1FASASZ

im building a 383 and i want to run 11.5 to one compression. is that to much for the street?

mohawkmike

Generally speaking 11:1 is as much as you wanna squeeze on a premium pump gas motor (W/aluminum heads). I faced the same problem on my 355 LT-1 When I chopped the Decks down to zero and later found out I was gonna have too much compression. So I called cometic gasket co. and $200 later I had a set of .060 squish gaskets to fix my stupid mistake. I wouldn't try it unless you wanna burn race gas all the time.

97Z-M6

not a problem at all.

1racerdude

You have to consider the cam when you figure compression. The static compression don't mean s***. You need to figure your dynamic compression and this is dependent on your intake valve closing point. A 9.0/1 dynamic is the max for pump gas.
Do a search and get a program to figure your DCR. I am running 12.97 static compression on pump gas on the street and a good dyno tune.

96speed

I'm running ~12:1 static in mine, but I only run pump gas when its <70º ambient with low humidity. Just have to be smart about it.

Ryan

1racerdude

Yea and a spot on tune by someone who knows what they are doing.
What is your dynamic compression ratio?

1FASASZ

so you never have a problem with detonation or anything?

1FASASZ

before i blew my motor Lloyd told me my c/r would be around 11.3:1, alot of people have the same set up i do and dont seem to have a proplem. does the fact that my motor is gonna be a 383 change the c/r from a 350?

onebadponcho

^^^^^^
What he said.....and use this: http://www.rbracing-rsr.com/comprAdvHD.htm .....to figure it out. If I remember right, my setup has a 9.1 DCR.

1racerdude

Do you know what your timing is set at? Have you had any problems with rattling the motor?

onebadponcho

I don't know what the timing is set at. I'm sure MadZ knows; he tuned my PCM. I ran it on the stock tune for quite awhile though, and I've never had problems with detonation. I can remember doing my cam/heads; initially I was going to use the thinner Impala head gaskets, then calculated my DCR. That lead me to use the thicker Felpro head gaskets part#1074 (I believe), so I can remember being close to the edge of my DCR being too high.

fireman

I'm at 11.8:1 and I run 91 octane. I have heard it knock before when it was over 100* last summer. I probably just won't drive it at all this summer.

I would stay at 11:1 or lower if you plan to drive it year round.

1racerdude

Your DCR is probably more than 9.0.

1FASASZ

so should i just do 11.1 just to be safe. id rather do 11.5 if i can get away with it on 91 octain.

1racerdude

You need to figure your DCR and then see if it is less than 9.0 to one. Half the people on this board don't know what their's is.All they know is static. And it depends on YOUR set up and cam and not someone else's set up.