Gearbox Upgrade

Ashm330 · Post by **Ashm330** » Mon Dec 03, 2012 10:03 pm

My NA 1600cc turbo MX5 is eating NA 5 speed gearboxes. Has anyone successfully adapted a RX7 turbo FC or FD gearbox into their MX5? Or does anyone know a good upgrade that will last more than a couple of weeks pushing 300+hp?

Mad Kiwi · Post by **Mad Kiwi** » Mon Dec 03, 2012 10:33 pm

Common mod is the mx5 6 speed. I have just done it and it seems okay.

Miata turbo guys reckon 400+ hp is the limit and they suspected much higher at one point...haven't kept up researching since awhile ago but certainly enough for most 4 cyl turbo mx5's...

As is commonly said, it's little more notchy than the 5 speed (must try the motorcraft oil everyone is currently raving about..) but it's allright.

I was all concerned with diff ratios etc but the fact is (from what i can tell) a 4.3 to a 4.1 is about 150 rpm and then 150 rpm again from a 4.1 to a 3.9 (approx).

So the difference is not huge. I haven't really noticed any real world difference in my car.

Mine is a 4.1 and I have a 3.9 ready to go in but for 150 rpm i just can't see the hurry....

Post by **jif** » Tue Dec 04, 2012 10:35 am

there was some talk that the RWD Millenia (?) gearbox was a solid replacement. Better tooth alignment. There's prob some pics somewhere of shredded and clearly unaligned miata teeth .

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last_resort14 · Post by **last_resort14** » Tue Dec 04, 2012 3:15 pm

6 speed is the easiest choice.

out of curiosity, what are you breaking on the5 speeds?

Kieran · Post by **Kieran** » Wed Dec 05, 2012 10:31 am

6 speed is an easier swap and if you break that I want to know what your running in a mx5 to break it or you arent shifting correctly

Ashm330 · Post by **Ashm330** » Thu Dec 06, 2012 12:04 am

[quote="last_resort14"]6 speed is the easiest choice.

out of curiosity, what are you breaking on the5 speeds?[/quote]

It's running thrust bearings on the input shaft, and chipping teeth off 4th gear

last_resort14 · Post by **last_resort14** » Thu Dec 06, 2012 8:33 am

input shaft bearings are just an mx5 thing. had lots of boxes get noisy as, and synchros getting munched. never actually broken any teeth though.

SLYDIT · Post by **SLYDIT** » Fri Dec 07, 2012 7:05 pm

Ive had 3 gearboxes and all have bad input shaft bearings. Just about time for number four.

Mad Kiwi · Post by **Mad Kiwi** » Mon Dec 10, 2012 7:25 am

Can you not get the input shaft bearing replaced......?

Too expensive...?

Gearbox Upgrade

Gearbox Upgrade

Gearbox Upgrade

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