steel vs aluminum heads. is steel better?

Posted By: dirt

steel vs aluminum heads. is steel better? - 07/01/09 12:26 PM

If you had 2 sets of heads , 1 steel and 1 aluminum and all other things between them were equal would the steel or aluminum make more power ?
I was thinking that the aluminum would need more compression to make the same power as the steel , is this true? I have heard you can run 1 point more compression with aluminum but isint it that you would need to run 1 point more to keep the same power?

Posted By: JohnRR

Re: steel vs aluminum heads. is steel better? - 07/01/09 01:44 PM

The alum saps the heat out of the combustion chamber faster than iron , heat is POWER , I assume you could put a coating on the alum head to slow the heat absorption ?

Posted By: PS Arrow

Re: steel vs aluminum heads. is steel better? - 07/01/09 02:21 PM

I would think the positive aspect is the weight savings, heat dissipation, and repair ability

Posted By: patrick

Re: steel vs aluminum heads. is steel better? - 07/01/09 04:35 PM

in theory both identical, the CAST IRON (nobody makes cast steel heads) would make more power due to slower head dissipation.

that said, one of the performance mags tested the theory on a SBC using some dart or AFR heads that ARE identical except for material, and guess what....they essentially made the same power.

I'd go aluminum for the weight savings/repairability aspect, unless the iron was significantly cheaper.

kinda moot though, as the only heads I know of that are essentially identical except for material are the indy S/R's that can be had in either iron or aluminum....

you can run more compression on aluminum heads becasue the higher heat dissipation helps reduce detonation.

Posted By: Cab_Burge

Re: steel vs aluminum heads. is steel better? - 07/01/09 04:38 PM

The iron heads will make more power with all things being equal, just like the block. Aluminum expands eight times more than cast iron so the compression does goes down as the motor warms up, the heat loss from the aluminum is another contributing factor also to the totaal power loss

Posted By: BobR

Re: steel vs aluminum heads. is steel better? - 07/01/09 05:35 PM

Quote:

in theory both identical, the CAST IRON (nobody makes cast steel heads) would make more power due to slower head dissipation.

that said, one of the performance mags tested the theory on a SBC using some dart or AFR heads that ARE identical except for material, and guess what....they essentially made the same power.

I'd go aluminum for the weight savings/repairability aspect, unless the iron was significantly cheaper.

kinda moot though, as the only heads I know of that are essentially identical except for material are the indy S/R's that can be had in either iron or aluminum....

you can run more compression on aluminum heads becasue the higher heat dissipation helps reduce detonation.

Patrick is right on with his post. I read the same article and if anything the aluminum made 1 or 2 more ponies. I, personally, think that aluminum is less prone to hotspots that could affect CC burn and therefore better. The theory is one thing but in practice the theory is irrelevant.

Posted By: BobR

Re: steel vs aluminum heads. is steel better? - 07/01/09 05:38 PM

Quote:

The iron heads will make more power with all things being equal, just like the block. Aluminum expands eight times more than cast iron so the compression does goes down as the motor warms up, the heat loss from the aluminum is another contributing factor also to the totaal power loss

We've found that the cylinders moving around in an aluminum block affecting ring seal to be much more rellevant than heat loss. Filling an aluminum block solves some of this.

Posted By: JohnRR

Re: steel vs aluminum heads. is steel better? - 07/01/09 06:05 PM

Quote:

kinda moot though, as the only heads I know of that are essentially identical except for material are the indy S/R's that can be had in either iron or aluminum....

I think it's only the 440-1 indy makes in alum and Iron .

Posted By: dirt

Re: steel vs aluminum heads. is steel better? - 07/01/09 06:55 PM

I will tell you where i am going with this. i have 2 motors apart now from 2 of my cars. one is a 340 the other is a 360.
I want the better running one to go in my 70 dart and the other in the car i drive more regularly.
the 340 has 10.5-1 forged pistons, with the eddy aluminum rpm heads it comes to 10.3-1 , not sure what it would be exactly with the factory j heads but it should be close to the same.
the 360 has hypertecnic pistons and a cast crank. with factory heads it should be around 8.8-1, with the edy rpm heads it should be around 9.3-1.
so i was thinking the 340 should run better than the 360. i still need to chose a cam yet . but the iron heads on the 340 almost make the compression to high for pump gas. that and i wonder how much good the heads would do on the lower compression 360 anyway. I thought that the 360 would run fine on pump gas with the iron heads but not the 340. in my head it would seem that the eddy heads would be better off on the 340 with a good cam. but what do you think?

Posted By: polyspheric

Re: steel vs aluminum heads. is steel better? - 07/01/09 07:23 PM

aluminum is less prone to hotspots

Yup - aluminum heat transfer by conduction is excellent, so local hot spots (plug, exhaust seat) dump heat to the surrounding casting very quickly.

Posted By: patrick

Re: steel vs aluminum heads. is steel better? - 07/01/09 07:29 PM

Quote:

Quote:

kinda moot though, as the only heads I know of that are essentially identical except for material are the indy S/R's that can be had in either iron or aluminum....

I think it's only the 440-1 indy makes in alum and Iron .

oh. I thought S/R's used to be available in iron....

Posted By: patrick

Re: steel vs aluminum heads. is steel better? - 07/01/09 07:55 PM

Quote:

I will tell you where i am going with this. i have 2 motors apart now from 2 of my cars. one is a 340 the other is a 360.
I want the better running one to go in my 70 dart and the other in the car i drive more regularly.
the 340 has 10.5-1 forged pistons, with the eddy aluminum rpm heads it comes to 10.3-1 , not sure what it would be exactly with the factory j heads but it should be close to the same.
the 360 has hypertecnic pistons and a cast crank. with factory heads it should be around 8.8-1, with the edy rpm heads it should be around 9.3-1.
so i was thinking the 340 should run better than the 360. i still need to chose a cam yet . but the iron heads on the 340 almost make the compression to high for pump gas. that and i wonder how much good the heads would do on the lower compression 360 anyway. I thought that the 360 would run fine on pump gas with the iron heads but not the 340. in my head it would seem that the eddy heads would be better off on the 340 with a good cam. but what do you think?

uncut J heads are going to be ~72cc, eddie's are (IIRC) 63 or 65, so either way, you're going to see about a 1/2 point+ difference, whether it's on the 340 or 360.

but we're talking apples to kumquats here, as the flow and (more importantly) combustion chamber isn't even close to the same (OOTB eddies flow in the 230-245 cfm range ootb, 1.88" valve J heads, in the 195-220 range, depending on who's bench)

whether or not it's too much compression is very dependent on camshaft choice, and most importantly, intake closing point. big cam with late intake closing point will lower your dynamic compression ratio, making high compression livable on pump gas.

quench also helps....some guys here report running KB107's at 0 deck and magnum heads and .040 gaskets(~10.6:1 static compression) and a comp XE268 and can run 89 octane w/o detonation. if you just swap to open chambered 340/360 heads, even though the compression might drop to closer to 10:1, you may have a hard time getting it to run on 92 octane due to lack of quench.

another thing in this compression ratio range, with no other changes, 1 point of static compression increase will yield 3-4% more power

say, you have a 300 HP/tq motor and raise the compression ratio by a point by milling the heads, no other changes. it'll probably make 309-312 HP/tq

now, HP/torque is also relatively linearly dependent on displacement. build a 340 and 360 identically (same heads, cam, compression, etc), the only difference being the 20 CID. the 360 is ~6% bigger, so it should make approximately 6% more torque, and probably ~6% more HP, unless the induction system is maxed out for smaller engine, in which case, the larger motor will make about the same HP, but at a lower RPM.

all told, the 360 being bigger, but lower compression to the 340, but with the same heads/cam/intake/exhaust, they'll probably be within spitting distance of each other, the 360 might actually still make a few more ponies & torque due to the increased displacement.

Posted By: 360view

Re: steel vs aluminum heads. is steel better? - 07/07/09 05:29 PM

here's a link to previous discussion of this subject, except that I was (and still am) more interested if there is an efficiency loss when using aluminum heads:

https://board.moparts.org/ubbthreads/show...rue#Post2782669

in a nutshell,
what I found was that there does not seem to be an efficiency hit from using aluminum cylinder heads with their higher thermal conductivity, despite what you may commonly hear.

the best article from that previous discussion was:
-------
Car Craft magazine has put this technical article up
on the subject of Aluminum versus Iron cylinder heads:

http://www.carcraft.com/techarticles/ccrp_0602_iron_versus_aluminum_cylinder_heads_test/index.html

sample quote:

"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."

Posted By: BobR

Re: steel vs aluminum heads. is steel better? - 07/07/09 08:37 PM

Quote:

here's a link to previous discussion of this subject, except that I was (and still am) more interested if there is an efficiency loss when using aluminum heads:

https://board.moparts.org/ubbthreads/show...rue#Post2782669

in a nutshell,
what I found was that there does not seem to be an efficiency hit from using aluminum cylinder heads with their higher thermal conductivity, despite what you may commonly hear.

the best article from that previous discussion was:
-------
Car Craft magazine has put this technical article up
on the subject of Aluminum versus Iron cylinder heads:

http://www.carcraft.com/techarticles/ccrp_0602_iron_versus_aluminum_cylinder_heads_test/index.html

sample quote:

"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."

Of course you realize that there will still be a number of people who will not accept this? Theory and real world actuality don't always align.