I have just rebuilt the engine out of my 91 GTA and need help with puchasing heads. The engine was bored .040 and has speed pro hyperpuretic pistons (flat-top with valve reliefs). The intake is the Lingenfelter High flow intake and Accel high flow runners. The engine also has the Lingenfelter cam installed.

My main question is combustion cylinder size. I have heard I should get 60cc heads and I have also head 62cc heads. I am going to buy aluminum heads and want to maximize HP using pump gas.

Any help you can provide would be much appreciated. I do not want to puchase heads that will not work.

Thanks!

 

Does anyone have any suggestions?

 

If you don't need emissions, I"d look into a set of Vortec heads. Dollar for dollar, they're the best "stock" head you can buy. If you need emissions, or even if you don't, look into the Dart "Iron Eagle" heads. They're relatively new from Dart, and they, like the Vortec's are in the 64cc range. For your motor, you want 64CC, not much less or you'll push your compression up. To run on pump gas without issues, you really don't want to run more than 9.5:1 compression though you might be able to get away with up to 9.7:1. Even so, you'll have to run the 93 Octane gas.

 

Thanks for the help! I was looking at the Vortecs but my intake is not drilled for it, so I guess I am going to look at the Dart heads.

64cc is about what I thought. However, I have heard some say that you can go 10.5:1 and still use pump gas.

 

You can pick up a decent Vortec Intake for about $200.00 or so.

With aluminum heads and a reverse cooling LS1 motor which sends the coolant to the heads first, yes, you probably could but on the older motors with the standard cooling I personally wouldn't run over 9.8:1 just to be safe.

 

What size intake and exhaust port do I need?

 

What?
LT1's were reverse flow cooling, not LS1's.
You can use more CR with aluminum heads, and with fuel injection. Iron heads and a carb mean 10:1 is the limit, other factors greatly change that.

What cam exactly do you have? I only know about the lingenfelter 219/219 cam IIRC, is that the one?

Was your block decked at all? zero decked, or decked xyz thousandths?
Need more info to give better advice here.

What RPM range do you want to run the car in? I'm guessing this is a street car, 1500-5500RPM type of range?

 

This is mostly going to be a fun street and maybe strip car. I want something that is very drivable but sound and feel like a car with some real power. The cam I have is the 211/219. The specs are below.

Engine Naturally Aspirated Turbo or Supercharger Part Number Duration @.050
Valve lift Rocker Centerline Price
L98, LT1, LT4 x 74211 211/219 .530/.560 1.6 112 $349.95

I do not believe the block was decked at all. I think they just verified that it was straight.

I would think 1500 - 5500 RPM would be sufficient.

 

I stand corrected. I was under the impression that the LT1's were basically the same as the first gen motors with a few changes and it was the LS1 that was reverse cooling.

 

Calculate your CR at the keith black calculator then. I think 64cc would work ok for you, but you'll have crummy quench with a rebuilder gasket. Your call.

A 190ish cc intake port sized head would work well. Get a post 1987 style, so it'll bolt up to your intake. Don't use vortecs, since you'd need an all new TPI based intake for that. AFR, Dart, Trick flow, etc. You're going to be spending $1000 when the smoke clears, you might as well spend the few extra bucks and get the great ones.

 

Thanks, I really appreciate the help!

What is a rebuilder gasket and what can I do to get the best quench possible?

 

A rebuilder gasket is yer basic .040" thick gasket. A shim gasket is only .015-.020" or so. A shim will keep the quench low. You'll have about .045" of deck height already, so the smaller the gasket you can get away with, the better. Check your deck for flatness, use a straight edge and feeler gauges.

 

A "rebulider" gasket is a thick composite used to seal when either the block or heads may not be completely flat.

Quench is a combination of how far down in the cylinder the piston is at TDC and the thickness of the head gasket. You want that total to be in the .035"-.040" range. If your pistons are .025" down in the hole, a .015" compressed thickness will put you right at .040". If the block has been decked so the pistons are right at the block surface, get a .040" compressed thickness gasket. If they are .045" in the hole, get the block decked - you'll have too much quench space and you'll have detonation problems.

I think you're being too conservative with your CR. Aluminum heads need about .5 more CR than iron heads, so 60-62cc chambers, along with .040" quench, should be right in the ballpark.