Compression question

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Oct 26, 2003 | 02:06 PM

bohn333

Thread Starter

Junior Member

Joined: Aug 2003

Posts: 96

Likes: 0

From: Wisconsin

Car: 1987 Trans am

Engine: 350 TPI

Transmission: 700R4

Compression question

Whats the factory compression of a 89 5.7 IROC engine?
And what size combustion chamber do they have? Last and final question, what would the compression be with a stock L98 piston and 64cc vortex heads?

Oct 26, 2003 | 03:03 PM

8Mike9

Supreme Member

Joined: Jul 1999

Posts: 5,183

Likes: 42

From: Oakdale, Ca

Car: 89 IrocZ

Engine: L98-ish

Transmission: 700R4

The "book" says 9.3:1. Heads are spec'ed at 64cc.

Regardless of actual CR, if you put on a set of 64cc Vortecs, CR will remain the same.

Oct 27, 2003 | 03:33 AM

Quadrabog

Junior Member

Joined: Jun 2001

Posts: 16

Likes: 0

From: Millbury, Mass

Car: '86 Monte Carlo SS

Engine: L98

Transmission: T-56

What's the correct replacement piston to maintain 9.3:1 when using 64cc heads? Dished or flattop?
Summit #'s
STL-H345NP30 9.35:1 w/ 64cc heads. Flattop, looks like the one to use.
STL-H423NP30 8.90:1 w/ 64cc heads. Dished, engine builder swears this is the right piston.

Anyone?