compression?

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Feb 26, 2009 | 03:12 AM

kaislick

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From: tulsa ok

compression?

I'm building a '95 LT-1, it's now a 383 stroker and I'm going the supercharger puts out about 8 lbs of boost. What is the max compression I can run on this motor? Does anyone know the ratio of cc's removed from the combustion chamber = what compression reduction? Any help appreciated, I've spent my time on a NA C6 the past year and now its time to beef up the C4!

Feb 26, 2009 | 10:33 AM

mn_vette

Melting Slicks

Joined: Jan 2002

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From: Jackson MI

Are you only going to be running 8psi on the 383ci? If you lower the CR you can run much more boost and have more HP overall. If you are planning on sticking to 8psi then 10:1 would be ok. For more than that I would go around 9:1.

What kind of pistons/crank and heads do you have? Chances are its going to be either new pistons or new heads if you want to lower the CR.

Feb 27, 2009 | 04:48 AM

Snakecharmer383

Melting Slicks

Joined: May 2004

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From: Earth

For a short time I ran 6-8 boost with 10.7 cr then I melted the head between 3-5 cylinders.

Mar 8, 2009 | 07:28 AM

"swamp rat"

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Quote:

Originally Posted by Snakecharmer383

For a short time I ran 6-8 boost with 10.7 cr then I melted the head between 3-5 cylinders.

Too much cr, you don't want to go over 9:1 9:5 Max!!! There are some out there running 9:1 with 12lbs. of boost !! Makin 650 RWHP! with a 350ci !!! I'M building a new engine a 355 ci with 9:1 cr I run nitrous & that works the same as a blower! you can get more out of It without a melt down!!!!

Mar 8, 2009 | 04:54 PM

BrianCunningham

Team Owner

Joined: Mar 2001

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From: Boston, Dallas, Detroit, SoCal, back to Boston MA

Decided to keep my compression @ 9:1 in case I want to pump my S-trim up to a T-trim.

Mar 8, 2009 | 11:13 PM

AKS Racing

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From: Houston TX

As I have said many times in prior posts, on a SC'ed street driven application, you want to keep the compression around 9.5:1+ SCR (even 10:1 is OK) or you wind up with a fairly "lazy" combo below 3000RPM. And we must all remember that for street cars (that are driven many miles in stop in go traffic) 3000RPM and below is where these cars will spend 95% of their life.

Now if it was for a weekend warrior, then I am in full support of lowering the compression further and raising the boost considerably.

Bottom line: 8 psi should be fine with 9.5:1+ SCR with a decent tune.
Aaron

Mar 9, 2009 | 07:49 AM

larry00

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From: D / FW

I can testify that my 383 w/9.8.1 CR and 8 lb.s blew both head gaskets at 6800 rpms on the dyno.
I decreased RPM's to 6200 and now I'm either going to put supercharger back on or replace JE dished blower pistons and put in a milder cam.
It ran great at 6200 but I sold the Procharger [ a mistake ]
I figure a couple of grand to reconfigure the engine without the blower.
So I guess I'm looking again for a blower and will stay with 6200 or lower !
Anybody got a P 1SC laying around they want to get rid of ?
Got Cash ! LOL

Last edited by larry00; Mar 9, 2009 at 07:58 AM.

Mar 9, 2009 | 06:32 PM

"swamp rat"

Instructor

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Quote:

Originally Posted by larry00

Get in line larry!!!

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Mar 9, 2009 | 09:40 PM

larry00

Race Director

Joined: Aug 2006

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From: D / FW

Quote:

Originally Posted by "swamp rat"

Get in line larry!!!

E Bay kit $ 4995 guess I will buy new ! D upgrade another $ 400.00
I can deal with that too .
going right now to check out the D upgrade at Procharger.

Mar 9, 2009 | 11:16 PM

#10

AKS Racing

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From: Houston TX

Quote:

Originally Posted by larry00

Why were you spinning the 383 to 6800? Hellacious cam, huge heads? Was power still increasing significantly above 6200?

I do not believe that the 9.8:1 SCR was the cause of the blown head gaskets at 6800RPM at 8 psi. 8 psi is 8 psi whether at 6200 or 6800 (or 4800). IMHO, there must have been other contributing factors to the failed head gasket.

I still firmly stand behind the 9.5 - 10.0 SCR recomendations for lower boost settings, provided the tune is up to par.
Aaron

BTW, skip the P1SC and go for the engine oil cooled D1

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