Gearbox question.

[Red_Bullet]

So, I broke my gearbox. Driver error!

Running boost.

Is NA6 box same as NA8 box. Same as NBA? What differences?

Is 6 speed much stronger than 5 speed?

[Red_Bullet]

Might have partially answered my own question.
https://www.miata.net/garage/KnowYourCar/S8_Gears.html

[manga_blue]

I've broken four 5 speed boxes in mine. The weakest point is the shift mechanism. It's easy to get it wrong in the heat of competition and bend a fork.

Mazda kept the internals the same through NA6, NA8 and NB8A while progressively modifying and strengthening the shift system. I found my NA6 box the lightest and nicest to use while the NB8A was the most solid, albeit a bit dead compared to the NA ones.

[Todd77]

What power you running? Seriously if you have 250hp and up you will keep mincing 3rd gear. Also depends on the grip you have. I did 4 boxes in 5 race meetings, it has nothing to do with shifting ability. The gears are not strong enough. Mine stripped the teeth off the gear each time half way thru the pull in third. I got sick of changing boxes and went to rx7 box, bit of a stuff around but better than breaking boxes all the time.

[speed]

What power you running?

I'd be interested in knowing this too.

I got sick of changing boxes and went to rx7 box, bit of a stuff around but better than breaking boxes all the time.

FC or FD and what else did you need to change? Bell housing, tailshaft?

Thanks!

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[93_Clubman]

Solomiata also has info about RX7 GBs for MX5s (3/4 down page): http://www.solomiata.com/Drivetrain.html

[beavis]

Is NA6 box same as NA8 box. Same as NBA? What differences?

Fundamentally all NA/NB gear boxes are interchangeable.
All the 5 speeds are basically the same, with small differences in the shifter and the like.
The 6 speed is stronger, however has less feel. again there were a few variations in the shifter over the years.

Is 6 speed much stronger than 5 speed?

Yes

Also note the Starter motors differ, with the starter motor included with the 6spd equipped cars being smaller and lighter and runs a slightly different bolt patter.

[Red_Bullet]

Thanks for the good info provided above. I was running a short circuit event with a standing start, lots of 2nd gear stuff, one short downhill 100 metre run in 3rd.. I have around 200 WHP I think.

Run 1. Made mistake off the line, too many revs, 2 nice black lines off the starting line, thought I spied some tyre smoke in rear view mirror . Completed run. I figure I may have damaged the box with this start, although nothing was obvious until next run.

Run 2. Much more sensible start, lots of throttle induced oversteer in tight sections and second gear . Gearbox failed in second gear . Running a Rotrex c74 supercharger, 10 pounds max boost at redline, power output/torque curve is quite unlike turbo, midrange is . Boost is related to engine revs so only builds with crankshaft speed. I have not seen inside the box yet so no autopsy available yet.. It's at Automotive Plus having a transplant to another lower km 5 speed NA8 box. No 6 speeds available at present.

It hasn't been on a dyno since I fitter MS3Pro, but with original Rotrex install by previous owner and XEDE piggy back it produced 200 WHP. With the MS3Pro it may well be producing more.

I should dyno it if I can find somebody around here (Brisbane) who knows mx-5's and isn't allergic to Megasquirt!

[Todd77]

What power you running?

I'd be interested in knowing this too.

I got sick of changing boxes and went to rx7 box, bit of a stuff around but better than breaking boxes all the time.

FC or FD and what else did you need to change? Bell housing, tailshaft?

Thanks![/quote]

320hp on high 270 low boost, broke the boxes on low boost every time, my brothers car running 250 on semi slicks ran 5 track days, I put my slicks on it and it lasted 3 corners before stripping 3rd. I'm running fc turbo box as ratios are the closest to Mx5. Adaptor plate, tailshaft, crossmembers for box and diff, clutch plate. But fit and forget, rx7 boys aren't breaking them at 500. It's worth it in long run. All info on the net mate

[speed]

I'm running fc turbo box as ratios are the closest to Mx5. Adaptor plate, tailshaft, crossmembers for box and diff, clutch plate. But fit and forget.
All info on the net mate

Thanks, I looked at the link that was posted but that didn't say what was needed to convert, more on interchangeable stuff inside the boxes.

I'm guessing your using a rx7 diff as well since you stated crossmembers for diff and box.

I don't have the power that you guys have, just know that my box is the weakest link.


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[Todd77]

No im running Mx5 diff, it's just that rx7 box doesn't have provision for power plant frame. So you have to make a mount for diff( rubber mount preferably) solid mount causes vibration and a crossmember for gearbox mount. Google rx7 T2 gearbox in Mx5, it all should come up.... cheers

[The American]

A 6 speed should be all you need. The custom work required for Rx7 transplant - you'd want to have large power goals and plans to make it worth the effort.

[speed]

No im running Mx5 diff. Google rx7 T2 gearbox in Mx5, it all should come up.... cheers

Thanks, appreciate it

A 6 speed should be all you need. The custom work required for Rx7 transplant - you'd want to have large power goals and plans to make it worth the effort.

Your right and although I will be chasing more power, I suspect that I won't ever be going large enough to warrant the transplant in my current car.
That said, I do like to learn and understand what is available and what needs to be done if ever I was to spend up big.

Thanks guys



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[NitroDann]

300ftlb through 6 speed is a ok.

Dann

[Todd77]

300ftlb through 6 speed is a ok.

Dann

Patrick's broke mid pull in 4th