Iron vs. Aluminum
01-17-2004, 04:50 PM
#1
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Iron vs. Aluminum
I'm just trying to cause trouble here 
And I quote again
.....hmmmmm, everyone read that again.......
Let's see.....$100 iron LQ4 heads that flow the same as $700 aluminum LQ4 heads.....tough choice there
Originally Posted by Chevy High Performance Magazine
One of the most frequently asked cylinder-head questions is, “Is aluminum that much better than iron?” CHP performed a test using a 383ci small-block with a Crane PowerMax roller cam (232/240 at 0.050 with 0.525/0.543-inch lift) fitted with a pair of almost-identical World Products Sportsman II iron and Sportsman II Lite aluminum heads. The heads offered almost identical port configurations and intake port volumes (200 cc), valve sizes, and chamber sizes. In fact, the only difference was that the aluminum heads used CNC-machined combustion chambers while the iron heads were as cast.
Accepted cylinder-head theory contends that iron heads do not conduct as much heat away from the cylinder as aluminum does, so the iron heads should make more power—everything else being equal. Surprisingly, in our test the aluminum heads made more power than the iron heads by an average of 4.6 hp throughout the entire curve. The iron heads made a peak of 407 hp and 449 lb-ft of torque, while the aluminum heads made 408 hp and 454 lb-ft of torque. We attributed the difference to the aluminum’s CNC-machined chamber, which improved combustion efficiency. We still believe that given true identical iron and aluminum heads, the difference would have been 1 or 2 percent in favor of the iron heads.
The more important question is not really iron versus aluminum, but rather the airflow potential of the heads in question relative to their price. Given this criterion, the best head would be the one with the most intake and exhaust airflow for the least amount of money. Aluminum weighs less and is generally much easier to repair. Iron is less expensive but weighs more. The choice is up to you.
Accepted cylinder-head theory contends that iron heads do not conduct as much heat away from the cylinder as aluminum does, so the iron heads should make more power—everything else being equal. Surprisingly, in our test the aluminum heads made more power than the iron heads by an average of 4.6 hp throughout the entire curve. The iron heads made a peak of 407 hp and 449 lb-ft of torque, while the aluminum heads made 408 hp and 454 lb-ft of torque. We attributed the difference to the aluminum’s CNC-machined chamber, which improved combustion efficiency. We still believe that given true identical iron and aluminum heads, the difference would have been 1 or 2 percent in favor of the iron heads.
The more important question is not really iron versus aluminum, but rather the airflow potential of the heads in question relative to their price. Given this criterion, the best head would be the one with the most intake and exhaust airflow for the least amount of money. Aluminum weighs less and is generally much easier to repair. Iron is less expensive but weighs more. The choice is up to you.
Originally Posted by Chevy High Performance Magazine
The more important question is not really iron versus aluminum, but rather the airflow potential of the heads in question relative to their price
Let's see.....$100 iron LQ4 heads that flow the same as $700 aluminum LQ4 heads.....tough choice there
01-17-2004, 07:25 PM
#3
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It is very good information and a good point for those looking to modify vehicles. However, the manufacturers are moving to aluminum to try and reduce vehicle mass. Soon, there will only be aluminum parts for a given genearation of engine(the new LS2 may be the first for GM, in fact, as I hear the new DOD truck blocks will be aluminum 4.8L - 6.0L) and there won't be this choice.
Todd
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01-18-2004, 12:20 AM
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Also, keep in mind, that motor was a carburated non-computer controlled motor. There is no such thing as knock sensors on that motor. Trust me on this one, an aluminum head motor will see LESS detonation than an iron head motor on pump gas. I'm sure you know what happens when the computer senses knock (detonation), it RETARDS the timing and HP goes down. Do what you want, its your deal. But my vote goes with everyone else's, Aluminum hands down. Flow isn't the only thing that we are talkin' here.
01-18-2004, 02:38 AM
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Originally Posted by BADMOFO
Also, keep in mind, that motor was a carburated non-computer controlled motor. There is no such thing as knock sensors on that motor. Trust me on this one, an aluminum head motor will see LESS detonation than an iron head motor on pump gas. I'm sure you know what happens when the computer senses knock (detonation), it RETARDS the timing and HP goes down. Do what you want, its your deal. But my vote goes with everyone else's, Aluminum hands down. Flow isn't the only thing that we are talkin' here.
Exactly, I agree 100%. If you run the exact same setup on the aluminum heads and iron heads, the iron will make more power, but once you start tuning it to make max power, the aluminum ones will make more because you will be able to run more timing before you start to ping. These motors ping pretty easily, and trying to run a performance setup on the iron heads will just make it that much worse
Also I agree with BigTex, i dont think they are identical runners
01-18-2004, 10:37 AM
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I've done a good bit of research on this and you guys have the right idea. If everything is identical with stock type tunes, the engines should produce identical torque and HP curves.
Now, If you want to tailor heads to enhance torque production through about 5,000 RPM's, iron is preferred because they retain combustion heat rather than dissipate it. That way, the heat energy from combustion can be translated into thrusting the piston down in the power stroke. The LQ4 iron heads can be hand ported, but CNC shops won't touch them because of the hardness of cast iron. It will dull their tools in short order. The iron heads weigh about 50 to 70 pounds more as I remember.
Alternately, the aluminum heads dissipate heat and can be tailored to enhance horsepower production in the upper RPM register (lets say 4,000 to 8,000 for these engines). Especially at higher compression ratios, pre-ignition (pinging) can be a problem which requires the timing to be retarded by the PCM. With aluminum, the heat is better dissipated and naturally reduces pinging allowing the PCM to keep the timing advanced. Additionally, aluminum lends itself to CNC machining with carbide tools.
Within another three to five years, I believe that all automotive engines (block and heads and I'm including light trucks here) will be aluminum. They reduce the vehicle mass and contribute to a better corporate average fleet economy (CAFE) which the manufacturers such as GM worry about to remain in compliance with the EPA requirements.
Now, If you want to tailor heads to enhance torque production through about 5,000 RPM's, iron is preferred because they retain combustion heat rather than dissipate it. That way, the heat energy from combustion can be translated into thrusting the piston down in the power stroke. The LQ4 iron heads can be hand ported, but CNC shops won't touch them because of the hardness of cast iron. It will dull their tools in short order. The iron heads weigh about 50 to 70 pounds more as I remember.
Alternately, the aluminum heads dissipate heat and can be tailored to enhance horsepower production in the upper RPM register (lets say 4,000 to 8,000 for these engines). Especially at higher compression ratios, pre-ignition (pinging) can be a problem which requires the timing to be retarded by the PCM. With aluminum, the heat is better dissipated and naturally reduces pinging allowing the PCM to keep the timing advanced. Additionally, aluminum lends itself to CNC machining with carbide tools.
Within another three to five years, I believe that all automotive engines (block and heads and I'm including light trucks here) will be aluminum. They reduce the vehicle mass and contribute to a better corporate average fleet economy (CAFE) which the manufacturers such as GM worry about to remain in compliance with the EPA requirements.
01-18-2004, 02:44 PM
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yelo, if you're seeing 700 for a set of 6.0 heads you're looking in all the wrong places. you can get them on ebay for 200-400 all day long. and you can get LS1 heads on there and this site for 150-300 depending on the seller. i bought a set of mildly ported 5.3 heads with stock valves and chambers for 150 bucks a while back...but that was a steal and a good deal. sold'em for my wet kit and made pretty much 400% profit outta the deal. just look a little more and you'll find some cheaper stock heads.
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01-18-2004, 03:25 PM
#8
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I think if I lived in Death Valley I'd go with the aluminum heads to dissapate engine heat and look into some Evans coolant to keep air pockets from captivating in the motor.As hot as it gets where you are I'd think you'd want every edge you could get.
01-18-2004, 04:07 PM
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