I would like to know if there is any difference between the 5.7 liter, (350 cu. in.) Tuned Port Injected, V8 engine in the 1990 Trans Am GTA,...and the 5.7 liter V8 engine that is in the 1991 Trans Am GTA?

Thanks in advance!

 

If I recall correctly 90 was the last year for mass air flow, so the 91 would have been a speed density setup instead of maf.

 

1989 was the last year for maf. If anything a compression increase. The later l98's have flattop pistons. I know the 1989's have a dish to the pistons. Not sure when the flattop piston first occured. Maybe 1990 but 1991 for sure.

 

No difference what so ever between 1990, 1991, or 1992 engines. 1989 was the last year for MAF and dished pistons. '90-92's have flat top pistons.

 

On the L98s, the 1991 & 1992s are definitely 9.75:1 in compression and dual cats were standard. I was under the impression that 1990s were 9.50:1 and dual cats were optional. The slight increase in compression ratio between 1990 & the later were due to a thinner shim gasket used based on some discussion I had years ago with someone in GM Canada when I was trying to resolve the 240 vs 245 HP for the 1991/92 Firebirds.

For Import requirements into Canada, the 1990 Firebird L98s were rated 240 HP while the 1991/92s were rated 245 HP on their Import Declarations from GM. But, in all honesty, 5 HP is quite trivial - similar to the argument of which F-body is the most aerodynamic (and has the fastest top speed).