67mustang302

5th is nice for a street car that sees road courses. 1-4 on the track and 5th saves gas and wear when cruising on the street/highway.

Scott H.

It works good on the track too (depending on the track) with limited horse power cars. Running a high numerical rear end gear closes up the gaps between gears, so the car is always in the meat of the power band. The down side to this, is the engine gets it's guts screamed out, or top speed is limited.
On smaller tighter circuits, it's not a big deal. But there are a lot of really fun fast tracks, where I've seen cars bouncing off the rev limiter half way down the back or front straight. Which is why the aftermarket race transmissions are coming with more gears now.

.boB

For road racing with 350hp, you don't need much. And that's good, because you'll save a lot of money and weight, and driving it will be easy.

Any one of the aftermarket T5 rebuilders will be able to make what you need. I know some guys in AI and CMC who just buy used transmissions at the bone yard. They run them a couple of seasons, they break, and they install a new one. They carry a spare, and can change them at the track pretty quickly.

For my 500+hp street/track car, I use a Tremec TKO, one of the "older" models. It was more expensive than a rebuilt T5, and it'se heavier. But I've been beating the snot out of it for years, and it still shifts nice and smooth. I like the way it shifts better than my '08 Mustang. I put it in once, and have never removed it. I change the oil twice a year.

67mustang302

You don't really need that many gears. The trans gearing dictates what rpm range the engine operates at. While final drive gearing will help by making the whole car more responsive, the trans dictates where the rpm will be when you shift. Having more diff gear helps you run up through the rpm faster. There are still a LOT of road race cars out there that run only 5 gears, some run 4, and some run 6. Generally the narrower rpm the engine operates in and/or the higher mph it sees, the more the gears. F1 cars run 7 speed sequential units(but they also operate at 18,000rpm and over 200mph) and most road race cars in GT racing run 5 or 6. It also depends on engine setup, the broader the power band in the engine, the less gears you need...which can be beneficial to a less skilled driver, since it's less need to shift and harder to get the engine to fall out of it's power band, making it easier to concentrate on driving.

Often for the typical amateur driver, a 4 speed with an engine that has broad torque will be faster than a 5 speed in an engine with a peakier power band.

.boB

This is very true. On the track I only use 2 gears - 3rd and 4th. I have a broad enough torque band there's just no need to use any other gears.

I use 5th (.64OD) on Miller's very long front stretch. At 135mph, I don't have enough torque to go any faster in 5th. But I don't lose any speed either. But it's nice to let the engine cruise along at 4,500rpm's for a few seconds. Helps to control heat and burn less fuel.

I think if I had a .80 OD, I could gain a little speed there.

_RY_

I spin 28 inch tires. I was driving at night and my tach light had a loose ground at the time so I cant be sure, but I think it was 5500-6000. I'd tell you the speed, but my tranny has no drive gear lol