Backdraft IRS Update

BillW · #1 (**permalink**) 03-21-2009, 06:12 PM

I just installed a 3.64 LSD on my Backdraft (BMW IRS) and it was a moderate project, I did it semi-ghetto style (on my back with the car on ramps and jacks). If I was to do it again it would probably take about 3 hours, took about 4.5. I also went with an upgraded front bolt and bushing. I had a huge issue trying to remove the bushing as Jake (Metrix) forgot to include the removal bolt and I tried to use an old alternator bolt - once I had the proper one (he sent one) it was cake. Driving is very different now, the car feels a lot more powerful due to the higher (numerically) gear ratio and the LSD. You definitely have to pay attention as more power is getting to the rear and if you are not diligent, you can spin both wheels and trade the rear end for the front.
I also was able to visit Jake in LA during a recent business trip, he is a very talented guy, basically working out of a garage behind his home. Only issue is shipping, which to put it delicately, is not punctual. Overall, I would recommend him, although it may take a phone call or two. If you just want a very safe cruiser and are not interested in acceleration, then this is not for you. If you want to get every HP and ft-lbs to the pavement, then this is a must have addition.
Bill

Cashburn · #2 (**permalink**) 03-21-2009, 06:58 PM

What ratio were you running before? What transmission and engine do you have... just reference for others.

newBDR · #3 (**permalink**) 03-21-2009, 08:00 PM

is your speedo reading wrong now?

BillW · #4 (**permalink**) 03-21-2009, 09:50 PM

I had the standard 3.15 open diff that Backdraft used to supply, they now provide a 3.46 open. I have a 347 Stroker making 410 Horse and a Tremec 5 speed. The speedo is perfect, I checked it against a radar speed notification system in my neighborhood. It works off of a magnetic pickup vice gearing so that spinning part must be a constant (i.e. unchanged) when the gear is changed