Thread: Simple engine mod question

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Hello guys. I did some mods to my 81 Corvette, and it seems to run alot better, as I expected it would.
Originally it had a 350 w/computer controlled Q-jet and Dist. Pollution eqiupment, all stock. Has a 2.87 posi and single exhaust out the back duals.
27 inch tires and 7.8 cr, and a super small cam(stock) not sure of specs but I think about .390 lift.
Well, I don't like to waste tons of money, but I like to match parts as best I can.
I removed the smog stuff, and carb and dist. I installed a Regular Q-jet and a performer intake. I installed a new HEI w curve kit. I put headers on and TRUE duals out the back. It has a TH-350 trans, and now the rear gears are 3.73.
The cam I picked was comp Cams #12-231-2 which is 206/214 dur and 432/453 lift 111lc.
The car was a true dog before, but seems to get up and go (for what it is).
My question is now, If I were to get rid of the old 76 cc heads and upgrade to something like a Vortc or sportsman II or even an older casting with acc. bolt holes that are 64cc, would I notice much more of a difference, or it that a waste of cash. The issue with putting the heads on is no big deal to me, can do it in about 4 hours, but will I really get much more out of it with the cr being raise a little? Let me know. Thanks.

They say for every 1 point of compression you'll get 20 horsepower more. Changing your heads to 64cc will give you about 0.8 more compression. Along with a better combustion chamber and better flow, you'll notice a huge difference. The smog 76cc heads are the worst heads for making power.

The cam you're running now is out on the ragged edge of being too big for the 7.8:1 static compression ratio. 69elko is right on the money with the 0.8 compression ratio change when going to 64 cc heads. 7.81 to 8.69. Use the 12558060 L31 Vortecs if you want the best low-buck iron heads. They'll flow better than any other OEM Chevy head and probably better than most of the aftermarket iron heads. They're perfect for a 350 with flat-tops. You'll have to change the intake to a Vortec-specific manifold, use rail rockers and center-bolt valve covers. Keep the cam you have now. It's perfect for a 8.69 c.r. and your 0.453" valve lift should clear the stock valve seals.
Here's some blah-blah about the L31's....
Scroll halfway down and click on "GM L31 Vortec Heads"
http://www.gilbertchevy.com/frame.ht...ankshafts.html

get some 49cc darts if you have the clearence to run them. that will get you right around 9.5:1 I belive, and you could run a larger cam.

Originally Posted by Matt167

get some 49cc darts if you have the clearence to run them. that will get you right around 9.5:1 I belive, and you could run a larger cam.

49cc heads would put him at 10.17:1
The problem with that is that the stock Chevy pistons don't have a crown with enough flat area to achieve a good squish and you can't run over about 9:1 without a good squish. You'd have to go to aftermarket dished pistons with the dish offset to the chamber side of the piston to make it work right. Not only that, but there is way too much piston deck height in the stock arrangement even if the pistons were true flat-tops. You'd have to deck the be-jesus out of the block and if you're gonna do that, you may as well use the correct pistons in the first place.

Thank you for the quick answers. Let me ask this. Am I able to goto the salvage yard (guy I work with family owns a big yard in Philly.) and get these heads? If so, what did they come on? The reason I ask is that way I can get the rockers heads valve covers, ect and I will dissasemble everything and put them in our typhon machine and clean them all up. I can also do the head work(valve job)here. Let me know if you can figure out what chevys I should hunt for, if in fact you know. Thanks Guys.

Code L31, found in '96-up Vortec 5700 motors.
Here's how to look for 'em in a boneyard............
http://www.chevymania.com/tech/vortec.htm
Pull the valve covers and verify the casting numbers before layin' down your green.
Remember, the stock retainers/springs are only good for a theoretical valve lift of about 0.450" before the retainer slams into the stock seal. And by the way, the stock seals may not be fully seated on the boss. Use a socket to tap 'em down to be sure. If you're gonna go any higher on lift, replace the springs and retainers with the Crane Cams kit #10309-1 springs and retainers, good for 0.550" lift with no machining. Just drop 'em in using the stock seals.

With any bigger spring he would have to tap 'em for screwin studs also. Vortec's only come with pressed in, unless you buy them from Summit and then they have them ready for .525" lift for $750. Or you can buy them stock for $550 I believe. If you can get them used in good condition I'd do that and just put the extra work in them.