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Old 12-16-2003, 02:25 PM
BCNU 64 nova's Avatar
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Question How much comp??

Just how much compression will I be able to run with todays poor octane gas? Will be running alum heads forged pistons and maybe some of that temp coating to lower temp in cylinders.

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Old 12-16-2003, 02:32 PM
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aluminum heads and the "correct camshaft" and you
can do 11 to 1. Iron heads no way...

Cstraub
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Old 12-16-2003, 02:45 PM
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Looking at an Engle EP25 hyd 236 @ 50 with 495 lift with 1.5 rockers.
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Old 12-16-2003, 02:48 PM
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on a 110 to 112 lobe sep that will blead off enough
compression to run 93 octane gas.

Cstraub
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Old 12-17-2003, 09:03 AM
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With all things being equal you can generally run 1 point more compression with aluminum heads. I agree about 11:1 is it on pump gas with aluminum heads. You need to make sure you have a good quench and enough cam.
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Old 12-17-2003, 10:55 AM
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Quote:
Originally posted by Cstraub
aluminum heads and the "correct camshaft" and you
can do 11 to 1. Iron heads no way...

Cstraub
Huh? The material has NOTHING to do with it. Iron heads would be better, and 11:1 might run on 93 octane. Aluminum, The only reason would be a better heat transfer, but that wont matter. Gasoline does'nt detonate because of hot cyl. walls or head temps. It detonates because it is being compressed.

There was an article to put this "aluminum is better" rumor to rest, I could dig it up if you'd like. Basicly they took the same engine, ran it high compression and swaped out the heads for each test (aluminum vs. Iron). In fact the Iron head showed MORE promise than the aluminum heads.

Last edited by 87442lover; 12-17-2003 at 11:03 AM.
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Old 12-17-2003, 11:21 AM
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Aluminum heads act as a "heat sink", they transfer the heat out of the combustion chamber , which is why aluminum headed engines usually bump their static compression ratio up a point- to compensate.
It's not a "better" situation?
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Old 12-17-2003, 12:34 PM
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Quote:
Originally posted by Crazy Mopar Guy
Aluminum heads act as a "heat sink", they transfer the heat out of the combustion chamber , which is why aluminum headed engines usually bump their static compression ratio up a point- to compensate.
It's not a "better" situation?
detonation caused by compression has nothing to do with material heat. I guess I will have to find that article.
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Old 12-17-2003, 01:27 PM
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I agree, once the engine is running the temps stay constant in the combustion area from what I have learned. Aluminum is lighter, that's its only main advantage. If the logic behind aluminum cooling was true then when you put aluminum heads and intake on your car, the temp would drop 20 degrees because it disapates heat better. THe amount of heat that can be carried away by one material being less dense than the other is not enough to carry enough of it away in the instant between combustion cycles to make a difference. I'm interested in this topic too, and if somebody can provide data to prove me wrong I'd appreciate it because it would give me an excuse to buy some aluminum heads for my car! Saving 50lbs is not enough for me...

K
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Old 12-17-2003, 01:47 PM
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Quote:
Originally posted by 87442lover
detonation caused by compression has nothing to do with material heat. I guess I will have to find that article.
I wasn't talking about detonation?
A higher compression ratio can be used with aluminum heads because the aluminum transfers the heat out of the combustion process. I'm talking static compression ratios, not detonation.

Quote:
Originally posted by killerformula
I agree, once the engine is running the temps stay constant in the combustion area from what I have learned. Aluminum is lighter, that's its only main advantage. If the logic behind aluminum cooling was true then when you put aluminum heads and intake on your car, the temp would drop 20 degrees because it disapates heat better. THe amount of heat that can be carried away by one material being less dense than the other is not enough to carry enough of it away in the instant between combustion cycles to make a difference. I'm interested in this topic too, and if somebody can provide data to prove me wrong I'd appreciate it because it would give me an excuse to buy some aluminum heads for my car! Saving 50lbs is not enough for me...

K
Aluminum dissipates heat faster.
When comparing two engines, iron head and aluminum head, the aluminum head engine's static compression ratio is usually raised by approx. 1 compression point to compensate for the higher heat transfer of the head.
COMBUSTION heat, not radiator heat.
I can find information links if you would like? Just use your search engine?

Here is one explanation I found that is worded well....

Did you know: Many people don't pay attention to the compression ratio when going from cast iron to aluminum heads. Fact is that if everything else was equal the cast iron head would make more power than an aluminum head. Cast iron heads doesn't absorb heat from the combustion process as fast at aluminum heads, therefore more heat is available to push the piston down. The way to get back the lost horsepower is to up the compression on the aluminum head. Typically you can run about a half to full point more compression with an aluminum head over the cast iron.

From the site http://www.speedworx.com/cgi-local/s...erformance.htm

As far as DETONATION goes, aluminum *can* prevent detonation when compared to iron, but not ALWAYS, obviously.


Aluminum heads also work to reduce detonation in a couple of different ways. Late-model heads offer a better combustion chamber design that requires less timing yet makes good power. Aluminum heads also transfer heat more quickly, which tends to reduce cylinder pressure slightly, perhaps allowing a slightly lower-octane fuel.

From http://www.kitcarmag.com/techarticles/65298/

Try Google search or Jeeves or whatever you prefer with "aluminum" "detonation" etc... for keywords?

Last edited by Crazy Mopar Guy; 12-17-2003 at 02:06 PM.
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Old 12-17-2003, 02:34 PM
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Thank you Mopar guy. . .and to further this detonation is not caused by compression, detonation is caused when excess fuel is not burnt in the previous igntion/power stroke and pre-ignite on the next intake stroke. A properly tuned engine will run with compression. I have 2 barrel iron stuff in the midwest running 15 to 1 on gas, yes its race gas.

As far as iron heads making more power. Won't argue.. Hell Cup would still run iron if they could. Pound for Pound iron will always make more power, with that said and iron block makes more then aluminum because it moves. Same with heads, aluminum heads grow also.

Cstraub
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Old 12-17-2003, 03:51 PM
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I see. I guess I'm mostly convinced, but following this evidence its easier and actually more efficient to use iron, eliminating my excuse to buy aluminum. Dart iron eagles for me then!

Doesn't much of the heat produced just demonstrate wasted energy?

Lastly, I think combustion heat and radiator heat are separate, but also one in the same. For example, you claim that aluminum heads carry the heat away from the combustion area (so less heat to make the molecules less violent and less resulting pressure so to compensate move compression up to produce more heat to = things out- got it.). But after the heat is carried away from the combustion area, where does it go? It should go toward the top of the heads and into the water jacket to be carried away. If that were true, however, then the resulting temperatures under the hood and in the radiator would be different wouldn't they? I guess my point is, the heat has to go somewhere if its being dissipated so quickly. Where is it going then?

K
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Old 12-17-2003, 03:58 PM
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Some of the transfered heat would go out the radiator, and probably not be noticed if the cooling system can handle it, which it should be able to unless the cooling system was marginal with iron heads. (Some goes into the oil, some into the ambient air in the engine compartment...) It's not a great amount of heat in the grand scheme of the cooling system.

I'm not in love with aluminum parts that have stainless fasteners in them anywhere. Without heli-coils, anti-seize, etc they are a true pain in the butt !!?!
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Old 12-17-2003, 04:03 PM
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Ok, so the only way you would see it is if you had a crappy cooling system to begin with. But doesn't this mean that iron heads stress your cooling and oiling system less than aluminum!? Wow, that sucks!

K
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Old 12-17-2003, 09:24 PM
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It is NOT possible to increase compression by slapping on heads made of aluminum. If the chamber sizes are the same, than the compression ratio will be the SAME. Dont take any of this personal BTW.

You can NOT gain 1 point in compression just by adding them. Detonaton is the reason you can not run higher compression with low octane gas. The gas combusts BECAUSE of the piston forcing it into a very small area. Gasoline is very unstable in atomized form and vaporized form.

I'll find that damn article and post it, but it will take me some time.

Again wall temp. and cyl. temp have NOTHING to do with detonation of the gas. The walls would have to be red hot to ignite gasoline. Aluminum heads will just make your engine about 50lbs lighter. That's it!

EDIT: One trick is to take either Iron heads, or aluminum heads and smooth the chambers out to keep the gas/air mix. stable while being compressed.
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