I have a 400 sbc that ive been told was rebuilt, the compression is low with 72cc heads, I have vortec heads for it though. The same set up went 12.1 in a 7x camaro at 37xx pounds. So no doubt with the exzact set up, carb mods, suspension, I will be in the 11's. my only problem is, I want to spray the crap out of the motor, I have 2 years till i get my liscence I want the car to run now, BUT I really want to do everything right the first time. Whats the most compression ratio a street motor should have? CAR WILL NOT BE MY DAILY DRIVER! what else will i need to get to just upgrade pistons? How much does it run to have a shop do it? what will they exzactly do? Should I just get the rest of the parts i need to get the car runing and swap the motor in, and spray a low shot, or not at all?

 

Ill assume those are the cast iron vortecs....?

Which cam will you be running?


The ammount of compression you can get away with will depend on your cam and how much cylinder pressure it will bleed off.

Typically you will want to keep the static compression around the mid 9:1's and can get away with a few more points on an aluminum head.

On my little beater motor i came out to just over 10:1 static, but the cam brought my dynamic compression down low enough i could still run pump.

 

12 second car, and spray, and you're not even 16? You're not going to live to blow out the 20 candles on your cake at that rate....

I think he's going to use the big summit cam, 234/244

9.5:1 is where I'd be shooting for that big cam. Any higher and it'd be trickier to tune, you're not losing much by being as low as 9.5:1

I'd forget about the spray for now, you'll be sinking all your cash into keeping (or getting) it running NA, trust me on that one.

Run the math with different pistons and see which ones you want to use to get that CR. Probably a decent dish size on a 400cid with wee little 64cc heads

If the motor is rebuilt, what's in it now? Figure out the dish size on the current pistons, and piston depth, and run the math on that, see if it's where you want to be.