Hi,
I know this topic often divides opinion on car forums, but I've always felt my 6 speed manual 05 3.0i SE was a little long geared for a sports car from the factory with its 3.07 Diff. This feeling was further compounded when I fitted the M spec tyres with their extra 5% of profile. This had the effect of increasing it further to something akin to the 2.93 fitted to the E46 330I.
Looking on Realoem it became apparent that BMW had probably thought something similar as the post facelift 3.0si had a 3.23 in the roadster and a more aggressive 3.46 in the coupe. I then started looking into the gearboxes themselves and realised that all the 3.0i/Si and even the M use the same basic 6 speed gearbox with the same (or virtually the same in the M's case) ratios. So bearing in mind I'm running the same size tyres as an M I thought I'd look at what ratio diff that uses, it has a 3.62 which is basically the same as the prefacelift auto 2.5 and the 3.0si autos 3.64.
So I thought sod it, for a £100 or so from a breakers and a hours fitting I'd try a 3.64, at the end of the day its easy enough to reverse.
It took a bit of finding but i eventually found one, fitted it and the cars certainly pepped up, much more lively now and more akin to what it really should of been from the factory.
For anyone thinking this is a bit of an extreme mod, its worth bearing in mind that after accounting for the different tyre profiles between the M spec and standard, a 3.64 diff with M spec tyres gives basically the same gearing as the 3.46 does in the manual coupe with standard sizes and I've yet to see someone complaining that a Z4 3.0SI Coupe or a M is too short in the gearing.
The only detriment to this mod is my 6th is now the equivalent of what 5th used to be, but again its only the equivalent of what the prefacelift 5 speed 2.5i are running from the factory anyway and its really not that intrusive. done a good 30 mile stint on the motorway now with cruise on and at a decent pace its fine, doing about 400rpm more than it used to for a given speed.
I know this topic often divides opinion on car forums, but I've always felt my 6 speed manual 05 3.0i SE was a little long geared for a sports car from the factory with its 3.07 Diff. This feeling was further compounded when I fitted the M spec tyres with their extra 5% of profile. This had the effect of increasing it further to something akin to the 2.93 fitted to the E46 330I.
Looking on Realoem it became apparent that BMW had probably thought something similar as the post facelift 3.0si had a 3.23 in the roadster and a more aggressive 3.46 in the coupe. I then started looking into the gearboxes themselves and realised that all the 3.0i/Si and even the M use the same basic 6 speed gearbox with the same (or virtually the same in the M's case) ratios. So bearing in mind I'm running the same size tyres as an M I thought I'd look at what ratio diff that uses, it has a 3.62 which is basically the same as the prefacelift auto 2.5 and the 3.0si autos 3.64.
So I thought sod it, for a £100 or so from a breakers and a hours fitting I'd try a 3.64, at the end of the day its easy enough to reverse.
It took a bit of finding but i eventually found one, fitted it and the cars certainly pepped up, much more lively now and more akin to what it really should of been from the factory.
For anyone thinking this is a bit of an extreme mod, its worth bearing in mind that after accounting for the different tyre profiles between the M spec and standard, a 3.64 diff with M spec tyres gives basically the same gearing as the 3.46 does in the manual coupe with standard sizes and I've yet to see someone complaining that a Z4 3.0SI Coupe or a M is too short in the gearing.
The only detriment to this mod is my 6th is now the equivalent of what 5th used to be, but again its only the equivalent of what the prefacelift 5 speed 2.5i are running from the factory anyway and its really not that intrusive. done a good 30 mile stint on the motorway now with cruise on and at a decent pace its fine, doing about 400rpm more than it used to for a given speed.
1066 Country
