Diff Ratios

[Steve T]

Hi

 

What was the 'normal' open diff ratio fitted to Roadsport SV's 1.8 in 2006, was it 3.62 or 3.92, is it stamped on the casing somehwere ?

 

Next question, when having an LSD/ATB fitted to the same diff, I presume the drive ratio will remain the same as the open diff ration assuming the crown and pinion are reused and decide the ratios ?

 

I am just going throught the LSD conversion process and wondered why the ATB listed on the CC parts site shows a ratio of 3.38, why would it be different and does it matter/change performance (I assume it will increase Torque and reduce top speed a bit when swapped from an open 3.62/3.92 open).

[Stationary M25 Traveller]

In my CC handbook it says:-

 

Classic 3.89:1

Roadsport 3.92:1

Superlight 3.62:1

[Shaun_E]

It is usual for a 5 speed car to have a 3.92 and a 6 speed car to have a 3.62 but of course the specification could be changed by the buyer or a subsequent owner.

You are correct in that, when having an LSD fitted, the crown wheel and pinion are reused and the ratio stays the same although it is a good opportunity to change if you wanted to. A 3.92 with 6 speed provides better acceleration but obviously reduces top speed and increases cruising RPM. A lot of sprinters go this route as I have.

The 3.38 is, I think, normally fitted to the CSR and would be a bit tall for a Roadsport - acceleration would be poor.

[Steve T]

So assuming I have a 3.92 and I change the innards for an ATB and keep the 3.92 ration, I would notice no difference appart from the increased traction benefits of the ATB ?

[Dignity]

Steve,

There should be a metal tag on one of the upper casing bolts that will tell you the ratio.

Mine was 3.92. Supersport/6speed

Rgds

Dignity

[Steve T]

Great thanks, I will take a look.

[Shaun_E]

Quoting Steve T: 

So assuming I have a 3.92 and I change the innards for an ATB and keep the 3.92 ration, I would notice no difference appart from the increased traction benefits of the ATB ?

Correct