7 replies to this topic

[diogoteix]

Hello!

I'd like to reduce the final drive ratio of my Mini from 3.44 (62/18) to something around 2.9 to 3.1 (original ratio of my 1992 Cooper Spi by the way), since I significantly increased the engine HP and would rather cruise below 5500rpm on the highway (speed controls are not that anoying in Portugal )...

My 1st question is:
- can I keep the 62 teeth crownwheel and just change the pinion to a new one with 20 (62/20=3.1) or 21 teeth (62/21=2.95) ? Will the space between the teeth "fit" or will the crownweel and pinion just "eat" each other?
- or do I a need to change the crownwheel as well, in order to have a "matching set" to have the correct teeth spacing?

My 2nd question is:
- the minimum ratio offered by the semi-helical crownwheel / pinion kits on Minisport is 3.93 (3.44 for LSD type).
- is there a way, with this type of semi-helical crownwheel, to still get a decent final drive ratio, so that you can cruise at 5000/5500 rpm for 100mph by changing drop gears or gearbox ratios?

Thanks for your answers!!!

Diogo

[icklemini]

My 1st question is:
- can I keep the 62 teeth crownwheel and just change the pinion to a new one with 20 (62/20=3.1) or 21 teeth (62/21=2.95) ? Will the space between the teeth "fit" or will the crownweel and pinion just "eat" each other?
- or do I a need to change the crownwheel as well, in order to have a "matching set" to have the correct teeth spacing?

no
The crownwheel and pinions must be a matched pair:

Ratio, pinion, crown wheel
4.333 15 65
3.938 16 63
3.647 17 62
3.765 17 64
3.444 18 62
3.105 19 59
3.211 19 61
2.950 20 59
2.762 21 58

My 2nd question is:
- the minimum ratio offered by the semi-helical crownwheel / pinion kits on Minisport is 3.93 (3.44 for LSD type).
- is there a way, with this type of semi-helical crownwheel, to still get a decent final drive ratio, so that you can cruise at 5000/5500 rpm for 100mph by changing drop gears or gearbox ratios?

Well you wont get far by changing the gearbox ratios... as the top gear is 1:1 anyway..

Drop gears alter the ratios across all the gears:
but you wont get a 3.93 anywhere near a 2.9 or a 3.1 just by changing the drop gears

Edited by icklemini, 24 September 2010 - 05:10 PM.

[Guess-Works.com]

1. No you can't...

2. Don't restrict yourself to looking at minisport...
but to achieve 100 @ 5-5.5k you'll need an FD around 3.1

Edited by Guess-Works.com, 24 September 2010 - 05:08 PM.

[diogoteix]

My 1st question is:
- can I keep the 62 teeth crownwheel and just change the pinion to a new one with 20 (62/20=3.1) or 21 teeth (62/21=2.95) ? Will the space between the teeth "fit" or will the crownweel and pinion just "eat" each other?
- or do I a need to change the crownwheel as well, in order to have a "matching set" to have the correct teeth spacing?

no
The crownwheel and pinions must be a matched pair:

Ratio, pinion, crown wheel
4.333 15 65
3.938 16 63
3.647 17 62
3.765 17 64
3.444 18 62
3.105 19 59
3.211 19 61
2.950 20 59
2.762 21 58

My 2nd question is:
- the minimum ratio offered by the semi-helical crownwheel / pinion kits on Minisport is 3.93 (3.44 for LSD type).
- is there a way, with this type of semi-helical crownwheel, to still get a decent final drive ratio, so that you can cruise at 5000/5500 rpm for 100mph by changing drop gears or gearbox ratios?

Well you wont get far by changing the gearbox ratios... as the top gear is 1:1 anyway..

Sorry !!! I knew I knew it !!!


Drop gears alter the ratios across all the gears:
but you wont get a 3.93 anywhere near a 2.9 or a 3.1 just by changing the drop gears

Do you know of anyone selling a straight cut or semi-helical crownwheel / pinions with a 3.1 ratio ?

[diogoteix]

My 1st question is:
- can I keep the 62 teeth crownwheel and just change the pinion to a new one with 20 (62/20=3.1) or 21 teeth (62/21=2.95) ? Will the space between the teeth "fit" or will the crownweel and pinion just "eat" each other?
- or do I a need to change the crownwheel as well, in order to have a "matching set" to have the correct teeth spacing?

no
The crownwheel and pinions must be a matched pair:

Ratio, pinion, crown wheel
4.333 15 65
3.938 16 63
3.647 17 62
3.765 17 64
3.444 18 62
3.105 19 59
3.211 19 61
2.950 20 59
2.762 21 58

My 2nd question is:
- the minimum ratio offered by the semi-helical crownwheel / pinion kits on Minisport is 3.93 (3.44 for LSD type).
- is there a way, with this type of semi-helical crownwheel, to still get a decent final drive ratio, so that you can cruise at 5000/5500 rpm for 100mph by changing drop gears or gearbox ratios?

Well you wont get far by changing the gearbox ratios... as the top gear is 1:1 anyway..

Sorry !!! I knew I knew it !!!

Drop gears alter the ratios across all the gears:
but you wont get a 3.93 anywhere near a 2.9 or a 3.1 just by changing the drop gears

Do you know of anyone selling a straight cut or semi-helical crownwheel / pinions with a 3.1 ratio ?

[diogoteix]

1. No you can't...

2. Don't restrict yourself to looking at minisport...
but to achieve 100 @ 5-5.5k you'll need an FD around 3.1

Thanks, do you have seen someone selling a SC or semihelical crownwheel / pinion set with a FD of 3.1??
I'm looking around but for the moment nothing came out...

[Guess-Works.com]

Quite simply no, I've not seen anything SC or Semihelical < 3.4, and to be frank, not a lot of point, a std Helical should be up to the job... SC and SH are generally reserved for competition use, and if you are in a competition environment, you'll probably want to be doing many many more RPM @ 100... therefore shorter final drive..

I can get hold of 3.4 SC final drive to fit a standard diff ( ie not LSD )

Edited by Guess-Works.com, 24 September 2010 - 06:18 PM.

[diogoteix]

Quite simply no, I've not seen anything SC or Semihelical < 3.4, and to be frank, not a lot of point, a std Helical should be up to the job... SC and SH are generally reserved for competition use, and if you are in a competition environment, you'll probably want to be doing many many more RPM @ 100... therefore shorter final drive..

I can get hold of 3.4 SC final drive to fit a standard diff ( ie not LSD )

Thanks for all your anwers, I'll have a thinking to all this feedback!