Gear and diff ratios

[Richard]

In my planning I've been considering potential future power upgrades and ratios for Diffs.

Because of the relatively low weight compared to road cars and stiffness of the chassis an LSD makes sense from the start if possible, views / opinions welcomed.

Then there is the ratio given power to weight ratio being pretty good before engine upgrades and changes may make gearbox ratios a bit of a mute point, I'm not thinking of tuning for various tracks or in that detail but if I have choices now I'd like to put some good building blocks in place.

An aluminium flywheel has obvious uses in these light weight cars but a real cost detriment.

Opinions / observations please ?

['The Gaffer']

Hi Richard, sorry I'm no technical expert but I'm hoping in time we we get a few tech heads join up.

I did do a little research a while back regarding diff ratios just out of interest, and found these codes to id a Ford diff. Maybe this will help a bit...

Differential And Axle Codes
The following list of codes help in finding the right ratio:
Ford axle codes(on the VIN plate): A=3.36 B=3.77 D=3.92 F=3.842 J=4.056 K=3.31 M=3.14 N=4.29 P=3.58 J=3.62 V=3.33 Z=3.59 2=4.27 3=3.62 4=3.82 5=3.26 6=3.12 8=3.56

3,14 CW47-Pin15
3,38 CW44-Pin13
3,62 CW47-Pin13
3,92 CW51-Pin13

3,77 CW49-Pin13 6.5 inch diff

3,38 fitted to 1,6 OHC ECO 5 speed
3,38 fitted to 2,0 OHC HC
3,38 fitted to 2.3 v6 ESTATE
3,14 fitted to 1,6 OHC ECO 4 speed
3,14 fitted to 2.3 v6 SALOON
3.14 fitted to 2.3 Diesel

85GG 4006 DC --- 3.97
85GG 4006 BC --- 3.62
85GG 4006 AC --- 3.38
85GG 4006 FB --- 3.36
87BG 4006 GB --- 3.14

86GG 4006 AAA --- 3.92 LSD
V87BB 4006 BAA --- 3.62 LSD
V87BG 4006 CAA --- 3.38 LSD
85GG 4006 AAA --- 3.36 LSD

Vin plate codes for Diff ratio:

Ratio Code
3.14 M
3.36 A
3.38 U
3.62 V
3.64 3
3.92 D

[Richard]

Thanks, going to prove useful to a few folks over time.

Has anyone got thoughts on the better combination of ratios on the assumption the bits all fit ?

['The Gaffer']

My LSD diff ratio of 3.62 to 1 was based on a Fireblade bike engine. So much depends on power and torque of engine to get it just right.

[Richard]

What I've found so far is that LSD is pretty much the sensible thing (that won't read well without context), but not essential.

All the ratios from road cars kind of go out the window a bit given the weight difference and the effect on acceleration.

If in searching I find some explanation other than gears to speed I'll drop the link in.

[Richard]

Here is one useful link I have for gear ratios etc.


http://www.unixnerd.demon.co.uk/revs.html

['The Gaffer']

Have you definatly decided on an engine? If so I would have a word with the supplier about the gear ratios it comes with. You can then decide what diff ratio you need?.

[David H]

Depends on weight, use intended, bike or car power etc etc. My advice would be to talk to gearbox specialists as there are an infinite no. of set ups. For example, If your going Ford power talk to BGH for type 9 boxes and ratios. They will do the calcs for you. Gearbox ratios make the world of difference to the drive.

careful on lightening flywheels. My car is quite light and a flywheel thats too light would make the inertia on take off different meaning i would have to work harder. Stalling is easier. Its not as smooth a ride. If your on track more then lighten away cos its quicker etc

what are you building?

dave

[Richard]

Depends on weight, use intended, bike or car power etc etc. My advice would be to talk to gearbox specialists as there are an infinite no. of set ups. For example, If your going Ford power talk to BGH for type 9 boxes and ratios. They will do the calcs for you. Gearbox ratios make the world of difference to the drive.

careful on lightening flywheels. My car is quite light and a flywheel thats too light would make the inertia on take off different meaning i would have to work harder. Stalling is easier. Its not as smooth a ride. If your on track more then lighten away cos its quicker etc

what are you building?

dave

Building GKD Legend based on BMW E36 4 cyl engine. This is where there are enormous numbers of options but little information with it in very lightweight vehicles.
For example my donor car has a dual-mass fly at 25.8lbs, makes it very smooth of course but that is heavy.
Then the mixture of standard gearbox  to diff is quite high but the diff came in two sizes and I think only the smaller one fits, not sure yet and can't use the M3 from that era as not a 4 cyl engine and rear track was bigger.

What I've been trying to find is some rules of thumb for the mixture of ratios but have yet to do so, I think first version may have to be very stock and then perhaps change some things, can't decide at the moment.

[Richard]

Found one of the handy links to work out speed at various rpm from knowing your ratios, it may be of use, especially if you want to keep that extra gear change out of 0-60/100 times.

http://www.kabamus.com/garage/gears.html

[David H]

And so it begins........ Frothing at the mouth till 3am on the internet researching a ratio or a nut in stainless.... sounds familiar. Take away food until the project is finished!!