Just for comparison reasons I need to know
a) what is the stock compression ratio for a Speed Density L98? I heard anywhere from 9.3:1-9.7:1

b) what are the stock L98 cam specs? I have a new comp cam with these specs and want to know how much more radical I'm getting.
Lift @.050- .500 intake .510 Exhaust
duration- 210 intake 220 exhaust
lobe seperation- 114
This cam is recommended for my blower setup and is good to 5800rpm.

I need these numbers to plug into DD2000 too so I can get some comparisons. Thanks!

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L98 w/ ATI ProCharger P600B 9psi, 2 core intercooler. (New L98 coming soon)
Pro-Built Stage 3 700-R4 w/ Continental 2400 stall TC
C5 wheels and tires.

92 Firebird Convertible- L03, 700-R4
Bone Stock
Me, my car and I
"Speed kills but it makes me feel alive" - White Zombie
Crazy street-racing idiot member of the All-Powerful Nor-Cal crew.

 

I've heard on here the speed density L98's got a bump in compression to 9.7:1 or so. The cam specs are in the cam tech article on here. Its 203/207, .413"/.428", 114 LSA, or so...

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West Coast GM Shootout 2001!
1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

 

Here is the specs I have for 1991's
4.9L (VIN B) 9.5:1
5.0L (VIN E & F) 9.3:1
5.7L (VIN 7) 9.8:1
5.7L (VIN 8) 10.25:1
Darrell
1991 GTA L98
Canada

 

I think thhe VIN 8 number you just quoted are for the Corteve with 58cc heads if I'm not mistakes. I think Kevins numbers are what I'm looking for.

 

9.8:1 sounds pretty high with cast iron heads for a factory setting, I never knew it was that high. Does GM require 92 octane for the 90-92 TPI F-bodies???
Does anyone know what the piston deck height was set at on these motors? Also the compressed head gasket thickness? Trying to figure what the stock "quench" height was.

Thanks

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Dave Zelinka

 

According to my 1991 GM shop manual for Firebirds, the L98 had 9.75:1 with 64cc heads. And yes, the manual recommends premium fuel. Oh, and all L98s have a VIN #8 in the 8th digit. There is no "7" to my knowledge.

 

GM has stated 92 octane or better in all its performance engines for as long as I remember. So of course its 92 octane for the 90-92 L98's, and 87-89 L98's, and 85-92 LB9's, too.