well you can go 4.11 or lower (higher numbers means lower ratio).

the higher the number the more acceleration you will get to a point but then it depends on your gearbox ratios as well.

so, for example, you might make say 40mph in first gear with your current rear gears at 2.78 or 3.00. If you change it to 4.11 it might only be 25mph in first but it will get there quicker. Theses are not actuals!!!

Speed at 5000rpm in top gear for a c4, based on 205/60/15 tyres - these are pretty close estimates.
2.78 - 132mph
3.00 - 122
3.55 - 103
4.11 - 89
4.56 - 80

its really your choice. 3.55 is a good compromise. 3.73 is popular with o/d trans and 4.11 up is normally drag racers who can and do pull waaaaaay more than 5000rpm.

if you never drive on the highway and you dont care about your gas bill then 3.73 or 4.11.

 

Would a t5 tranny swap help get better numbers than the c4?

 

better which numbers?

a t5 or an AOD gives you an overdrive gear.

So, for example, if you have a 4.11 rear end. C4 in Drive is 1:1 so you get your 5000rev speed of around 90mph. With an overdrive, you get a final drive ratio (varying) ofaround 0.8:1.

So times the 4.11 by 0.8 and you have effectively a 3.3:1 ratio or say around 110mph at 5000.

it depends what you want the car to do. if its just blasting off the lights then beef up your c4, add a stall converter and change the gearing to anywhere between 3.5 -4.11. It will be cheaper than going to an overdrive trans and arguably stronger too.

 

I will probably go with the 3.55 and stall converter, If ever take the car to the track which gears will get me faster time, the faster launch gears or the 100 plus gears?

 

A t5 will allow you to run lower gears, also a manual box eats less HP than an automatic so yes you could feel a performance upgrade with a T5

Have you done any thing to improve the ignition?? A hot ignition can go a long way to improve the power of a engine

 

There is a good 5 page article HERE about for some power gaining tips without spending a lot. enjoy

 

my 65 with AOD, 3.00 open dif ran 15.8 at 93 mph 1/4 mile 5500 ft elevation
my 65 with AOD, 3.80 lsd dif ran 15.8 at 88 mph 1/5 mile 5500 ft elevation

so i put in a 347.