Iron Head/Alum Heads
 

Is there a significant difference in pwer between the two? I mean is 20 horsepower worth the difference in price for a weekend warrior?

There really isn't much in the area of a power difference. Fact is, many companies design they're cast iron and aluminum heads slightly differently. Even if they have the same name. For instance, the FMS GT-40 iron heads are at a disadvantage to the GT-40 aluminum heads due to revised ports and whatnot on the aluminums. The biggest differences is that aluminum disapates heat faster and weighs considerably less than iron.

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1984 1/2 GT350 (#842 Hatchback w/ T-tops), 302HO, Comp cams Xtreme Energy cam, Carter 625cfm carb, Weiand Stealth intake, MSD distributor, MSD coil, FMS 9mm wires, 1 5/8" MAC unequal shorties, 2 1/2" MAC Prochamber H-pipe, Flowmaster 2 chambers, KYBs, 16"x8" 4 lug Cobra Rs, Falken 245/45ZR16s

Hey, this is briefly discussed at Mustang Works, Articals/Powertrain/Cylinder Head Science.


"Alum. Vs. Cast Iron
Given a 9:1 or 10:1 compression ratio
(static) an Iron Cylinder will make more
horsepower than an Aluminum head, due
to the fact that it retains heat
(power/energy) more efficiently. However,
Aluminum is lighter, easier to work with
(and cheaper to produce), and more easily
repaired. In addition, Aluminum is more
resistant to detonation under high
compression, nitrous or boost situations."
http://www.mustangworks.com/articles...adScience.html

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'79 Mustang Coup
4" Cowl
Weld wheels (15x6;15x8)
Stock 5.8L
C4 w/ shift kit
1.5" MAC full length headers
Holley 750 CFM
Edelbrock intake
2.5" Off road H-pipe, 2-chamber Flowmasters
8.8" Rear end w/ 3.55 gears (Now that's more like it!!) http://www.mustangworks.com/msgboard/biggrin.gif
Front: 225/60/15 Rear: 255/60/15 Eagle GT II
14 x 4” K&N air filter (getting the Xtreme setup soon) http://www.mustangworks.com/msgboard/cool.gif

"Red, thou art my companion. Hasten now your quickened metamorphosis to Green that I may conquer all
who dare abide there beside me. May they be left thither behind burnt black." ---Fox Body

Yeah, I was gonna say that all things being equal an iron head will make more power since there is less heat rejection.

another consideration is that aluminum heads due to their dissipation of heat can handle a higher compression ratio with crap gas than iron heads, so you can run the same gas with a higher compression ratio. If you have the money, i'd recommend you get the aluminum heads especially if you're going to modify the bottom end or add forced induction. One problem though, due to dissimilar metals is that the head gaskets are more likely to fail if you don't regularly change the coolant (due to the engine grounding the spark, the coolant reacts to the electrical current and becomes acidic which eats a path through the gasket sealing surface. With dissimilar metals the heating and expansion of the metals can stress different parts of the gasket or even cause an opening. If you don't change your coolant often enough, you can hook up a multimeter (Volts) and see the coolant holding a charge - i've seen it, it's damn weird!)