[tscdennab]

Introduction

After participating at a legal drag racing event which took place on a closed road and seeing how much traction problems I had, I decided to invest my mod savings into a limited slip differential in the hope that I will improve my 60ft times in drag racing competitions. We don't have dedicated and "prepped" drag strips here, our legal events take place either on closed streets or old unused airports.

The decision based on research

Being located in Europe basically I had two options: Quaife or Drexler. These are two different designs, Quaife is a Torsen (gear type) differential, while Drexler is a clutch-type differential. In my research, I kept reading that Quaife is better for the street with no audible noises and no maintenance, while Drexler is better for racing with some maintenance like changing clutches at 75.000kms and changing oil more often. Also torsen-type differentials are very popular on front wheel-drive cars, the new Focus RS has a Quaife LSD.

I also read that clutch-type differentials begin their locking action faster than Torsens, which means a bit of advantage in drag racing. I read some reports (not few) about torsen-type differentials having a tendency to break when sudden torque is applied, such as drag racing. But I only read about one Quaife failure, however. Also, Torsens do not work if one wheel has no traction at all (like on some racetracks or on ice).

Since most racing cars use clutch-type LSDs (Drexler in particular is used by BMW Motorsport and even in some Alpina cars like the B3 S), I decided to bite the bullet and get the best LSD out there (in my research) which is the Drexler clutch-type differential.

Technical information about the Drexler differential

The Drexler differential that I chose is a 2-way differential (it works both on acceleration and braking), with ramp angles of 50 degrees/40 degrees on acceleration/braking side and a 50Nm preload. The ramp angles chosen lead to a locking percentage of 40% on acceleration and 60% on deceleration, which is what Drexler recommended for a sporty car that can be safely driven on the street. Keep in mind that when LSDs were available as option in BMW cars, the locking percentage was 25%. Porsche GT cars have a locking percentage of 40%, as far as I read.

Oh, and the Drexler weights 11kg, while my old open diff weighted 6kg. The entire rear axle drive weights 35kg with the standard open diff and 40kg with the Drexler differential.

Pricing

I managed to obtain a price of 2025EUR excluding VAT. The price includes everything but dismounting and mouting the rear axle: they unweld the ring pinion from the old open diff (I have a welded ring) and convert it to bolted pinion, they install the LSD into the rear axle, and then they deliver the completed rear axle to me. I just have to put in their recommended Castrol SAF-XJ 75w-140 oil (now superseded by Castrol Syntrax Limited Slip 75w-140) and that's it. The rear axle dismounting-mounting cost me 100EUR at a local shop.

I had to remove the rear axle from my car and send it to Drexler, which led to exactly 2 weeks of downtime.

Driving Impressions:

Unfortunately I didn't have time to test is much until now, but I did notice some important things:

First and most important to me, there is no sign that anything was changed on the car. No strange noises (even when parking), no vibrations, basically you don't know it's there.

But when you take the first corner and accelerate, you notice that the car accelerates like you would want it to accelerate, instead of losing all the power due to wheel spin.

Also in straight line the car doesn't go sideways like usual but always seems to go in a straight line. Traction control does intervene though if you lose traction.

I will post more impressions as I will test it more. There is a strong possibility that I will attend a drag racing contest this weekend, I will update my impressions after that.

Driving impressions Update:

Today I had the chance to test the Drexler LSD on some twisty hills. At the end, I really needed some motions sickness pills. The car pulls so hard out of corners like you wouldn't believe ! I really don't think I can take more lateral acceleration than this

When exiting corners hard, the exit is very "clean" with no unwanted fishtailing. The LSD transitions are very smooth, I can't feel them. If the traction is good, the car just pulls straight out of the corner like it is on rails. If the traction surface is not very good, you get some drifting but very natural and correctable.

However, I did try to accelerate hard on a wet section of the road (Nitto 555R rear tires), with DTC on (DTC button pressed once). The car goes sideways, and if you let off the throttle, it comes back in line but it does so more violently than with the open diff. I don't think it's a good idea to do this on snow or at higher speeds. Like everyone recommends, it's not a good idea to suddenly let off the throttle with an LSD. However it's not nearly as bad as I read in other reviews.

I feel that my car is now "complete". Without the LSD there were numerous occasions when the car seemed underpowered, but now I don't get this feeling anymore.

Conclusion:

I am very happy with my modification but the LSD is not something to blow you away like you read in other reviews. However, the car now behaves like it should and doesn't feel like it has half the power in some key scenarios.
If you want a LSD I think you should go the cheapest route that you can find, but do choose a trusted brand like Drexler, Quaife, Wavetrac or OS Giken.