CaptainK
CCCUK Member
Hello, after my recent long-ish drive to the BMS, it got me thinking again about RPMs and overdrive gearboxes. Its a long term thought of mine to put a 5 speed into my C3. I did originally think 6 speed, but I see its more hassle putting one in. I'm happy with my current 1-4 gearing, just want an O/D gear.
I was wondering if anyone here has a 5 speed in their C3 and could tell me your rear diff ratios, your 5th gear ratio, and what differences in RPM did the 5 speed make for you at a given speed?
My C3 currently has a 3.08 LSD rear diff and is a 4 speed manual. So in 4th its 1:1. I do around 2.7k rpm in 4th at 70mph (I say "around" 2.7k rpm as my speedo is inaccurate, so not entirely sure its 70mph), but looking at RPM calculators online adding in my tyre size and rear diff it seems about right.
I'd be really interested to know what my RPM would be with a 5 speed. I've seen online there are 0.81, 0.72 and 0.68 O/D options for 5 speeds. I'd probably want the 0.68 for maximum lower revs, but the other gear ratios I'd want for better acceleration. I have put those into online RPM calculators, but I'm not sure how I work out the "complete drivetrain ratio" for the 5th speed - for the 4 speed the gearbox is 1:1, so my drivetrain is just the rear diff ratio of 3.08. So with a 0.68 5th gear, would my "complete drivetrain" be 3.08 + 0.68 = 3.76, or 3.08 - 0.68 = 2.40 or something else? I'd assume the 2.40, in which case my revs at 70mph should drop from around 2.7k to around 2.1k rpm.
Anyway, be interested to hear results from people that have done the conversion.
I was wondering if anyone here has a 5 speed in their C3 and could tell me your rear diff ratios, your 5th gear ratio, and what differences in RPM did the 5 speed make for you at a given speed?
My C3 currently has a 3.08 LSD rear diff and is a 4 speed manual. So in 4th its 1:1. I do around 2.7k rpm in 4th at 70mph (I say "around" 2.7k rpm as my speedo is inaccurate, so not entirely sure its 70mph), but looking at RPM calculators online adding in my tyre size and rear diff it seems about right.
I'd be really interested to know what my RPM would be with a 5 speed. I've seen online there are 0.81, 0.72 and 0.68 O/D options for 5 speeds. I'd probably want the 0.68 for maximum lower revs, but the other gear ratios I'd want for better acceleration. I have put those into online RPM calculators, but I'm not sure how I work out the "complete drivetrain ratio" for the 5th speed - for the 4 speed the gearbox is 1:1, so my drivetrain is just the rear diff ratio of 3.08. So with a 0.68 5th gear, would my "complete drivetrain" be 3.08 + 0.68 = 3.76, or 3.08 - 0.68 = 2.40 or something else? I'd assume the 2.40, in which case my revs at 70mph should drop from around 2.7k to around 2.1k rpm.
Anyway, be interested to hear results from people that have done the conversion.