Blown Transmission
 

Hey everyone,

I am looking for some advice please.
I have a 1990 Miata with about 350/360 rwhp. I managed to destroy the transmission yesterday and I wanted to explore my options.

I installed a lower ratio(?) gear box into it about 3 years ago and this made it drive nicer, lowering the revs and making first gear somewhat useful.

What would be my best option to replace this ?
A 2004 MSM transmission (if I can find one that is !) - would that even fit?
A lower ratio gear box ( assuming it was from a 94-97 1.8 NA?)

Any other thoughts?

Thank you for any help you can give ....she is in the shop and I would love to get her back out while we have sun ( I live in Minnesota :) )

Cheers Mark

What transmission did you have in it that blew up? 5 speed or 6 speed? You really need a 6 speed, but at your power levels you are at about the top they like. KMiata is working on swapping in a BMW trans that should hold all the power, but no ETA on those yet.

Hey there,

It was a lower ratio 5 speed tranny.

Would a 2004 MSM fit it ?

Its in the shop so I need to get it moving asap really.

Thank you

The MSM transmission will be stronger than the stock 5 speed. It will fit. Will require a different shifter though and a short throw setup will likely not work if you have one on there.

At your power, this is a good option.

Yes the 6 speed from the MSM will fit. It will require the shifter to come with the trans. Only 2 bolts will fit with the starter.

And go ahead and also swap the NA starter for an NB starter, if you haven't done it yet. The NB one, is lighter! ;)

Any 99-05 6 speed transmission will fit and hold about 100ft/lbs more than a 5 speed.

Is anyone going to point out that there isn't a lower ratio 5-speed out there? There were some minor upgrades to the 5 speeds over the years but they were identical in size and ratio's. Not sure what you had, or thought you had.

With all that said you need two 6 speeds, one to get going and one to replace that one in 6 months.

Also how did a 5spd hold up to anything like 350whp for more than a dyno session?

You can contact Jason at JO Motorsports and send him a 6 speed. He offers treatments for the gears that should increase the torque capacity. It's still not your end solution, but its the best one for the money, imo.

He might have extra solutions, to hold the power better. He only built mine to resist fast shifting and 250wtq in racing.

Mechanical sympathy

It should also be noted that top gear in the 6 speed is about 4% shorter (numerically higher) than top gear on the 5 speed. In addition to having an extra gear to shift through, the 6 speed won't fulfill your quest of lower revs. 6 speed cars came from the factory with a taller diff ratio to compensate for this.

The 6 speed will, as has been said a few times, be considerably more resistant to grenading itself under high power.

Hi Everyone,

I meant that the diff had a lower ratio 3.63 I believe not the gearbox LOLOL

Would a NB 5 speed gearbox best a good option then ? compared to a NA 5 speed?

Thanks

Nope, they tend to blow apart at ~225 ft/lbs. The 6speed seems to live for a while in the low 300 ft/lb range.

I'm still confused, you seem to be asking about lower ratio differentials.....did you break the thing with the shifter sticking out if it? Or the lump in the back with the axles?

The gear box man ....I was confused Sorry

Yeah, grab a 6 speed. If you have the 3.63 rear end, the 6 speed/3.63 is a great set up. Myself and several others are running it and love it.

All 5 speeds are the same gearing and hold the same power level. Only minor differences in synchros existed between some 5 speed models but they don't effect power levels.

All 6 speeds will hold more power than all 5 speeds by a very good margin.