Differential selection question
 

I've got a street driveable track car and want to get some gearbox and differential advice about.

It has a 1.6L with the original 5speed and a 1.8L 4:30 Torsen swap that I've run for a few years when my car was NA. (I rebuilt a 94 Torsen with 99 NB 4:30 ring and pinion)

Now I have moved on to a turbo that I intend to make reliable power in the sub 200hp. I've just started the process of getting the MS system in but I have done a few events with the stock GReddy setup (6deg timing and rising rate fuel reg) and the car is not very fun because it only really makes power at high revs and then I immediately have to shift and wait for the power again.

I know a lot of this will be helped with the MS that can control timing and being able to turn up the boost over 3psi but I know I'm eventually going to need better gearing.

I've got another 94 Torsen with standard 4:10 gearing and was thinking about using that and my 5speed.

Is that a good way to go? Keep in mind that this is not a DD and I only drive it on the hwy to get to track days so I'm OK if it is not the most gas efficient setup in the world.

Do you run out of gear on the track? If not, keep it lower, accelerate faster. If you need more headroom, then 4.1

just my opinion.

I feel like I am but maybe I'm just getting up to that rev range fast and need to shift. I have an aluminum flywheel so it always seemed to get into the revs quick when it was NA (the only way to accelerate with the 1.6l naturally aspirated engine).

I keep hearing that the best transmission for turbo is a 6 speed (is this because of gearing or strength?) and it should be paired with a 3.9 but I also noticed that the Mazdaspeed Miata is a 6speed paired to a 4.10. I've also heard that people have traction problems with 4.30 and boosted power.