Do different year L03's have different ratios?

In the post below somebody's 92's owner's manual says 9.3 to 1, my '89 says 9.5 to 1.
https://www.thirdgen.org/messgboard/...ML/001003.html

Are the ratio's actually different or did GM just decide to change the "offical" number, like engine hp/torque numbers sometimes get played with?

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1989 Pontiac Firebird Formula LO3 Auto
-180 degree stat
-Hooker Cat-Back
-vinyl security shade, velcro t-top bag
*****Possible summer '01 mods*****
Dual Snorkle, Auburn Posi, Keyless Entry, Wonder Bar from my IROC, 4th gen seats, T/A tail lights

http://www.geocities.com/krt80/

 

yes, they are diff......no, GM wasn't B.S.ing...but if you were to test now.......things would be way diff obviously b/c of age of the engine

 

So which years got which ratio? What is different in the engines? the combustion chamber size? The piston shape? The head gaskets?

 

My 91 LO3 shows 9.3:1 in the manual. If there is in fact a 9.5:1 LO3, what would account for this difference in 89?

 

I'm not sure which years got which compression BUT I know the older L03's and LG4's got the 9.5 to 1 and the 91,92 got the 9.3 to 1 ratios. Well, it's well known that a change in head gasket thickness can raise or lower comperssion by .2 pts.....and I believe that's exactly what happenned for possible emissions factors that GM ran into.

 

so by changing gaskets on a 92, would you gain any performance if you boosted compression to 9.5:1

My guess would be not really, but just wondering what others think about it.

 

You'd probably gain a little, would'nt even be able to measure the gain probably.

 

I don't think you'll feel unless you REALLY know your car...... it might show up in better throttle response>>>Hard to tell though