Torsen LSD

Technical Area Forced Induction & ITB
2

Afternoon All,

I’m trying to navigate the minefield that is Diff Ratios in readiness for having my 1995 1.8 NA Turbocharged. I want to replace the standard open diff (4.1:1 - I think) with a Torsen LSD that has a taller final drive to better suit the extra power of the motor and make motorway cruising more comfortable.

I’ve read that the BBR Anniversary Mk1 Turbo can be spec’d with LSD and ‘final drive from a 6 speed mk2 model’. I presumed that this is a 3.909:1 Torsen Diff from a 6 speed NB anniversary model ?

However, I have seen advertised a ‘Type 2 Torsen 3.6 ratio NOT fuji LSD’

Questions:

Is this ratio correct - was there ever an LSD with this ratio or was it only an open diff on the 6 speed 1.8 NB (3.636) ? 

Would it be better suited to a 220BHP Turbo than say a 3.909 or 4.1 ?

If it is the genuine article will my exisitng driveshafts fit ?

What difference is there between the Torsen and Torsen Type 2 ?

Is there a way to determine the final drive ratio by looking externally at the casing for a serial number or something or do you just have to take the vendors word ?

Finally, what have other people fitted - would a 4.1:1 LSD be OK ?

Thanks in advance

Roo

3

To determine the ratio of any dif do you not just jack the car up and turn the wheels, then count the number of turns the prop has done?

4

Thanks Paul but I was thinking of the scenario whereby the diff has been removed from the car and is advertised for sale. Short of removing the cover and counting the teeth on CWP is there an external stamp that identifies the ratio ?

5

Have a play with this handy diff ratio guide:

 

https://www.flyinmiata.com/tech/gearing.php

 

You can kinda work out what you already have using this. Just note what RPM your engine is running at certain speeds. E.g. 60 and 70 mph.

 

 

6

Thanks for the link to the excellent FM site which is very useful.

I’ve found out that it is the mk2 VVT 6 speed that does indeed have a Torsen Diff with a 3.6:1 ratio. On the FM site it shows that if I fitted one of these then it will drop the revs in 5th by circa 400rpm @ 80mph over the standard 4.1 diff. So whilst not a huge difference, if I’m going to fit an LSD as part of my Turbo project then I may as well be one with this ratio. I’ll let you know how I get on !

Thanks

7

You’re probably wanting the torsen brand lsd from an early mk2.5 sport, these have the ratio you want, around 2003 the car was revised slightly to use the tochigi-fuji super-lsd instead, same ratio but a different internal mechanism (some say weaker)