1/4 mile times

[SkipB]

MDP727,

I've never really figured out what the real rear axle ratio on Backdrafts is for the stock rear end. I've been told 3:10, 3:15 and now you say 3:08. Whatever it is comes from a BMW E36 3 series from the mid 1990s. You might see if you can find a limited slip version that I think runs about a 3:45 - 3:50. There is also a limited slip you can add from Quaife to your existing rear end. I think you may be able to change ratios as well. This may speed things up a bit depending on what gear you are in and where your rpms are at the 1/4 mark. Just to confuse the issue, I have also heard you don't need a limited slip unit for the BMW rear end and that it may be faster without! In any case I would look for a numerically higher rear end ratio.

You guys that have tested various combinations (on the Backdraft only) can weigh in here and help MDP727.

Skip B

[jeffko]

I ran a 12.1 at 116 with an open 3.46. I have since switched to a 3.64 ls diff and have yet to best 12.7 at 109. The open diff was much more forgiving at the launch on radial t/a and the ls is much harder to keep a grip with.

Traction is most definitely the problem. I don't care who you are, putting 460 ft lbs of torque at the wheels with barely 1000 lbs (if that) sitting on it is next to impossible without drag radials or better yet slicks. With a set of street ets and a few practice runs I believe I could sink into the mid 11s relatively easily. Look at Chris's 60' of 1.5. That’s a mid 10 second run with a motor that has more poop. Does he have drag radials? Bet your arse he does.

I would also agree with Jerry on sitting on the rev limiter. I have intentionally done it at the last trap and I am peeking out on rpms somewhere around 100 feet before the 1/4 trap in 3rd gear meaning about 6400. You will have better times if you go ahead and shift. It takes a few tenths to do it, but running flat for 100' does not pay. The other time I do it is most assuredly unintentionally at the line. ~@~^&@!#&*$#^

Yes of course it is experience, but more than that is tires, tires, tires.

Just my two cents....


Hey Jerry, I wished I had thought to have you run my car down the track to see what it would really do.