Vortec or AFR Heads?

[Shawn]

Well, again, it comes down to aluminum saving you weight.

If 9:1 on iron heads (fast burn chambers are going to let you run 87 at that compression easily) make as much power as 10:1 AL heads, there is no difference except that you have more compression.

But the AFR's are fast burn too. Just called them up and asked. Dave at AFR said it was from the heart shape design that determins if the head is fast burn or not.

He also suggested 190's over the 180's for a 400 SBC.

But still, all things being equal, wouldn't 10:1 give you more HP/TQ compared to 9:1 if both heads were fast burn?

http://www.chevyhiperformance.com/techarticles/148_0401_imp/index.html

After a few pulls, the AFR cylinder heads with 180cc intake runners made nearly the same amount of torque as the original configuration (Vortecs), but it did so 700 rpm higher in the power curve, adding 49 hp to the best Vortec dyno run. Remember, these gains came from a motor with less compression

Also, how did you get the TPI to fit your Vortec heads?

 

[dyeager535]

Again, that article points to an increase in RPM compared to Vortecs. Like we discussed, thats your low/topend tradeoff that is probably worth it.

10:1 on an iron head would make more power than 9:1, everything else being equal. Same holds true for AL, but at the same compression, the iron is making more power.

The same on an AL head would be true. BUT the iron makes more power at the same compression, so to even equal iron head performance in an AL head, you HAVE to run the extra point or so.

The problem you run into is that the iron heads won't tolerate the higher compression because the iron retains more heat, so you can't just bump up to 10:1 and expect to run 87, like you can with AL.

TPI fit my Vortec heads via a vortec specific intake sold by only two companies at this point, and cost enough money that I should have bought Torquers or AFR's off the bat. Then again, $250 or so for my Vortecs brand new, even with the additional money I had to dump into them, I'm still in them less than aftermarket heads. But injection and Vortecs is a whole different ballgame.

 

[ryan22re]

i think it has alot to do with the fact that alum heads dissapate heat better than cast iron. the heat generated from combustion ends up in the alum cylinder head vs keeping it in the combustion chamber with an iron head. thats why people raise the compression ratio when switching to alum heads. because they have to, to make similar power numbers. since gasoline engines convert 1/3 of the energy in fuel into heat, and alum dissapates the heat quicker, its easy to see where the power goes.

aside from the weight savings, the other good thing is that they are easier to port and polish. and repaired if you ever crack one.


ryan

 

[Shawn]

Again, that article points to an increase in RPM compared to Vortecs. Like we discussed, thats your low/topend tradeoff that is probably worth it.

10:1 on an iron head would make more power than 9:1, everything else being equal. Same holds true for AL, but at the same compression, the iron is making more power.

The same on an AL head would be true. BUT the iron makes more power at the same compression, so to even equal iron head performance in an AL head, you HAVE to run the extra point or so.

The problem you run into is that the iron heads won't tolerate the higher compression because the iron retains more heat, so you can't just bump up to 10:1 and expect to run 87, like you can with AL.

TPI fit my Vortec heads via a vortec specific intake sold by only two companies at this point, and cost enough money that I should have bought Torquers or AFR's off the bat. Then again, $250 or so for my Vortecs brand new, even with the additional money I had to dump into them, I'm still in them less than aftermarket heads. But injection and Vortecs is a whole different ballgame.

Thanks for the info Dorian! I was looking at TPI but it doesn't look that easy to install even with the aftermarket harness you can buy. I was going to buy that same manifold for the Vortecs. Still have to get a TPI chip burned to match your engine and purchase larger injectors. <sigh>

 

[ryan22re]

The problem you run into is that the iron heads won't tolerate the higher compression because the iron retains more heat, so you can't just bump up to 10:1 and expect to run 87, like you can with AL.

i disagree with that. the iron head LT1's in the caprice/roadmasters had 10.4:1 compression and a real boring cam. the L31 vortec motors have 9.7:1. the real difference is in the fuel and spark tuning.

ryan

 

[ryan22re]

I have heard before(who knows if its believable) that the people at AFR helped GM design the Vortec heads. AFR uses the same combustion chamber design as Vortec heads from what I've always been told.

the vortec heads are really just iron versions of the LT1 alum heads. with normal cooling jackets. afr may have worked with gm on the 92-97 LT1's but not the vortecs.

ryan

 

[Z3PR]

Don't forget about the Dart Pro 1 heads.

 

[sled_dog]

i disagree with that. the iron head LT1's in the caprice/roadmasters had 10.4:1 compression and a real boring cam. the L31 vortec motors have 9.7:1. the real difference is in the fuel and spark tuning.

ryan

and chamber design and piston design, and finish of the chamber, heck valves can play a part too... The "fastburn chamber" has a good bit to do with the tolerance for compression. My 97 Vortec runs like a champ on 87 octane.

 

[beater_k20]

the vortec heads are really just iron versions of the LT1 alum heads. with normal cooling jackets. afr may have worked with gm on the 92-97 LT1's but not the vortecs.

if AFR worked with GM on the LT1 heads, they also indirectly worked on the Vortec heads as well.

 

[Shawn]

i disagree with that. the iron head LT1's in the caprice/roadmasters had 10.4:1 compression and a real boring cam. the L31 vortec motors have 9.7:1. the real difference is in the fuel and spark tuning.

ryan

One of the greatest features of the '92 and up Chevrolet LT1 engine is the reverse flow cooling system. In fact it is reverse flow cooling that is truly the key to the incredible performance of the modern LT1. Reverse flow cooling is vastly superior to the conventional cooling systems used on virtually all other engines. This is because it cools the cylinder heads first, preventing detonation and allowing for a much higher compression ratio and more spark advance on a given grade of gasoline. A fringe benefit is that cylinder bore temperatures are higher and more uniform, which reduces piston ring friction. Because of this new cooling system, the LT1 can easily meet ever-increasing emissions standards with significant gains in power, durability, and reliability.

I didn't know the L31 had 9.7:1 compression. Hmmm...

 

[beater_k20]

I didn't know the L31 had 9.7:1 compression. Hmmm...

i've heard varying specs from 9.4-9.7:1, but have yet to actually run the numbers on my Vortec 5.7.

 

[ryan22re]

my bad, i got my head up my you know what. just checked gm service manual.

96-99 L31 has 9.4:1

we wont let .3 get between us will we?


ryan

 

[Shawn]

I just wanted to say thanks again for everyone's input on this!

 

[dyeager535]

and chamber design and piston design, and finish of the chamber, heck valves can play a part too... The "fastburn chamber" has a good bit to do with the tolerance for compression. My 97 Vortec runs like a champ on 87 octane.

Even the non-AL headed L98's ran pretty lame compression when compared to what Vortecs run, which is a fair enough comparison figuring injection system is similar.

It wouldn't be fair for me to say that the only reason older 87 octane tolerant SBC engines ran such low compression (as a whole) was because of combustion chamber design, while the fast burn chamber bumped that up almost a full point. (carburetion/TBI vs. port injection)

 

[beater_k20]

Even the non-AL headed L98's ran pretty lame compression when compared to what Vortecs run, which is a fair enough comparison figuring injection system is similar.

not a fair comparison at all, the flow numbers for both heads are very different. and im not sure that the L98s had a fast burn combustion chamber.

 

[sled_dog]

they didn't, that was the point. They didn't have the chambers, older EFI system, low compression to make them run on 87 octane.

VS Fastburns, better fuel injection and computer control + chamber design = more compression with same fuel.

 

[Diesel Dan]

Wow! Hot topic.
Just skimmed thru it and wanted to add a couple of things. Regarding the iron vortec heads, which castings were they using? There is the production L31 head(2 versions), most common. And recently GM performance has released two other iron vortec heads, one small and one large port. Basically the fast burn aluminum in a cast iron version. IIRC the valve size was 2.00/1.55.

On compression of the L31, yes it may be spec'ed at 9.4:1 but I wonder how close it really is. After tearing down a L31 it has dished pistons sitting .024-.029" below the deck . Now a '92 era L05 motor out of a Buick roadmaster with TBI had flattops in it, also with roller cam but TBI.

Did they test the Edelbrock Etec heads? The larger 200cc port heads are supposed to make ~20hp more than the GM fast burn aluminums.

 

[beater_k20]

Wow! Hot topic.
Just skimmed thru it and wanted to add a couple of things. Regarding the iron vortec heads, which castings were they using? There is the production L31 head(2 versions), most common. And recently GM performance has released two other iron vortec heads, one small and one large port. Basically the fast burn aluminum in a cast iron version. IIRC the valve size was 2.00/1.55.

while there are two different casting numbers for Vortec heads, one with a heavier valve seat (for heavier trucks), both flow pretty much identical. both casting numbers were used in production, and one of the production part numbers is marketed as the GMPP Vortec head. i hadnt previously seen the new Vortec heads before, your post got me curious, so i went looking. im very curious as to how the perform.

 

[theperfectgarage]

According to the late,great Mr. Lingenfelter, the heavier truck vortec casting does NOT flow like the lighter truck # and should be avoided. check into this before buying.

 

[beater_k20]

According to the late,great Mr. Lingenfelter, the heavier truck vortec casting does NOT flow like the lighter truck # and should be avoided. check into this before buying.

actually, that was printed in Chevy High Performance Magazine (and possibly other Primedia rags -ex: Hot Rod, Car Craft, etc) and was later retracted because it was found to be untrue.