MG-Rover.org Forums banner
1 - 4 of 4 Posts

·
Registered
Joined
·
1,104 Posts
Discussion Starter · #1 ·
Ok, driving home tonight, I was cruising around 80mph (indicated) and noted the revs were at around 2500rpm (i'm dead on 90mph indicated at 3k rpm), this is a CDTi btw...and I got to thinking

I'd love a 6sp gear box. I cover a hell of a lot of motorway miles, and having something that bit quieter would be a god send. I have no reason to complain about the 330d only having 5spd as the engine is so much smoother being 6cylinder, etc.

However, my thought process lies in the following. A six speed box for the diesel would be great if you cruise at 80mph (which I think most of us do). This, if ratios were a trend, would see the engine at around 1600-1800rpm in 6th, pretty much just spooling the turbo. But if you were at 70mph in 6th, this would cause the revs to be too low to smoothly overtake and you'd have to drop a cog to get the power back, but then 90mph would be at 2krpm and would see you fly round to a fair good top speed i'd imagine (private test track permitting!!!).

I note that Quaife do a six speed FWD box for a very reasonable price (i'd effectively be getting some money back by selling my current box), but what kind of gear ratios would be needed for such an idea, and am i now taking this modification thing too far!????? Instead of dropping 800rpm off with the 6th gear, could it be a closer ratio to 5th and maybe keep it at say 2000rpm at 80 mph!?

Answers on a postcard!........what are your thoughts!? Ron, Alex, Rich!?
 

·
Registered
Joined
·
88 Posts
you would still be doing the same revs with a six speed box or a five speed box due to the final ratio being one to one,only difference is the ratio of the lower gears.
 

·
Registered
other_manufacturer
Joined
·
4,589 Posts
Just fit 19" rims and 80 series tyres.

That way you won't have any +ground clearance problems as well!!

the final drive ratios differ, so you can change the box as the top gear ratios differ as well.

Eg the diesel is .686:1 5th, diff 3.737:1. Overall 2.563:1
KV6: 0.809:1 top, 3.944:1 diff. Overall 3.19:1

So you could raise the gearing on a kv6 (and make acceleration worse) by fitting the diesel transmission.

Won't the 6 speed box off a BMW320d bolt straight on?
It should be able to handle big torque as well.

Ron
 
1 - 4 of 4 Posts
Top