Iron vs. aluminum head compression

[Vanspeed]

Looking at getting just a little more power out of my 36 LB and I was looking at Vanpelt’s site. It lists compression ratios but for a ‘36 it only lists aluminum heads. My engine has cast iron heads on it. Were the cast iron and aluminum heads this year the same compression ratio? I noticed for the ‘37 they are different.

[cjshaker]

It's strictly my opinion, but when dealing with compression ratios, you're throwing darts unless you actually CC the heads and block area. These engines are old, and who knows how many times, or how much, the block and heads have been surfaced. If your iron heads have been shaved a couple of times over its lifespan, it's entirely possible that you could be dropping compression by moving to another set of heads. At a minimum, your iron heads should be CC'd to figure out where they stand, then you can make a more informed choice. Or you could simply have your heads shaved to up the compression (cheaper than new heads), but careful measurements must be taken to make sure there won't be an issue with piston/valve to head interference, or that you're not getting into 'detonation' territory.

[Ol' Ron]

Some of the early aluminum heads were the "Denver" HI compression heads that had aprox one point higher than stock
Gramps

[Model51]

Ford Canada claimed the 1935-1936 V-8 engines with aluminum heads had higher compression resulting in 10% power increase over the cast iron heads. They claimed the aluminum head version was 90 HP and the cast iron version was 80 HP (actually 82 HP if you read the Ford literature details). I have no way to verify these claims by Ford of Canada but that's what they told the customers.
I think that improving the horsepower of your engine will take some study and measurements especially if you are only using "bolt-on" replacement parts. Heads get milled down or ported, bores increase, etc. Also, without pulling the motor and testing on a dyno, is there a way to measure any improvement? Just wondering.

[Seth Swoboda]

What are you wanting to achieve with "more power". Are you looking for more low end torque? Are you wanting more power for highway cruising? Give us a little more desrcription on what your end goal is and we'll throw ya a bunch of opinions.

[wamnram]

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The aluminum heads have a higher compression ratio than the cast iron heads. This is true for both the 48 series and 68 series heads usually found on the 36 model engines. Both heads list CR of 7.52 for aluminum and 6.06 for cast iron with stock bores. 40 series heads are 6.5 aluminum and 5.42 for Cast Iron.

[Vanspeed]

I live in a very hilly area. Just moved here about a year ago. So glad I have an 8 now in my Model A. It never would have made it on these hills. That being said, I would like to maintain a more constant mph over the hills if possible. I also have some hot rod blood in me and vintage speed equipment is not ugly, in my opinion.

The engine is .030 over, was a very good running engine. Saw the car with this engine in it before it was pulled to build a street rod. Stock cam, stock intake with an English stromberg. Bubbas crab distributor, iron heads and headers I built.

End goal, have it stay in its power band the whole time. It tends to fall on its face in third if I stretch her legs. Also maintain speed over hills are rather tall.

Originally Posted by Seth Swoboda

What are you wanting to achieve with "more power". Are you looking for more low end torque? Are you wanting more power for highway cruising? Give us a little more desrcription on what your end goal is and we'll throw ya a bunch of opinions.

[Vanspeed]

This is the car it is in. It’s a ‘29 coupe which should be rather light?

[Seth Swoboda]

Yes, a V8 should make that coupe fly. A set of Offenhauser or Edelbrock aluminum heads and a mercury 4 inch crankshaft paired with a compatible camshaft should be more than enough to make your Model A with a 3.78? rear end go over hills.

[Vanspeed]

Originally Posted by Seth Swoboda

Yes, a V8 should make that coupe fly. A set of Offenhauser or Edelbrock aluminum heads and a mercury 4 inch crankshaft paired with a compatible camshaft should be more than enough to make your Model A with a 3.78? rear end go over hills.

Heads are limited because it is an early 21 stud. It is a ‘36 LB. Sharp heads are the only available at the moment. I think I have a 3:78 rear. It is bone stock and I think most A’s came factory with them. I can run cruise at 65, had it up to 85 once, lol.

[Ol' Ron]

CONSIDERING THE FACT THESE NUMBERS ARE "factory" I'd refer you t jowl's book. The 239ci flathead had 79 HP, and nonmetered what you did to the 239 engine, hecouldn't get 100hp from it. so i doubt ant HP clams from the "Factory" Read the book!
Gramps