I've got a 89 Iroc Z, L98, 700r4. I've all ready got the maf descreened, trays cut out of the air box, K and Ns, Hedman shortys and Y pipe, No cat, and a flowmaster muffler. I'm about to put put a 28 spline carrier and 342 gear out of my 02 WS6 in it. I'm not sure of the gearing now but I know its lower because it originally had a 9 bolt and now has a 10. What should my next mod be? I've been thinking about a transgo shift kit and a air foil along with a external cooler but what after that?

I'd do a torque converter and suspension mods. Then maybe get into tuning. Perfect time to start with a mild bolt on factory car

Spend some big bux on a trans rebuild and good torque converter.

I agree with that. I have a simular set up to you in my car. A good trans rebuild with high stall converter will really wake your car up. Especially since you are going to get 3.42 gears. For long tube runner TPI style cars 3.42 is a good ratio for all around performance.

ive also got a simular set up as u do ive put the 342 gears air foil msd 6al hooker headers dual exhaust kn filters relocation brackets from founders performance there price is decent but like what was said the torque converter would be also my next mod

What would a good rebuild cost? What do I need to upgrade while its apart to handle some extra power. I eventually plan to rebuild the motor and do heads/cam/HSR. This car is my DD so it won't be anything to radical. I'd like to have a mid to high 12s car in the end.

call
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A good performance rebuild for say 450-500 hp would be 1000-1200 I'd expect. All depends tho

Besides the trans cooler, possible high performance rebuild, and a converter; you can also swap in underdrive pulleys for some additional HP.

Have you done any intake mods? You can cut out the baffles below where the air filters are. Its a cheap way to increase the air flow.

I've descreened the maf and cut the baffles out of the air box. I haven't touched the TPI. My transmission is working fine now and the car has 108k on it but someone swapped out the 2.77s and didn't replace so the speedo has been registering fast which means more miles showing on the car. What about adding the cooler and a trans go kit for now and run it until it gives? I've always heard if you change the fluid in a high mileage tranny it'll more than likely go out right after though. What do you guys think?