99mx5

iTrader: (16)

I have a 6-speed and a 3.9 diff and am thinking of upgrading to a 3.63. Thoughts?
I'm mainly looking to have my gears more usable on the track.

Downmented

iTrader: (1)

https://www.flyinmiata.com/tech/gearing.php

The Australian

I have a 3.63 and I would not want a 3.9. 1st already feels too short.

Madjak

You don't usually use 1st at the track. I found the gearing is best if you can make 3rd to 6th useable so you are only using the right 'H'. It avoids the 2nd to 5th mis-shift which is common with the 6 speeds on the track. I can't imagine how a 3.63 would be quicker than a 3.9.

18psi

iTrader: (76)

It's definitely an improvement, IMO.
I'd do it in your situation

Ben

iTrader: (33)

Not sure if I agree in this context, as it does not change the gear ratios, and the issue I think he's having is how close the ratios are on the track. With his power levels, he probably wants wider gears, as he makes the torque to pull wide gears. A 5-speed wide Quaife box is probaby the real solution here, but $$$$.

18psi

iTrader: (76)

Oh yeah a different box is a better approach, but the affordable "solutions" are still in development infancy.

99mx5

iTrader: (16)

Thanks for the replies all. Currently, the ratios are short and close. I figured the 3.63 is the best bang for the buck in my situation.

pdexta

iTrader: (17)

I've looked at the 3.63 and considered it in the past, but it was tough to justify the total price for such a small change in gear ratio.

Add up the cost to buy the gears and have them installed, then you've got a leftover 3.90 ring and pinion with minimal value to it. That gets you a final setup that's no stronger than where you started and slightly taller gears.

Compare that with a V8 roadsters getrag conversion, plus a getrag diff in one of many awesome ratios that's much stronger than stock. Then subtract the money you'd get from selling your full 3.90 torsen setup.

When you do the math those prices start getting awfully close for what seems to be a much stronger setup with way more options.

Savington

iTrader: (31)

Do you have specific corners at your local track that you are having problems with? Wheelspin in 3rd or running out of gear in a specific place? IMO 3.63s have a really narrow use case for track cars, and at your power level, I would expect 3.9s to be faster unless there's a specific corner or corners which would benefit from a taller gear.

HHammerly

iTrader: (3)

I just installed a set of 3.6on my car (6speed) i really like it on the street, it will also keep me form banging on the limiter every lap (47sec) at my local track where i run the most often. We will see how it goes, next track day is on the 30th.

99mx5

iTrader: (16)

I do. I'm trying to reduce the need to downshift and have gears that have a wider range.

codrus

If you're competing on the track, then the question of 3.6 vs 3.9 depends on the track, power level, grip level, a zillion different things. It's hard to generalize

If you're doing track days, 3.6 vs 3.9 makes little difference.

If you're doing autox, 3.6 is a fairly big win over 3.9 because on most SCCA-style courses it will mean a lot fewer shifts into 3rd.

If you're driving around on the street a 3.6 is a lot less annoying than a 3.9.

--Ian

Lokiel

This post earned you a Pos-cat from me, useful information AND almost excellent grammar and punctuation!
(you missed a comma after "the street" in the last sentence, used "autox" instead of "auto-cross". and ", a zillion" should be " and a zillion", if "zillion" can be considered a word)