Because if you plan on lightly modding or even some heavier mods 3.73's can be too much for a TPI car especially at high RPM's. Wanna shift into 4th at the end of the 1/4??

 

4th isn't a big deal to me. I'll definitly be hitting 4th with the 3.55's in my mustang, so that doesn't make a difference to me. I mean, 3.73's would be difficult due to the low end torque, but they snuff out up top... but I mean, it's a heavy car too.

 

I think the highest I'd go with TPI is 3.45's. Gears from 3.27-3.45 match the way the setup makes power the best. I've heard of people putting in 3.70-3.73 gears and not liking it. They liked the launches, but that was it. They also didn't like to drive with on the highway too.

 

That's where the double overdrive of a 5th and 6th gear come in. It's not like 4.10's or anything...