Tranny first gear combined with rear gear help

It depends on chassis.

The T-5 was available with 3.35 and 2.92 first gear in the Mustang.

On the street, I always found the 3.35 to be a bit of a granny gear. With any rear cog to speak of, you would be shifting to second at 5mph or so.

However, it is worth ET at the track.

The OD with a stock T-5 is only a .68 ratio, so I'd stick with the 3.91s. It'll make highway driving more pleasant, and you won't give up too much at the track.

As far as stock T-5s holding up behind 500hp. Well, maybe. In my experience, the only stock T-5 that would have a chance of doing that for very long would be a World Class, which yours isn't, and one of those would take it, but not for very long. There are aftermarket gearsets (G-Force and others) that will hold that kind of horsepower for years though, and a T-5 shifts way better than a TKO.

the most important thing for making a tranny live is getting a good clutch. You don't want (or need) some hard hitting ridiculous thing, especially with a drag radial tire. Mcleod makes several good units these days.

Also important is some good synthetic fluid with anti-clash additives like Royal Purple Synchromax or Red Line ML.

These guys: www.promotionpowertrain.com built me a lot of nice stuff when I was racing Mustangs, and they know their way around a T-5.

They usually have some good rebuilt stuff for reasonable pricing also. You could get a world class unit with the highly awesome .59 OD ratio for pretty cheap (you have to ask for the good OD). In a Mustang, I ran that ratio with a 4.30 gear and at 70 mph, I wasn't even hitting 2500 RPM with a 26" tall tire.

Good Luck

Steve