I have an 88 gt automatic. My tranny is shot and I was wondering if i should rebuild it, of rebuild a C4 for it. My goal is to ease my way into the 13s. I like the AOD only cuz of overdrive. Gas mileage is somewhat important to me, but i know it is sacrificial to any major mod. However, I was wondering if I shud rebuild a C4 and put a lock-up converter in it. Wud my gas mileage significantly decrease over the AOD? I want a tranny that will also perform and hold up for some weekend track time. Any idea as far as gas mileage with a C4 and a lock-up converter? I'll be running 3.73s out back.

 

c4 is just about the same as the aod in terms on internal gear ratio. the c4 has a 3rd gear ratio of 1.00:1 just like the aod. at 60mph, 26.1in tire (255/50/r16 MT ET Radials) and 3.73's, & c4 rpms would be around 2800-2900 (using this calculator here ) at 70mph 3300-3400rpms... at 70mph and aod u get around 2200-2300... OD lowers ur rpms about 900rpms. i checked w/ my aode today.

 

T5 swap

 

No t-5 for me. I like to bracket race.

 

but how much rpms does it drop when the torque converter locks up?

 

im not too sure on that. i dont think its a whole heck of alot. when i locks it provides a connection much like a t5 would have. its direct connection so theres no slip which means alot less heat. it only locks at cruise and right after a shift. i would get a lock up no matter which tranny u get. i plan on bringing my car to the tranny shop tomorrow or wednesday to get it rebuild. i came so close to getting a c4 setup but i realized how much gas i saved when i drive to work w/ the OD on instead of no OD. needle barely moved with OD on.

 

If your going to braket race I'd stay away from a t5 unless your suspension is really dialed in. Its a lot easier to keep your launches consistant with a auto. I personally would do a c4 especially if your running brackets. c4 is cheaper to build, lighter, easier to install if doing it with the car on jackstands, clears longtube headers. Downside is it doesn't have overdrive, but as long as gas milage isn't an issue a c4 is the way to go.

 

Its just that, i can install a C4 with a shift kit right now. But if I did the AOD thing, I'm going to be waiting a couple weeks. So, I don't know if the AOD thing is worth the wait, or just put in the C4.

 

I'm going to be going from a t5 to a c4 soon. I'm trying to pay my tool box loan off so I can take another loan out and get a good c4. I'm going for one with a brake and everything.

 

what's more dependable? the C4 or the AOD?