mx5cartalk.com

Hi guys,

I am sure this has been covered many times but the search function brought too many results.

I've read that the NB SE has a "strengthened gearbox".
Is this some sort of marketing gimmick where Mazda upgraded some irrelevant part just to make this claim or was there a significant upgrade?

From MT.net that's been quoted everywhere:

"Mazda touted the MSM transmission as being shot-peened, and as such it is believed to be stronger, however, no evidence exists that non-MSM 6-speeds are not also shot-peened, and there is no evidence of non-MSM transmissions breaking where a MSM wouldn’t."

All Aisin 6-speed geaboxes are shiite on NBs and they're not great on other models/brands either, including the Toybaru (the autos are supposedly OK).

Don't know much about any improvement to strength, but considering how many shifts I mess up with this gearbox, I reckon I'll wear it out faster regardless!

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FWIW...

I can say only from my experience that the strength of the SE box I had was good up till I pushed the output past the 300+ rwhp mark. That was not tracked, daily driving with some winding backroads play. I would say in hindsight if your looking at using or continuing to use the SE 6 speed box and your goals are up to 250rwhp it would be safe and strong enough, but if going beyond that have a look at other options out there.

I have worn out a 6 speed box after 10,000 track km no idea how many kms were on it before I got it. I was only making 200 RWHP.

Then kens NA8b has over 450rwhp.

It can't last forever but it has half a dozen race events and 150 dyno pulls on it so far.

Dann

Check the speedo for how much power you can get through one with careful torque management.

Is the 5 speed stronger than the 6 speed?

I haven't bought an MX5 yet, but I am considering one as a weekender since they are so cheap, but I think I would eventually turbo it and one day perhaps it'd end up being a track toy.

As such I don't know which is the best option for me, but I am settled on the NB series.

Sirois wrote:Is the 5 speed stronger than the 6 speed?

No, 6 speed is much stronger. Though many consider the 5 speed to be the better feeling gearbox. If you're looking to make 220-270whp (or more on a built motor), you'll want the 6 speed.

NitroDann wrote:Check the speedo for how much power you can get through one with careful torque management.

Yes this is one solution, but it is a 'band aid' to the issue of building a motor that is more powerful than the driveline can take.

This issue has been discussed at length in other places. For example some clubsprint cars have gearboxes/diffs worth more than some other entrants whole car! If the rules were such that only OEM gearboxes and diffs could be used then you would not see cars with such massive amounts of power.

People should factor in beefing up the WHOLE car when increasing the power over stock. Just my opinion.

Kens car uses stock everything except pistons rods and valve springs. Additionally the chassis itself cannot take much more torque so I believe it's a nice balance.

Dann

I definitely wouldn't want more power than the stock drivetrain can handle.

I've dríven an NA on 14psi and it was plenty fast.

An NA on 14 PSI would require judicious use of the right foot to not break a 5 speed box. I broke one on 10 PSI. Stuck another 5 speed in it as a 6 speed wasn't available at the time. Got hold of a 6 speed later on, it's sitting on the shelf for next time.

It was only street dríven... made 176kw atw.
It was floored a fair bit but no harsh launches or dumping the clutch