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Old 11-06-2008, 07:45 AM
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SBC Heads. Alum or Cast??

Besides the wieght advantage, is there any other advantage to running a set of aluminum heads over a good set of iron heads??

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Old 11-06-2008, 08:11 AM
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Heat dissapation with aluminum is greater thus allowing higher compression ratios- generally in the range of 1 full point over iron.
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Old 11-06-2008, 10:50 AM
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Quote:
Originally Posted by Stonebrier 2
Besides the wieght advantage, is there any other advantage to running a set of aluminum heads over a good set of iron heads??
Proabably not in so far as power is concerned. The two big advantages are weight reduction and reapirability if something inside breaks and the combustion chamber gets beat up, or ease of modification to the ports which can be changed big time with some aluminum plate or tube and a welder.

However, aluminum has a faster heat trasfer rate, with no other changes against a cast iron head of equal compression ratio the power output would drop a little with the aluminum head. But because of the heat trasfer rate the compression ratio can be raised to and beyond the point of making equal power against cast iron without entering into detonation. So aluminum heads become another tuning medium for serious racers as you can juggle compression and engine operating temps to easily get, or drop, or change an engine's power characteristics and amounts for the weather and track conditions.

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Old 11-06-2008, 07:23 PM
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Which begs the question: Does making the head out of aluminum ALLOW a higher compression ratio, or does it REQUIRE a higher CR?
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Old 11-06-2008, 07:37 PM
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Quote:
Originally Posted by jimfulco
Which begs the question: Does making the head out of aluminum ALLOW a higher compression ratio, or does it REQUIRE a higher CR?

The head material doesn't really allow or require a different compression- it has more to do with the chamber finish. aluminum chambers have a smoother finish- unless the cast chambers are CNC'd.
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Old 11-06-2008, 09:13 PM
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It doesn't matter how you look at it... requiring or allowing. Some will say that it requires the extra compression to regain the heat loss of aluminum, while others view it as a way to get a little more compression to match a cam without having to use higher octane.

The chamber finish does have some to do with it, but if you polish iron chambers, you can't just magically add 1 full point of compression. Its mostly to do with the speed at which aluminum absorbs and transfers heat.

Either way, power differences are not really measurable, and adding compression alone will only add very small amounts of hp. I consider aluminum a benefit only for these two advantages: less weight, and softer metal is easier to port.

Many magazines and build shops have done apples-to-apples comparisons with the same casting that comes in either aluminum or iron. Outputs were identical in every way with only 2-3 hp differences which could be attributed to core shift, casting flash, production tolerances, or just the fact that back to back dynos don't produce the same numbers all the time.
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