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SedanMan 03-08-2006 10:24 PM

Replacement heads for GM engines
I'm not sure how I can keep this thread from getting out of hand because it has potential to evoke passionate responses from both Ford and GM owners. However, it MUST be addressed and I thought by posting the question here that hopefully all/most/some of us could agree on what's fair. That said, here goes.....

I'm finalizing a letter to the CRB that will request alternate engine block and head castings for GM engines that are still in production. In order to finally have a GM bore/stroke equivalent to the Ford bore/stroke I'm suggesting a de-stroked 350 block that combined with a 3" stroke will yield the same 302 cu in displacement as the Fords. So far, so good.

The question then becomes what is the appropriate GM head (or heads) to mate with the 350 block? Even if you could still find the (2) currently legal GM castings, which are next to impossible to find, they wouldn't work with the larger bore of the 350 block.

The intent of this post is to get head recommendations that are fair from a performance standpoint and yet are readily available. We could debate this for days if not weeks/months/years, but I'm going to make a recommendation soon with or without a group consensus here. I'd just like to get advice from both Ford and GM people so we can suggest the best head(s).

I suppose flow bench numbers could be considered but often there's much more to the performance of a head than what you can measure on a bench. Runner shape, texture, swirl, valve shrouding, port matching, runner size, port volume......all contribute to combustion, not just flow. But even if we make this a huge research project I feel any suggestion will still be a best guess subject to scrutiny on the track. There is no 100% answer and compromise will probably be the name of the game.

So, let the suggestions begin. :)

jkopp 03-08-2006 11:24 PM

Bill, here are my 3 votes in order of preference (with notes accordingly):

#1 - "Double Hump" - GM P/N 88958692 - 2.02"I, 1.60"E Valves - 157cc Int Ports - Straight Plugs - Good old "double hump" heads - IMO, closest to the GT40/GT40P in flow and performance. The lowest performing head currently available from GM that will work on a 350 block.

#2 - L98 Corvette - GM P/N 12556463 - 1.94"I, 1.50"E, Valves - 163cc Int Ports - Angle Plugs - Corvette L98 heads - IMO, no freakin' way the Ford guys or the SCCA are going to let us use an aluminum head. This heads is not much better if not less of a performing head as the "double hump" head mentioned above. Besides, IMO, for the money, it is not worth it.

#3 - Vortec head - GM P/N 12558060 - 1.94"I, 1.50"E Valves - 170cc Int Ports - Straight Plugs - I firmly believe that although this cylinder head is cheap and readily available, it is too much of a performance increase to maintain equal parity between the GM and Ford powerplants. Although I will agree that the currently legal Ford head is the principal reason for disparity in the currently legal AS powerplants, I do not believe the Vortec head is the answer. This cylinder head WILL make more horsepower than either of the above mentioned heads and is, IMO, not the answer.

#4 - Sister 350 cylinder head to currently legal GM head - Although I do not have much technical info on this head, it is my understanding that it is virtually identical to the currently legal GM heads with the proper combustion chamber size for the bore of the 350 block. The downside is that, like the 305 casting, this cylinder head is no longer available from GM.

These are my opinions. YMMV. I'm going to get another beer...


SedanMan 03-09-2006 03:52 AM

the swinging pendulum
Thanks Jeff. Man, if you're going to get another beer then I'd say those are some pretty good late night, beer drinking suggestions!

I realize that we only have so many heads to choose from and although I'm all about fairness between the Fords and the GMs I'll bet that the Ford folks haven't lost too much sleep in the last number of years with their head advantage. So IF it turns out that a GM head ends up having a slight advantage then maybe it's time that the pendulum swings the other way for a few years and the GM guys shouldn't lose sleep over it either. Fair is fair.

Btw, do you have casting numbers for these heads?

jkopp 03-09-2006 12:08 PM


Originally Posted by SedanMan
Thanks Jeff. Man, if you're going to get another beer then I'd say those are some pretty good late night, beer drinking suggestions!

What can I say... I'm a professional (at the beer that is) .


Btw, do you have casting numbers for these heads?
P/N 88958692 = casting 3991492
P/N 12556463 = casting 10088113
P/N 12558060 = casting 10239906 or 12558062
Last head mentioned = P/N 10159552 = casting 14101083 or 14096217


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