Which heads are better for overall performance?

L98 corvette aluminum heads

L31 vortec style, cast iron

 

The L31 Vortec head will outpower the L98 head no question. It's 10 times more efficient and has eliminate a bunch of restrictions found in previous head designs (ie L98). The more efficient you can be, the more power you can make.

 

The Vortec heads will outflow the L98's.

I got aluminum L98 heads because my stock compression is 8.3:1. So it's the flow AND the compression I was after. If I did my math right I should have 10.1:1 comp after the new heads. I also got a real good deal on them.

 

V8 Astro,
How do you like the GMPP 196/206 cam? That's the HT383 cam if I'm not mistaken. I'm gonna put one into a 305 and been looking for someone who's installed one into anything to get their impression of it.

 

I took my shortblock and heads into the machine shop yesterday, I'm building up a Vortec 355 for a buddy to put in his S10. The shop owner knew immediatly they were vortecs (chamber shape gives it away easily) and didn't have enough to say about them.
He told me a coupe times, I'm going to have a real healthy motor when I'm done "well over 300hp" he said a few times. And he told me the vortecs have a smaller chamber than they advertise, even with my dished low comp pistons of mine, he figures I will be close to 10:1
10:1 is about the highest I ever want to go on a street engine.

my 9.6:1 in my current vortec 350 (dish pistons also) has enough trouble with our crappy gas as it is.

 

Yeah most you will find measure around 61-62cc.

 

port out the l98's and you will have heads that rival the vortecs...but stock to stock the vortecs hands down

 

Agree. I've seen articles comparing various heads and generally "stock for stock" the Vortec head beats the Aluminum L98 heads for flow.

However, as mentioned by someone else the Aluminum L98 heads are easily ported and can give impressive flow numbers when done right. Polish the combusiton chambers and they will allow you to run some good spark advance curves. They do give a little weight savings which are also nice.

I don't know if the Vortecs are "angled heads", but the Aluminum L98 heads are. This can be either a disadvantage or an advantage. I find the angled heads of the Aluminum L98s make it a lot easier to access the spark plugs with my headers. Much easier than the "straight plug" Iron Heads.

One problem to be aware of with Aluminum heads, is they need to have bolts re-torqued all the time. I installed my a couple of weeks ago and I am re-torquing the intake and exhaust manifolds a third time. Hopefully, they will settle down, but I have also heard that you do have to "check the bolts" from time to time. You don't have to do this with cast iron.

If you want "maintainence free/minimal maintainence", go with cast iron. A lot of guys forget about the "tinker factor" of aluminum. I did.

 

There's a few adavantages that the L31 heads over the L98 heads that are already worked in.

The intake runners on the L98's use the dated pattern that has pushrod clearances that hamper performance. With the L31, it's been raised slightly and relocated nearly eliminating the pushrod clearances which can credit the head to much of its power increases.

The exhaust ports on the L31 use a slightly different design with good curves to gain efficieny on the exhaust side. The L98 (later designs, 88-91) use the D-port exhaust ports that can benefit from some porting, but still cannot really match the curves of the L31.

The combustion chambers are really key. The L98 uses a simple half moon chamber, while the L31 uses a kidney bean shaped chamber which increases quench. If you also see the chamber of the L31, it has somewhat of a pocket where the intake valve sits, which helps the intake charge. The exhaust valve in the L31 is significantly unshrouded which will help expel exhaust gases at any RPM. While they both have fast burn chambers, the L98's plug is aimed in the general direction of the exhaust valve, while the L31's has been placed almost right in the center of the chamber, and there's no question that the design will make tons of power.