cast iron or aluminum heads? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mwilliams5891 · 10-10-2010, 10:49 PM

So I picked up a freshly rebuilt 327 short block yesterday

and was turned on to some great heads by a friend on here and they have them in cast iron and aluminum. i'm not building a race truck but i'd like to get some good HP out of that little motor. so does anyone know how much more power ill get if i upgrade or if its worth it?

thanks a million guys

oh and if anyone knows where i could get a used tremec 5 speed for that 327 that would be great...also if anyone has advice about that 327 build up let me know

Kerry P · 10-10-2010, 11:39 PM

The material (Aluminum or Iron) is not the primary factory in determining the performance characteristics of a head. It's all about port and chamber design. If the two heads you are looking at are the same physical design, they should perform about the same. Aluminum heads do tend to tolerate a little more compression than their iron counterparts. In theory the faster heat dissipation of aluminum heads may actually lower their output compared to identical iron heads. Most dyno testing does not find much difference based on just iron vs. aluminum though.

One thing in iron's favor is then the heads have the same thermal expansion as the block. This puts less stress on the head gaskets.

If you are not exceeding about .475" lift at the valves, Vortec heads are hard to beat. Sounds like you will need an intake manifold so the fact that Vortecs need a specific intake won't be much of an added expense if you were buying a new one.

I would not try for over about 375 flywheel HP with a 327 in a truck. It is easy to lose low end torque when getting too much HP from a smaller small block. Even at 375 HP it might be "soft" in everyday driving without adequate gearing.

Sounds like you have a good start. Putting parts on a good short block is the fun part of a build up

Kerry P

llowlife · 10-10-2010, 11:53 PM

What heads are they? Depends on your budget typically aluminum heads are easier to machine so can flow better. THey are much lighter and you can run a point or so higher compression as a rule of thumb. That being said I have CI on my motor and am not disappointed. CI retains heat better so less is lost to the cooling system. Higher powers than me have said that all things being equal a CI will eek out a bit more torque. But with the ease of machining all things will not be equal.

What are you planning to accomplish with your 327? Typically you need to twist them a little tighter so as always (even more so) you need to build a good solid shortblock. Ooops sorry just remembered you already have a shortblock. Please come back here after you have decided on a cam.

llowlife · 10-10-2010, 11:55 PM

Wow I should have read Kerry P's post and saved myself the trouble of slow typing. Said basically the same exact thing

Oh yeah...what pistons are in her? FT. Domes? Hypers? forged? Head decision may be based on these answers as well

10-10-2010, 10:49 PM	#1
mwilliams5891 Registered User Join Date: Aug 2010 Location: Springfield, Oregon Posts: 164	cast iron or aluminum heads? So I picked up a freshly rebuilt 327 short block yesterday and was turned on to some great heads by a friend on here and they have them in cast iron and aluminum. i'm not building a race truck but i'd like to get some good HP out of that little motor. so does anyone know how much more power ill get if i upgrade or if its worth it? thanks a million guys oh and if anyone knows where i could get a used tremec 5 speed for that 327 that would be great...also if anyone has advice about that 327 build up let me know

10-10-2010, 11:39 PM	#2
Kerry P Registered User Join Date: Aug 2010 Location: Harrison Arkansas Posts: 164	Re: cast iron or aluminum heads? The material (Aluminum or Iron) is not the primary factory in determining the performance characteristics of a head. It's all about port and chamber design. If the two heads you are looking at are the same physical design, they should perform about the same. Aluminum heads do tend to tolerate a little more compression than their iron counterparts. In theory the faster heat dissipation of aluminum heads may actually lower their output compared to identical iron heads. Most dyno testing does not find much difference based on just iron vs. aluminum though. One thing in iron's favor is then the heads have the same thermal expansion as the block. This puts less stress on the head gaskets. If you are not exceeding about .475" lift at the valves, Vortec heads are hard to beat. Sounds like you will need an intake manifold so the fact that Vortecs need a specific intake won't be much of an added expense if you were buying a new one. I would not try for over about 375 flywheel HP with a 327 in a truck. It is easy to lose low end torque when getting too much HP from a smaller small block. Even at 375 HP it might be "soft" in everyday driving without adequate gearing. Sounds like you have a good start. Putting parts on a good short block is the fun part of a build up Kerry P

10-10-2010, 11:53 PM	#3
llowlife Registered User Join Date: Jan 2010 Location: Elgin Mn Posts: 112	Re: cast iron or aluminum heads? What heads are they? Depends on your budget typically aluminum heads are easier to machine so can flow better. THey are much lighter and you can run a point or so higher compression as a rule of thumb. That being said I have CI on my motor and am not disappointed. CI retains heat better so less is lost to the cooling system. Higher powers than me have said that all things being equal a CI will eek out a bit more torque. But with the ease of machining all things will not be equal. What are you planning to accomplish with your 327? Typically you need to twist them a little tighter so as always (even more so) you need to build a good solid shortblock. Ooops sorry just remembered you already have a shortblock. Please come back here after you have decided on a cam. __________________ In the beginning of a change, the patriot is a scarce man, brave hated and scorned. When his cause succeeds however, the timid join him , for then it costs nothing to be a patriot. I am a revolutionary...so my son can be a farmer...so his son can be a poet. If there must be trouble, let it be in my day, so my child may have peace... 72 short step w/ 388 /4l80e/ and 3.08 gears.

10-10-2010, 11:55 PM	#4
llowlife Registered User Join Date: Jan 2010 Location: Elgin Mn Posts: 112	Re: cast iron or aluminum heads? Wow I should have read Kerry P's post and saved myself the trouble of slow typing. Said basically the same exact thing Oh yeah...what pistons are in her? FT. Domes? Hypers? forged? Head decision may be based on these answers as well __________________ In the beginning of a change, the patriot is a scarce man, brave hated and scorned. When his cause succeeds however, the timid join him , for then it costs nothing to be a patriot. I am a revolutionary...so my son can be a farmer...so his son can be a poet. If there must be trouble, let it be in my day, so my child may have peace... 72 short step w/ 388 /4l80e/ and 3.08 gears. Last edited by llowlife; 10-10-2010 at 11:59 PM.



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