383 compression?
 

Hey guys i just bought a 383 kit , i have options going with flat tops or dished pistons, if i go with flat tops compression will be around 11:8:1 without decking or anyhting and if i go with dished compression will be 10:4:1.

11:8 isnt that to much for a daily drive/street car?

Or are there ways to lower the compression, i've heard you can tune it someways and u'll be fine .

Any options or just go with dished since it's easier to go up compression then go down.

thanx

-Chris

Re: 383 compression?
 

You need to say what cam you are using. Do a search for "dynamic compression ratio". It has been discussed several times. There was a thread recently dealing with exactly this subject. People might yell at you around here for not searching...

Re: 383 compression?
 

well, I had the same problem. I decided to use the dished pistons, and deck the block. I decked my block .015 cause thats about the max you can go w/o machining the angle on the intake to match th enew angle/height of the heads. and I used the impala head gaskets. Im around 11:1. you dont really have that much of a choice. the way I figured it, if you do the flat top piston, you CANT deck the heads or block even if you need to due to the high SCR. you would also have to run a thicker then stock head gasket. forget who (prolly felpro) but someone makes a head gasket that is .050" thick to help lower the SCR. or you could buy some aftermarket heads w/a 64 or 76cc combustion chamber. decisions decisions.
chris

Re: 383 compression?
 

11.8 is not going to be very good with ****ty gas nowadays although it could be done, i would go with the dished pistons, it would really help keep from pinging and causing timing retardation

Re: 383 compression?
 

What compression are you looking for? My SRP 16cc dished pistons with my head gaskets is at 10.7:1. I could have went with a thinner head gasket and been closer to 11:1 but wanted to stay near stock. Between milling and head gaskets, you have many combinations above and below the 11:1 ratio. How much over or below would depend on what you decide.

Re: 383 compression?
 

I would go with a 12-18cc dish it's alot easier to handle a street car with manageable compression than to worry about the state of tune continually.

If you have a freind or close by a person that can put a dead on tune then the higher compression can be OK, but as said the Flattops will not allow you to have the block decked if it needs it much past a clean-up.

Re: 383 compression?
 

12336-040 pistons

The 12336-040 piston is what I'm using with the LT4 54.4cc chamber. Gm847 cam and the Impala gasket. Been told it will be ok, but unsure, as it is not running.

Re: 383 compression?
 

thats quite a bit of compression, it says with a .010 deck surface that it is 12.0 (with .038 head gasket.) With a 54 cc chamber its about 12.5:1 !!!

I would go with this one from Probe..

http://probeindustries.com/Pistons/P...v_383_dish.htm

Use the part # 12345-030.

Re: 383 compression?
 

Well it will be 11:8 if i zero deck the block but i dont have to and im going to use a thicker gasket, i'll be around 10:9 - 11:1 . I got it worked out already thanx for your help guys .

-chris

Re: 383 compression?
 

I thought that was way to much as well, but the machine shop seems to think they are perfect. The long block is almost done now, or I would change those.

Re: 383 compression?
 

You could go with the factory head gasket and lower the compression by a half a point. The 847 will bleed quite a bit of compression of so I don't completely think it's unmanageable in a street car, I think you'll just need a good tune and good gas.

Re: 383 compression?
 

I've thought about using the stock gasket. My only concern is the chance of blowing it. I'm planning on using some nitrous, at least 200. I'll just keep my fingers crossed.

Re: 383 compression?
 

The Felpro is an excellent gasket and thicker than the impala gasket as well.

Re: 383 compression?
 

I'll try it out, thanks for the info. :thumb:

Re: 383 compression?
 

No problem, good luck with the build!!!

(let us know how it goes)