Gearbox - dif ratio question

[V8turd]

Hi all. Wondering of theres any gear ratio boffins in the house that could help me with a question as I'm not having much joy myself

So my car was a supercharged m52b28 with ZF 5 speed gearbox and 3.15 lsd.
It's now an m60 4.0 v8 with the 6 speed gearbox and the same 3.15 ratio lsd... (when I finish building it)...

For me, having had various gearbox/dif combos on different setups, the m52b28, zf box and 3.15 was perfectly geared for an e30 in my opinion. But as I've said, the v8 build is not yet complete and I haven't driven it as yet. So I dont know what it's like on the road.
So I'm trying to find out from someone who knows their salt on ratios, what will the car be like on the new setup.?
Will it be the same, longer or shorter geared??

Would really appreciate some feedback on this it would help me a lot

Many thanks

[Brianmoooore]

Depends on which 6 speed box you are using, but for the most likely, 5th gear with the new box will be exactly the same as 5th gear with the new box, leaving 6th gear as a 0.85 overdrive ratio. If you want to make 6th the same as 5th now, you'll need a diff. with a ratio of 0.85 x 3.15 = 2.68.
Changing the diff. ratio also has an effect on the lower gears, of course, and may or may not make them more suitable.

[V8turd]

That's great thanks for the response Brian.

It's the 6 speed gearbox that matches the engine, which came from an e34 540i/6

So the car will be geared the same as it was before but with extra cruising in 6th. That's probably going to work for me actually. Will see what it's like on the road then.... soon I hope

[djkostas]

If you want to make 6th the same as 5th now, you'll need a diff. with a ratio of 0.85 x 3.15 = 2.68.

Isn't it the other way around?
3.15 / 0.85 = 3.7

[Stephenmoooore]

If you want to make 6th the same as 5th now, you'll need a diff. with a ratio of 0.85 x 3.15 = 2.68.

Isn't it the other way around?
3.15 / 0.85 = 3.7

You are right. I was on the wrong side of half a bottle of red when I wrote that, and spent several minutes deciding whether it was devide or multiply. and still picked the wrong one.

[V8turd]

If you want to make 6th the same as 5th now, you'll need a diff. with a ratio of 0.85 x 3.15 = 2.68.

Isn't it the other way around?
3.15 / 0.85 = 3.7

You are right. I was on the wrong side of half a bottle of red when I wrote that, and spent several minutes deciding whether it was devide or multiply. and still picked the wrong one.

Haha , happens to the best of us mate

Thanks both