When Pontiac put the L98 into the T/A the first couple of years, I know GM wasn't too keen on it rivaling the power of the corvette in a mere Trans-am. But in 1990 to 1991, the L98 was rated @ 240-245 hp (depends on the source) and 340-345 ft-lb of torque vs the '89 figure of 235 (some sources say 225 for single cat cars) hp and 330 lb-ft of torque. My GTA is an '89 and it has the dual cat setup. If I remember right, some VIN check i ran recently told me that the car was manufactured late in the '89 model year. Plus the window sticker mentions the dual cats and with the literature I have looked at from that year I am assuming that it was originally rated at 235 hp and 330 lb-ft of torque (sorry for the exessive rambling ).

Anyway, I am curious to know what the differences are b/t '89 and '91 that gave those birds 10 mor ponies and 15 ft-lb of torque. Since I am tinkering with the MAF and some other parts trying to figure out what is what, I was wondering how much it would cost to make those changes and get the car up to '91 spec levels and if ya'll think it is worth it. Now I know there are other changes I could make that would be similar in cost, but may keep my car off the road for a few weeks. I basically want this car to be running fairly well and be a daily driver for about 6 months while I work on my Jeep. Once Jeep is finished then I will get into gutting the GTA and putting on some go fast goodies.

So, is it worth it to get some '91 stuff and swap out or no?

Thanks.

 

Well what ive been hearing is that in 87-89 the L98s were Mass Air flow aka MAF. In 1990 GM brought out the Speed Densitys which was on the L98s 1990-1992. (correct me if im wrong)I herd that they put lighter pistons as well and some other lil things. Now the Firebirds were rated less hp then the Camaro was, due to the intake design. Honestly if your willin to spend money on your car then i wouldnt go for a 1991 design. I herd that MAF is much better for modification then the Speed Densitys. So imho i think you should build you car up with mods and dont worry about the later L98s. yeah the 1990-1992 L98s were lil bit faster then the early ones, but i wont sweat it by makin it a 91 L98. Just mod it

also i herd they have changed the cam over the years

 

I agree with the above post. I also have a 1989 GTA with the dual cats and your numbers are correct with the 235HP. In 1990 GM went to speed density and that is why the extra couple of horse power. It has a slightly better intake system.

You intake system can be modified to be better yet. So like the above post said I would not worry about it if you are going for mods. I just finished having major mods done to mine and I'm now in the process of breaking in the new motor.

When I'm done with the break in process it will go on the dyno and get its final tune. Looking for around 400HP at the flywheel. Then on to the track. Allen

 

Does it matter what year you go w/ if you want to swap in a TPI system, but need to pass emissions? I'm goin' w/ the SDPC TPI Crate, but I need the wiring, etc. from a TPI car...but I heard, you can only swap engines/parts from the same year or newer to pass emissions...any word on that? I might just go w/ SuperRam, but I need to know if the younger years matter for parts. I have a '90 mpfi system now.