I have a 90 with a 99 1.8, 99 six speed and FMII turbo. Rear end is a 3.9. It was supposed to be a 3.63 but that’s another story. Not happy with the gearing. Originaly I was going to go beyond 250whp with a built engine, now I will stay below 250, so the extra strength of the six is not needed. I have a 2004 car with a five speed. I was going to swap them to get a better match to the turbo and give me something to do in the stock 2004 while it doesn’t accelerate. Anybody been down a similar path? Am I wasting my time? It is a street car only.

 

At that power level it should be fine, and you will enjoy the gearing more.

The 6 speed may help the other naturally aspirated car accelerate better, too.

 

As a bonafide hater of the Miata 5 speed, this thread makes no sense to me.

 

I much prefer how my 5 speed FM2 car felt vs my new MSM. I plan on putting the 5 speed I have sitting in the garage into the mazdaspeed when it's due for a clutch. Longer gears, more time to enjoy boost. 6 speed makes perfect sense for NA.

 

Although you seem to have difficulty in getting to the point, l presume you think I should just suck it up and get a 3.63. Paid for a 3.63, got a 3.9, several years too late to bitch about it, actually didn’t get installed until last spring. Do you hate the 5 at any power level?

 

Yes. The gear spacing is inferior to the 6spd.

As far as shift feel, i don't like it there, either. Feels vague compared to 6 speed, but that's personal preference and not math.

If it were my car at those relatively low power levels, i'd keep the 6spd/3.9 combo. Again personal preference, but i'm good without a 3.63 until around 300whp. 5spd/3.9 sounds ultra gross to me, but again... personal preference.

But also you'd never catch me swapping a weaker part in place of a stronger part for any reason. Again... personal preference. Your car, you do you, i'm just saying the thread confuses me.

 

I much prefer the 5 speed. It shifts better and easy to find reverse.
I would still be rocking the 5 speed if it didnt blow up at the last track day at 250hp 230ftlbs.
Stripped 3rd gear.

Now have a 6 speed with a 3.6. Good gearing, shifting 2-3 and 4-5 is not as crisp as the 5 speed. And god damn it's hard to shift into reverse.
Takes several tries to get it fully engaged in reverse.

If mostly street car with about 250hp. I'd rock the 5 speed.

 

Ouch. Sorry to hear that. How much did you pay for the 3.63 ?

 

Too much considering I started with a Mazdaspeed 4.1..... So I paid way too much to accomplish......... nothing. I believe the shop subbed it out. Either there was a miscommunication, the tech can’t count, or less likely, didn’t give a ****. They did paint the front a nice silky black though.

In any case, if I was running the shop and someone came in complaining now my response would be along the lines of “You brought this in when?, and have put how many miles on it?” Sorry, that boat has sailed, and I already spent the money on midget hookers in Vegas.” Or something like that.

 

I'd just get a 3.6 rather than go back to a 5 speed.

You've already got the stronger part, why replace with a weaker one? (even if the car wont hit a power level where it will break)



Plus, a 3.6 ring and pinion is heaps cheaper than a 5 speed. (unless the Canadian market is weird)

If they're hard to find up there or whatever, look for them on the Aussie market.
3.6 was the standard ratio for us post'00, so they're common as hell, and usually $100au or so, if that (hell, i've seen assembled 3.6 opens sell for $150). Plus whatever postage would be up to the land of poutine.

 

working 5 speed transmissions can be bought for $100-250 all day long.

3.6 Gear only cost around $400-450 shipped to the states, plus about $400-600 to have them properly fitted/back lashed/shimmed into the diff, by a shop.

OP, how do you know you have a 3.9 and not a 3.6?

I just put in what i believe is a 3.6 torsen with a 6 speed transmission, and 3.6 NB speedo gear, and my speedometer reads about 6-7% above actual GPS speed.

So either i too have a 3.9 torsen or the Miata speedo gears are not accurate.

 

Unbolting it from the housing and counting the teeth is the best way to tell.

 

yep, count the ring gear teeth and the teeth on the pinion gear and divide them to get the ratio.

 

Also kmiata has a gear ratio calculator, at 80mph in my 3.909 and 6 speed I turn roughly 3900rpm. Use their calculator and see where you're at. Use your phone with an gps speedo app to get accurate speed. That would suck if you got a 3.909 instead of a 3.6. I really like my 3.9 and 6 speed ratios though, not sure why the OP doesn't. I think the az6 6 speed shifts much better than the 5 speed personally

 

You'll feel quite dumb when the 5-speed blows up. Not if, but when.

Buy some 3.308s for the turbo car. You'll love them.

 

Truth, I ripped all the teeth off 3rd gear just rolling on the throttle one day back when I had my old NA with a gt3271. I was making maybe 240whp at the time and it just chewed that gear to bits.

 

Aint that the truth!

i shreaded 3rd gear on my 5 speed at my last track day, on wastegate only 10psi nice and easy 2-3 shift. that is basically 250hp 230tq.

Thus me now having a 6 speed.

Ill crack open the diff in a month or two when i have time to install poly diff bushings and count the teeth.

 

At this point I will probably leave it alone for now, spring is trying to show up here in the great white north and I want to drive, not swap transmissions. If one winds up needing a clutch I might re-think it. The turbo isn’t even fully dialed in as I have not had to time to get to a dyno that has an operator that will touch a Hydra (insert ridicule here............). The 3.63 would be ideal and let me go power mad later, and what 3.308’s? The only reference I can find is B2200 gears that don’t actually fit without some serious maching. Have I missed something?

 

MFactory

https://www.miataturbo.net/suspensio...earsets-92250/

 

Thanks, I was ignoring it.... I thought it was only transmission related.