I've got a set of steel heads and also a set of 113 alum. corvette heads, both from 89 tpi's. just how much better are the alum. heads vs steel heads. i'm concerned about stripped spark plug and other holes, and header bolts backing out.

 

both will make the same power essentially, the alum can run slightly higher compression but that's about it. Figure 2% for that added 1 compression point

 

Didn't the vettes have higher flow numbers? I could have sworn I remembered reading this.

 

Yes, I've read it as well, pretty recently too. Will see if I can find the reference within the next few days...

 

Barely higher flow numbers, hardly enough to wiggle the needle on a dyno. Remember, the F-body and Corvette 350's both had the same camshaft and TPI intake manifold. The only difference was the heads, and the horsepower difference was either 5 or 10, depending on year.

 

And the HP difference had more to do with exhaust than the heads. The weight savings helps performance a little, but not power.

Either head needs some porting to get the most out of them. They also have intake mount bolt angle and cross-over passage differences (the aluminum not having the passages).

 

And thats pretty much negated by the additional heat loss of the aluminum.

 

It's a chicken/egg thing. Aluminum loses more heat, heat = energy, energy = power, so the compression is raised with aluminum heads to regain the lost power.

 

exactly my point, that unless the weight savings means anything to you there is no advantage.

 

I am putting the vette heads on my car so I can save 50lbs.
Aren't the vette heads 58cc while the iron L98 heads larger, which would mean you would get a little higher compression on an L98 when you put the vette heads on? I know on my 305 with 58cc iron heads that my compression will stay the same, so I don't get any boost in power in that area.

 

Exactly.

Well, you could say the iron L98 heads are 64cc and the '86-1/2-up Vette L98 aluminum heads are smaller, giving the aluminum headed engine the added compression needed to make up for the heat loss through the aluminum material.

Other than the weight savings, it's a zero-sum game.

 

I think the weight savings is the most important aspect, there's enough weight up front, dont need any more.

 

So would putting the alum 58cc vette heads on a 305 TPI result is less power than the stock 58cc iron heads?

 

There might be a slight benefit from the 1.94" intake valves, but with 1.94" intake valves in the stock iron heads, you'd get more power.

It's all about where & how you want to spend your upgrade money.

 

Suppsedly the aluminum L98 heads will only perform well once they're ported, stock ones are anything but impressive.
Here are the flow#'s https://www.thirdgen.org/forums/tbi/...-headflow.html

David Wizard writes in his book regarding porting/modifying Chevy heads, the aluminum L98 heads are ok if you can find them real dirt cheap or if you already have them, however one major issue is their low weight, due to their thin casting.

That's why they weigh in less than aftermarket aluminum heads, thin casting vs nice thick aftermarket casting.

Also, which ones are these, the "standard" exhaust port or the raised one ?

 

I'm pretty sure the intake flow #s will be identical, but I swear I've seen comparisons where the 113s outflow the iron heads on the exhaust side by 15cfm or so because of the raised ports.