L83/L98 head swap
 

New to the forum, I assume this questions's been covered before, but didn't get the info I ws looking for with a search.

Considering swapping my stock iron heads on the 84 L83 with L98 aluminum heads from a 1988 L98 I've got access to. 2 questions:

(1) Are the center bolt holes in the 88 heads compatible with the earlier 84 manifold? I know they switched at some point, but not sure when.

(2) Knowing the swap of 78cc to 58cc will raise compression to near 11:1 on my L83, does anyone have experience or knowlege of using thicker head gaskets to mitigate some of the compression rise?

Thanks, many more questions to come. BTW, If there is a specific forum more focused on the 82/84CFI, please let me know.

I'm referring to the intake manifold center bolt holes, sorry

not sure about the intake but arnt the 88 heads center bolt valve covers?

I believe the 86 aluminum heads have the same bolt pattern as your crossfire intake but the 87 and up heads had the different bolt pattern and center bolt valve covers. On my 84 I got rid of the factory 624 heads and bought some Summit cast iron 152123 large valve heads(made by Dart) for $630. They are 72 cc heads with .525 lift springs, screw in studs and modern fast burn angle plug design. Even with the aluminum heads you want to use the restrictive intake ports of the crossfire intake will impede any meaningful performance increase. I went with a carb conversion , a more agressive camshaft, true dual exhaust with no cat and the Summit heads and am very happy with the large power increase. Maybe you can get the whole 88 TPI set up along with the heads.

Most people do not realize that the iron 624 heads actually flow more than 113 heads. The weight savings might be worth half a tenth in the quarter. So not worth it. The 113's take to porting much easier (but expensive), if further mods are in the future. I am sure a few peeps have tried running 113's and flat top pistons, but it sounds like too much compression to me. Better off throwing some thin gaskets on the 624's.

The head gaskets on the 84 l83 are about as thin as you can get 015 steel shim

Im trying the renegade intake with the edelbrock performer heads. I really think you have to research all the things you want to do before you plunk down the bucks. The 113 heads and the 624 heads have the same intake manifold bolt pattern the center ones go straight in at the same angle as the outside ones

Thanks, appreciate the info. I have an x-ram purchased years ago and never used, and a spare CFI manifold avail for porting. Between those two options which will cost me nothing, and the renegade which I understand may be the best, but most expensive for me, I will need to make a chioce. My goals are not crazy. 300 hp woud be fine. The 88 heads I refer to are acutallly part of a complete L98 that I have, and may rebuild if it seems I can get what I want at a reasonable investment.

What are you doing with your throttle bodies if I may ask?

Yes, and if he goes this route, he needs to make sure that he doesn't use the typical replacement felpro, which is .039. Those Summit iron heads that Wilcar has on his, would be perfect for this build IMO. I believe member "Coupeguy" had some 113's on top of some flat top pistons, I believe he may have used 2 gaskets? It's been awhile.

The 624 thin cast heads are very prone to cracking on the exhaust valves near the heat crossover and most tech forums and Chevy high performance books state that the 624 heads are the worst of the worst heads to use and are not worth sinking any money into for a performance application. Maybe that is why I have not had one bite on my 624's for $99 on craigstist!!!!! One mechanic stated that out of 10 sets of 624's you might get one pair that is not cracked.

Are the 624's the same heads on the 85 L98's or are those different?

You should just use the entire L98 engine and put your X Ram or ported CFI intake on it.

The factory hyd roller cam is reason enough.
Will

That is new to me. Are the flow characteristics of these two heads documented? I had been under the impression from past reading that the alummnum D-port heads had better flow than the earlier iron corvette C4 heads, and that the 88 year heads were among the best. Thoughts?

1. Only on F-bodies and other models. On CORVETTES, the center intake bolts are still angled as they have been since '55.

2. No. It does work though. Check your push-rod length with the new gaskets.

its my understanding that the 113 heads do NOT flow much more than the old iron heads or even the old fuelie heads. They are better because of the swirl port chambers and intake port velocity, working the exhaust ports give good results on these heads. they are 22 pounds lighter...062 vortec heads are much better...said to be the best heads Chevy ever made .

I would seriously consider the GM Fast Burn heads. I just installed a set on my 91 and am very happy with them. The only problem I ran into with them is that they DO NOT accept center bolt valve covers. The shape of the gasket rail doesn't match up to the centerbolt pattern. You may also need to have your intake ports welded up to cover the taller port, but look carefull - the floor of the ports also had a mismatch.

Agree with you on the capability of vortec heads. But I am using either an X-ram or ported CFI manifold. Isn't there an intake port match issue in this case? I thought you had to have a vortec specific intake manifold.

eldlebrock produces a mainfold that mates the two generations.

Gary, the flow on all these heads is well documented. The 113's probably should not be used with flat top pistons w/ 58 CC chambers. 64 CC chambers would be as low as I would go on an aluminum head and 72 on anything iron. The exhaust is D port on the 113's, so you would need D port exhaust. You may be limited with your stock intake as to the size of intake ports on your heads. Many aftermarket aluminum heads have a 1206 size port, which your stock intake will not cover up. I am thinking maybe you could run a 1205 port, if you can port out a stock CFI manifold that far. Your intake is less than the size of a 1204 port. Edelbrock RPMs or E streets would be a good choice, but they are D port exhaust. A set of LT1 exhaust manifolds would fit these well. EDIT E Streets are square port, RPM's D port.

I had my throttle bodies bored by extreme efi I am really going slow on this rebuild/refresh but the throttle bodies seem to be done very nicely but I still need a few weeks to finish so I cant comment on how they work yet.Ive taken a few pics but I havent posted any yet.