I've held back from posting an early review of the product because I wanted got really get to grips with it rather than just comment that it was great and that everyone should have one.
It must be a month since the conversion was done on the car. I should add that I also upgraded the ARB's from 10mm to 25mm, fitted 19" diameter wheels with Continental conventional tyres and so on, which also have a bearing on how the car works.
I also haven't helped myself by running the car only for a couple of weeks before it was booked in with Birds. During this time I did long work journeys and didn't have a great deal of opportunity to exploit the shortcomings of the OEM setup.
To give perspective, my previous vehicle was a VW Golf IV 25th Anniversary GTI. The PD150 engine was uprated with among other things a Turbo Dynamics stage 2 turbo, larger FMIC & ali pipes, custom de-catted exhaust, Superchips custom map, KW v3 coilovers, H&R ARB's etc. To cope with 230bhp and 320lb/ft through FWD I also had a Sachs uprated clutch and Peloquin ATB differential of similar design and function to the Quaife, but specific for VAG. I understood how to get the best out of this car, did many trackdays and was comfortable chucking it down a B-road at speeds I wouldn't yet contemplate in the 130i.
However, I wanted to move on and the 130i as a package is in a different league. It provides driving pleasure on many levels and is also just a nice place to be. The modifications I decided on with Birds were first and foremost to address the shortcomings of the car (which are all to do with ride and handling) and I will be leaving the engine well alone. In my view, as has already been said, the key to this is the differential and the tyres.
In OEM form, the ride is harsh and the stiff sidewalls cause the car to bounce and lose grip. This then unsettles the rear and the open diff allows a wheel to spin up. Then the DTC steps in and even during innocuous manoevres the light is flashing away on the dash. I didn't really drive the car hard in damp or wet conditions before having the modifications so will have to take other peoples' word for quite how magnified this gets in slippery conditions.
With the Quaife diff (coupled with the tyres which in themselves also make a massive contribution to improving ride and handling) the DTC can be left fully on and in normal driving it just won't intervene. So the difference is that obvious.
When I make a conscious decision to get the hammer down, I semi-disengage DTC with a single push. Again, I haven't put the car through its paces in a variety of conditions but I have held the car in controlled slides around and out of dry roundabouts. Really you have to want to show off though, it is very hard to unstick; grip levels are so high. My best test was letting a client who is a Subaru dealer and experienced historic racer stuff it down his favourite B-road. He was very impressed indeed and it will be a while (if ever) before I contemplate the speeds he attacked this twisty bit of tarmac at; the car took everything he threw at it.
So, this is my feedback so far. No trackdays yet and certainly no autocross, but I'm very happy with the diff and pleased I decided to get it done so early in my ownership of the car.
If you want to see what one of these will do in the right hands, check out Chris Harris driving Birds' 335i demonstrator with 380bhp and the Quaife;
mms://ms.groovygecko.net/groovyg/cl...r/chrisharris/mar_07/Hartge3series_512kws.wmv