posted that they ran domed high compression pistons WITH a low head, milled .125, and they said that the performance improvement could be felt and was worth it. While I doubt that person would say the improvement was equal to a Z or Prus head, I have no reason to doubt that the combination would not produce a noticeable result.

[Craig Leach]

Hi Bryant,
I'm going to assume you are asking about milling a low head? My experiance with milling T heads has been dismal at best. If I need to replace the pistons I go with high compression pistons. They are only a few dollars more. And don't seem to produce enough compression to to get you into the two piece crank club. But do give some improvement. Prus, Z, Recardo and other heads are very costly for a cheep SOB like me and give performance close to needing a EE crank, A crank or Scat crank to prevent membership in that club. If you are looking at milling a Prus or Z head I have not heard of good improvements doing that over the risk. If you have stock pistons and a low head consider selling the low head and getting a aftermarket high compression head that is probably what will give you the best bang for your buck.
Craig.

[Cap]

Dad put an OD Carb with a Aluminum Intake Manifold with a 280 Cam and Scat crank and E-Timer on the TT C Cab truck when he Rebuilt it about 15 years ago.

Performance was great.. we were able to pull hills in High Peddle, that required Lo Peddle before

I've taken the OD Carb off, as I could never keep it adjusted for Idle.. Put the NH back on.. Still pull the same hills in High, just not as well..

It still moves right along.. But the Starting and Idle in now like a T should be..

Cap

[TWrenn]

Thanks for the info! probably makes more since to put higher compression pistons in maybe? Iam starting the rebuild process and pondering the pros/cons. Is it worth raising the compression? Not building a race engine just trying for a little more power.

Yep.

[TXGOAT2]

Are any good high compression heads available today that have the Ford script and other lettering on them? I'd prefer a cast iron head to avoid any issues with gaskets, corrosion, and spark plug threads.

[Rich Bingham]

Since well before 1908 right up to the present moment, a vast array of automotive behemoths have been available for those desiring "a little more power" than what a Model T Ford can deliver. What is it that drives owner "tinkeritis" seeking ways to squeeze a tiny bit more power out of their Ts ?? In most cases, the "improved" replacement parts, alterations and fiddling result in a "net power gain" that exists mostly in the mind of the owner. Want more power ? For heaven's sake, why opt for a Model T ?? I don't get it.

[TXGOAT2]

One thing that makes raising compression attractive is that modern fuel, unlike what was commonly available in the T era, has more than sufficient octane equivalency to allow substantially higher compression than was practical then. The many advantages of higher compression, not to mention the additional advantages of Ricardo-type and similar chamber designs, are indisputable. There are no significant drawbacks to realizing these advantages, among which are easier starting, more power, better throttle response, reduced carbon deposition, and increased fuel economy. If the driver handles the vehicle properly, durability will not suffer, and may actually be enhanced. Anyone intending to run a Model T engine hard at high speeds often would be well advised to intstall a new, counterbalanced crankshaft and related parts, among sundry other modifications. The engine's side valve design limits how much you can raise compression, and it's difficult to get much over 6:1, if that, which is still quite low.

[speedytinc]

In another post about this subject, someone posted that they ran domed high compression pistons WITH a low head, milled .125, and they said that the performance improvement could be felt and was worth it. While I doubt that person would say the improvement was equal to a Z or Prus head, I have no reason to doubt that the combination would not produce a noticeable result.

I am one such person. Milled low head @ .100", & hi dome pistons. Pistons needed to be clearanced in back to clear.( opposite valves) Produces 95# compression. Runs very well. A little bit better than a Prus. Fit my goal of appearing bone stock. It should perform better than it does for the extra work involved. IMHO. Stock pistons & a Prus head are a great combination. The more efficient chamber design negates some of the need for higher compression. Hi domes in a stock, low head is a smaller performance improvement, but a good option to retain originality.
This is only the head side of the total package.

[speedytinc]

Are any good high compression heads available today that have the Ford script and other lettering on them? I'd prefer a cast iron head to avoid any issues with gaskets, corrosion, and spark plug threads.

Strongly consider high dome pistons with a stock or slightly milled high head. Added performance is noticeable. The typical late head doesnt seem to have as thick a base & are more crack prone, but heads are cheap & experimentation can be done. I do agree an iron head is preferred. The Prus head is treated/coated like modern aluminum heads & should not have the corrosion issues lesser heads have if treated properly.
6:1 is low, but a 50% increase to a T is huge in how well it runs, yet not so high to pound out the bearings. Good compromise.

[ModelTWoods]

Are any good high compression heads available today that have the Ford script and other lettering on them? I'd prefer a cast iron head to avoid any issues with gaskets, corrosion, and spark plug threads.

Pat, No new cast iron heads are being made, presently, regardless of whether they have Ford script, or not. Kevin Prus did make make some of his heads in early production that were cast out of iron, but according to what I know, he lost his iron foundry connection and hasn't found a replacement foundry that produces a satisfactory casting in iron. That is why he only advertises aluminum heads. Occasionally, a new, unused Reeder head, which like the Z head has Ford script, comes up for sale (i've seen on on Ebay from a seller in Oklahoma City, priced at $500.00), but Reeder heads, like Z heads were all aluminum.

[TXGOAT2]

I've read of people having issues with spark plugs seizing in aluminum heads on later model ('70s) engines. I believe the solution was adding a plated coating (Iridium?) to the plug threads to prevent corrosion/sticking. A steel insert kit to repair heads was available, as I recall. I wonder how long pipe threads in aluminum would hold up? If a person chose an aluminum head, would opting for a "modern" gasketed plug be a wise choice? As for milling a stock head, is there an original specification for the head thickness, say from the top of the bolt bosses to the gasket surface? (And how would you verify that the bosses had not had a cut taken off?)

[JBog]

I've read of people having issues with spark plugs seizing in aluminum heads on later model ('70s) engines. I believe the solution was adding a plated coating (Iridium?) to the plug threads to prevent corrosion/sticking. A steel insert kit to repair heads was available, as I recall. I wonder how long pipe threads in aluminum would hold up? If a person chose an aluminum head, would opting for a "modern" gasketed plug be a wise choice? As for milling a stock head, is there an original specification for the head thickness, say from the top of the bolt bosses to the gasket surface? (And how would you verify that the bosses had not had a cut taken off?)

A little bit of anti-seize on the plug's threads when you install it clears that issue up.

[John Codman]

I agree with Rich Bingham; if you want a car with more power then A 20 HP T, why start with a T? I have been a hot rodder for decades, and one of the oldest comments in hot rodding is that whatever you do to the top of the engine, you also have to do to the bottom. If you are going to increase compression or add a high-performance cam, you also need to add a better crankshaft and improve the lubrication. The only substitute for cubic inches is cubic money.

[John kuehn]

A Model T is just that and you can only do so much to one. If I was wanting to go faster and have a more reliable ‘modern ‘ car I would find something in the 32 to 48 Ford era. You can build a Model T hot rod that looks out of place in the hot rod world that’s really a Model T in name only. To me they just don’t look right. Kind of got off the subject matter but as always to each his own.

[Bryant]

Well thanks everyone for there insights on the subject. And for everyone that “doesn’t get it” the model t started with more compression and then lowered it due to substandard gasoline. Now that we don’t have that problem I don’t see what it would hurt to raise the compression back up. As I stated Iam not building a race engine just looking for a little more power/compression as I live in a mountainous area. And I chose a model T because I love them not to turn it into a hot rod. Sorry if I offended anyone for trying to hit 25hp

[TXGOAT2]

25 HP at 1800 and 100 ft lbs at 900 would be nice...

[AndyClary]

The bulk of the Model T “performance” accessories were not for speed but for hill climbing. You open up any properly running T on a flat road it will eventually go fast. In the hills the lack of power is more telling. Add in 4 people, their crap and all the stuff under the seat that you can’t leave home without, and a moderate hill gets pretty steep. Compression is your friend on a hill.

Andy

[John Codman]

The bulk of the Model T “performance” accessories were not for speed but for hill climbing. You open up any properly running T on a flat road it will eventually go fast. In the hills the lack of power is more telling. Add in 4 people, their crap and all the stuff under the seat that you can’t leave home without, and a moderate hill gets pretty steep. Compression is your friend on a hill.

Andy

... but if you are running a 90 plus year-old crankshaft (higher) compression is not your friend.

[Bryant]

If we keep going with this we could talk our selves out of running our 90+ year old cars and trade them in for modern safe reliable cars that won’t explode the second you “tinker” with them I feel confident if Iam rebuilding the engine to be very thorough with all off its components. The point of this topic was is it possible to cut down a low compression head to obtain a minimal amount of compression or try to find a higher compression head? Not to go down a rabbit hole full off opinion. Thanks to all that posted positive relevant information. Much appreciated!

[DHort]

Have you considered a RAJO from Chaffins?

[Bryant]

Have you considered a RAJO from Chaffins?

I have definitely thought about it! I think right now since the car needs everything refurbished I need to stick with a standard rebuild so I can get on the road. I’ve also thought after I get this one fixed up and start fiending for another I would love to do a speedster project

[speedytinc]

Have you considered a RAJO from Chaffins?

I have definitely thought about it! I think right now since the car needs everything refurbished I need to stick with a standard rebuild so I can get on the road. I’ve also thought after I get this one fixed up and start fiending for another I would love to do a speedster project

Believe it or not, you can do a whole lot with a flat head. My first got upgraded over time to a Gemsa flat head +++She easily does 70 with great acceleration in a touring. Beat my share of over carburated rajo's. This takes a lot of modification & money. The thing to do is what you have in mind to build a warm driver. Then start building a hotter replacement motor with all the right stuff. Start with a Scatt crank. Save them pennies.

[TXGOAT2]

I believe that running a counterbalanced crank and aluminum pistons at the stock bore and stroke will free up several horsepower compared to a totally stock engine.

[Bryant]

Iam looking thru my Lang’s catalog now thinking Iam gonna need a lot of pennies! I guess time will tell. My goal was 5 years so hopefully she will be in good shape for her 100th birthday