I have been doing some research on the S15 6 speed recently. It seems there is a "fix" to make the gearbox more reliable. It has something to do with the retainer and circlip that holds 4th gear in place. The modification can be done for around $500.

I am looking at using one in the Sunny, but the gearbox guy I spoke to was not sure/confident that it will hold up with the horsepower and application I want to use it for. Cheap close ratio box though, IF we can make it reliable.

They are good with a lower ratio diff such as a 3.9 or 4.11

1st 3.626
2nd 2.200
3rd 1.541
4th 1.213
5th 1.000
6th 0.767
They would be better with a 0.92 5th

Nismo do make a gearset for the S15 box. You can purchase the 6th gear seperately, it's a 0.862 OD, not sure of the cost though.

On another angle........ what about the gearbox in the new 350Z? It's also a 6 speed box, slightly different ratios;

1st - 3.794
2nd - 2.324
3rd - 1.624
4th - 1.271
5th - 1.000
6th - 0.794

Considering the 350Z has 60kw more power, 100Nm more torque and is 220kg heavier than the S15, surey it must be a stronger gearbox? They both seem to have the same model designation though - 6M Does anyone know details on strength of the Z33 box?

Also, how hard would it be to fit to an FJ20? With the S15 box, I was planning on fitting the FJ20 Bellhousing..... could this be done with the Z33 box?