Best OEM final drive for 5 speed T25/2554 DD/AutoX/HPDE
 

So, my car is daily driven, and will be used for 4 Autox a year or so, and HPDE like twice a year. 5-speed, and guestimated final numbers should be a round ~225ft-lb, 235hp.

I'm considering swapping my 4.30 to a 3.90 to have a little longer in each gear. I have an offer to trade my diff flat out, though mine has 72k on it, and the mileage on the 3.90 is unknown. Otherwise, his asking price is $500 without the carrier. Looking to hear from people on both sides, as most people I've asked their opinions are running a 4.10.

My fear is, as far as enjoying the turbo DD, I'll lose some of that *back of your seat* feeling at this power level. I expected fuel economy gains on the highway, but in reality, I will only be going from 4080rpm@80mph to 3709rpm. So, not really all that much of a change.

AutoX I think will be benefited by having a higher top speed in 2nd gear.

I can't speak for HPDE, as my first event is in May.

So, Tl;Dr: What is your ideal final drive for a T25/2554 setup with a 5 speed, that will be daily driven, with bimonthly autocross time, and semiannual HPDE?

I'm about to pull the trigger on a 3.9 r&p for like $90. Its no 3.63 but I think it will help with dding.

I'd switch the 4.30 for a 3.90 if it was straight across that's for sure.

True. That's a steal.

Is it? From what I'd heard with the 4.30 becoming Spec Miata legal they were going up in price.

maybe.
but the 3.90 is better.
so who cares lol

I liked the 4.10 with the 5spd in my similarly/slightly more powered 95. Doubt a 3.9 would ruin the car at all.

thing is, when you turn the boost up, and you will turn the boost up, and break the 5sp, and you will break the 5sp, and get a 6sp, you'll be so much happier with the 3.9

For autocross 5speed +turbo power plus DD and a few hpde not too ridiculously high RPM limit you want the 3.909. with the rev limit turned up above ~8000 rpm the 410 would be faster and better use of the power band.

See the problem is, as I know you personally have made evident, stock rods and 5-speed are good friends. lol.