200 wheel torque and it'll probably live forever. The same is probably true of a stock 5-speed, though.

--Ian

200 wheel torque is something you'll easily get out of a 12 psi build with a decent tune. From personal experience, a stock five speed will last forever at that power level, so your cryo treated six speed should be fine.

I blew up a 5 speed at 200wtq

https://www.miataturbo.net/diy-turbo...k-links-56507/

pretty good run down of power + mods... don't think it has changed much if at all in the last 4/5 years.

Super dumb question from somebody with a background in metal work, but not a great understanding of the details of how a tranny hooks up to an engine, and the other mechanical aspects of what this would actually take.
What's the real challenge in creating that conversion kit myself, assuming I have a full metalworking shop at my disposal?

Not that much, but lots of little things: figuring out bellhousing adapter, making sure clutch/flywheel/hydraulics all lined up and had proper reach. Speedo sensor. Adapter to make PPF bolt up, or custom mounts to eliminate the PPF altogether. Driveshaft. Shifter location/hole. Probably a few other things I'm forgetting.

If you think it through, it's a lot more than most here seem to think, but also not anything a competent machine shop worker/welder couldn't figure out.

Good to know. I'm starting to put together the never ending to-do list for my vehicle, and I keep seeing the transmission as the weak spot nobody can seem to figure out, so it's good to know that this is at least possible. The eventual goal is a bullet proof 275 - 300whp, I'm hoping to find a solution for the transmission issue without having to go full retard and V8 swap the car to get a proper transmission in it.
If I ever get around to it I'll be sure to document my inevitable failures for all to see.

300whp on a 6sp only becomes a problem on track. But yeah

The hard part is doing all that work and then turning it into a bolt-on kit that you can sell for a price the cheap bastards on mt.net are willing to pay. :)

--Ian

I'm not sure I'd have the RnD skills to turn it into a legitimate business, but if it's not thaaaaaaaat complicated I may be able to pull it off and at least document the process to make it semi-repeatable.

Not to derail the thread too much, but I thought the main dig on the T5 was the gear ratios weren't correct for a Miata? Also, how do they feel compared to a 6 speed? Are there short shift kits that would work for them in a Miata?

Yes, the issue isn't simply finding a solution that will hold the power, but finding a GOOD solution with track-friendly gear ratios that'll hold the power while keeping costs down.

T5 can have whatever ratios you want pretty much because of aftermarket support. Short shifter would be hard because you are already extending the stock shift location. Depends on how its done.

The basic problem is doing a good job for cheap enough.

Most of the turbo miata guys are driving turbo miatas because it's a cheap platform to go fast. A lot of the guys who can afford the development work to have a 450whp track car are driving corvettes, S2000s, GT-Rs, porsches. Your market for an expensive T5 conversion is going to be small. If there was a big market for expensive transmissions, you'd already see packages like the evo and gt-r crowd get- 10-15k for a transmission that can take 1000hp. Most of our builds (in total) cost less than that.

You are basically competing against the used transmission market. This has been a problem for so long that most guys don't even think about making 350+whp because of the headaches.... As a result, there are lots of 200-300 whp builds out there, the vast majority of which don't eat transmissions at a very fast rate. There are a handful of guys on here like bbundy that regularly destroy trannies, but they're a minority.

Sweet spot is probably a conversion that:
-solves the problem of mating to the miata clutch friction plate
-solves the problem of mating to the miata driveshaft
-solves the problem of mating to the power plant frame
-the shifter goes in the normal shifter location
-gearbox itself is something readily available but stronger than the miata transmission (ie, T5 world class)
-doesn't require fabrication- you open the UPS package and you install and never touch it again except to change clutch every few years

Why all the hype about the T5 when the TII option is available and documented? The TII is more than capable to support basically all the power/ abuse any of us would throw at it, no?

bananas

This.

This this this this this.

I was just about to ask: show of hands, how many here have destroyed even 1 six speed? How about 2? How about 3+?

The numbers are a lot less than some people think. I can only think of like 3-4 guys on this whole site that would apply to that 3rd category.

That list may be expanding in the next couple years by several hundred percent due to the development of the TSE kit and the inclusion of bigger and bigger (and more modern) turbos. Mind you, 700% of four is only twenty-eight (if my math is correct) and still not a huge number.

I know that even suffering depreciation my total build is/will be a pretty hefty sum of money and considering all the mission creep, ("while i'm in there" mixed with a hefty bit of acceptance that boost is addictive), I will be on the lookout for the next failure point. While 6-speeds are not prohibitively expensive if it means getting the car back on the road I would prefer to just spend the money on a solution up front rather than have a $700 axe hanging over my head at all times.

I will be re-reading and catching up on the transmission mega-thread going foward not to clutter this any further though.

TII has awful gear ratios and still requires fabrication AFAIK. No PnP kit available. Shorter 1st and 2nd than even a stock 5-speed, which is exactly what you don't want in a high-power car. The T5 has better ratios out of the box and you can buy perfect road ratios for it from aftermarket gear mfgs. They are also cheaper to buy brand new and cheaper to rebuild.

^this. Back to the gear ratios.

I'm less enthusiastic about this after my most recent dyno experience. No matter what we did, couldn't get significantly over 300 whp on a setup that should easily have done 350. Maybe that 350 whp isn't as easy as I initially thought it was, even with all the right parts.