I have a 1986 T/A with a 1989 GTA 350 TPI. I have Full length headers and 3" y pipe to a high flow cat, and then 3" dual catback. I ran a 15.5....... I have 2.73 rear gears. How much time will i drop if i put in 3.73 gears?

 

You don't wanna go 3.73 with TPI. You'll wanna go with 3.42's.

 

Yep. One of the biggest mistakes is not matching your gears to your powerband. I should know I did it. Didn't gain anything from 2:73s to 3:73 posi.

Oh, and you said dual 3" exhaust, do you mean single? dual is a bit much for your setup.

 

yeah, it's dual tip, not true dual.

Could someone explain to me how a 3.43 would be better then a 3.73... how will it not drop times on my 1/4? I thought that the bigger the gears, the lower the top speed, and faster through the gears, which would lower the times....... ??

If it won't help my 1/4. What are some of the best HP increasing mods?

PS----This car will not be a daily driver. Just a something to take out on sundays and to the track. I bought this on the side because i love muscle cars, and I needed something to start learning about them on. I know most of the basics, but there are a few things im not sure about.

 

basically if you run a taller gear it will want to make power in the upper R's where the TPI is not happy, tpi makes its power on lower r's so running a 3.42 gear would get you down the track faster then a 3.73

 

so if i did a lower 4 gear like a 4.05 or sonething, that would make it even faster?

 

No, I think you missed what he said. Gears are designed to work with the engine's powerband which is usually determined by heads CAM and intake. The Stock TPI Intake has great low end torque but falls on its face at about 4500-5000 RPM (right?). Because of the short powerband, a high gear (like a 3.73 or 4.10) will keep it in gear for a very short amount of time, so most of the time will be spent shifting (not under power) because the redline will be reached sooner with higher gears. With a 3.23 or 3.42 gear, the engine will be allowed to stay in gear long enough to realize power, but the load will be "lightened" more than having a 2.73 or 3.08 gear. Hope this helps

 

Yup, what they said.

 

explained very well tonyc. If you plan on doing more to the engine, like a cam and intake, you will probibly be better off putting the 3.73 in now, rather tahn doing a 3.42, then switching later. I have a stock 3.23 rear on my car, but it would be much better of with 3.73, or maybe 4.10, but that's beacuase it doesn't even pull hard till it is above 3000rpm.

 

Thanks guys that helps a lot...

I am planning on putting in a differant cam and I'm in the process of installing a custom intake, so I think I will go with the 3.73.... Is that a good idea? or should i still go with the 3.42? thanks for the explanation though it helped a lot!!! I do see that at high rpm's it feels like it is dragging wight.

 

Also, any good upgrade ideas to increase the horses the most?

 

Now I'm not positive, but I always thought that the TPI induction just doesn't produce power past 4500 rpms and even some mods won't help too much. In this case 3:73s still wouldn't be best. I'm not positive though, but isn't that why some people go with Super Rams or Mini rams.

 

since we're talkin about about gears would i gain anything from switching from 3.23 to 3.42?