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Iron vs. Aluminum Heads

In a perfect world, this would be a story about our stupid Disco Nova, but since that fell through again, we sought the truth about iron vs. aluminum aeads

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Can you guess what we learned? Zilcho. As in zero difference anywhere in the power or detonation characteristics of the iron versus aluminum heads. Even the optimum total ignition timing was the same at 36 degrees. Regardless of coolant temp, rate of acceleration, steady state, or through a sweep, the dyno curves for the two styles of heads were identical. If anything, we could squint and guess and mumble that maybe aluminum heads were better by 2-3 hp. But the one thing we could never say is that the iron heads retained more heat and made more power than the aluminum. Maybe it's different on some engines with a drastically different water-jacket design, but we'll stand up and say that the old bench-racing line just ain't true.

We're not going to be quite so cocky about debunking the claim that you can run higher compression on pump gas with aluminum than with iron. Our test does not definitively prove that. It may not have even tested it. We can say with complete confidence that we did not encounter detonation at any point during our testing, even at 10.88:1 compression. That could be because the cam was pretty big, with an intake-closing point 79 degrees ABDC. With cranking compression in the 185s, it was not taxing the detonation point even with 91 octane. Also, the Engine Masters thing has pretty well demonstrated that a dyno seems to have far more detonation tolerance than do actual driving conditions in a car. So, ultimately, we don't think we pushed that limit enough to make a positive finding.

Still, that's one bench-race axiom that's still up for grabs and another one chucked out the door. Not bad for page filler.

Head Flow Test Data
All testing was done on a 4.030-inch bore fixture and at 28 inches of pressure drop. A flow tube with 1 3/4-inch diameter was used on the exhaust side.
 IronAluminum
LIFTINEXINEX
0.05031253123
0.10065546457
0.200121109127105
0.300165138174138
0.400213168213169
0.500242185242182
0.600258192250189
The Power
These charts reveal the STP-corrected power curves for the 388. Both curves are with the aluminum heads, but the curves for the iron heads are identical, give or take a number here and there. These two columns reveal the difference in power when the dyno pull is made starting with a coolant temp of 110 degrees versus 185 degrees. Heat kills power.
 110 DEG. F185 DEG. F
RPMLB-FTHPLB-FTHP
3,000410234393225
3,100413244393232
3,200414252394240
3,300415261396249
3,400416269397257
3,500418279398266
3,600422289401275
3,700427301405285
3,800431312407295
3,900435323411305
4,000438334416317
4,100445347422330
4,200451361430344
4,300458375436357
4,400465389442370
4,500471403448384
4,600475416453397
4,700478428456408
4,800480439458419
4,900481449460429
5,000481458461439
5,100480466460446
5,200476472457453
5,300472476454458
5,400468481450463
5,500464486447468
5,600460490442471
5,700455493437474
5,800450497432477
5,900444499427480
6,000438500421481
6,100432502415483
6,200425501408482
6,300416499401481
6,400410500394480
6,500402497387479
SOURCES
Dart Machinery
353 Oliver St.
Troy
MI  48084
248-362-1188
www.dartheads.com
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1 comments
Dylan Hutchison
Dylan Hutchison

So basically the difference is just the pros and cons of the material itself,

Iron heads you can work on without worrying about scratching or dinging up.

But aluminum heads take the win because there lighter, less prone to cracking when getting hot, and dont rust.

Aluminum is what ill stick with for now!

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