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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > All-Wheel-Drive (Xi / xDrive) Talk > Best safe way to launch a modded manual 335XI?



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      05-31-2011, 10:14 PM   #1
skow
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2008 335XI  [4.50]
Best safe way to launch a modded manual 335XI?

I'm not much of a quarter mile runner, but I like to go on rare occasion. I'm wondering if anyone believes they have the best ~400 bhp XI (repeatable and safe) launching method that can be used a few times a year.

I currently basically launch it like i did my 320 bhp AWD mazdaspeed6; I currently rev to about 3.5k, let in the clutch over a 1/4-1/2 second (not drop it) while gassing it. This seems to work fairly well, Torque (Android app using a OBD connection) says my 0-60 is 4.5. On the Mazda, not dropping it prevented any bog-down and prevented from sheering the rear axle (was a rare but reoccurring issue for modd'ed speed6's). It was much better to take a little clutch wear than do big damage.

Am I being paranoid in not dropping?

Last edited by skow; 05-31-2011 at 11:04 PM.
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      06-22-2011, 02:37 PM   #2
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I am also interested in this.

I know several RWD 335i are launching in 2nd gear with 4000 rpm but I do not know if it is the same for a xi version...
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      06-23-2011, 04:31 PM   #3
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I just drop it around 3000rpm. Take off dtc n dsc. I've gotten my beat results like that on strip. It just squeaks for a split sec and takes off.
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      06-24-2011, 05:10 PM   #4
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"repeatable" "safe" and "a few times a year" is a tough call, because it takes practice and repetition to do solid launches safely and reapeatedly.

The safest way is to let your clutch up just short of engaging, then smoothly start putting on the gas. When rpm's are in the 1800-2200 range, smoothly start letting out the clutch and smoothly keep pushing the gas pedal to the floor. Match the speed you let out the clutch with the speed you put down the gas so that the RPM's don't drop below whatever your safe number is, like 2700 rpm. For most folks this is fairly easy to learn, and doesn't take practice. But it doesn't really "launch".


Another launch technique that takes more practice to be safe and repeatable goes like this:

1) Heel/toe the brake and gas. With the brake firmly applied, put the gas pedal down just enough to hit 3,200 rpm.

2) Smoothly let out the clutch while SLIGHTLY adding more gas as the clutch engages and the rpm's start to drop. You still aren't moving at this point. The point of this is to build boost. If you've got an accurate boost gauge, you can watch your boost gauge along with your tach to determine how fast you work your pedals.

3) Release the brake and push the gas to the floor in one motion when RPM's drop to around 2,700 rpm. At the same time, smoothly let the clutch out past the engagement point. Clutch release needs to be quick enough to chirp the tires, but not a complete dump.

This all has to happen pretty quickly. You can't sit there with the engine reving, or with the clutch slipping. How safe it is depends upon how much practice you need to do it right every time. Obviously, like everything on blogs, this is all at your own risk. Don't blame anyone if it doesn't work out well.

If you want to play with faster launch techniques, it might actually be safer for your car if you do it a couple of times a month to keep in practice, instead of a couple of times a year.

Last edited by 11Series; 06-24-2011 at 05:16 PM.
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      06-30-2011, 01:01 PM   #5
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How about some auto xi guys?

I launched mine at 2k RPMS (when I had JB+ & BMS DCI on runflats) & could not cut better than 2.0 that day.

I now have Cobb AP. I did some practicing (haven't been back to track) & launched from 2,500 RPM (Same runflats) and AP said I cut a 1.9 60'. felt like I could have stalled it up a few hundred more, but the car would not let me go beyond that point. I guess the AP doesn't tune that out.
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      10-16-2012, 09:25 AM   #6
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I heard some people do 2nd gear launch....
I haven't launch my car yet. (Saving my clutch)

Revive this thread!
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      10-16-2012, 09:35 AM   #7
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Back from the dead!

And happy to see the OP had a MPS as well, loved my Speed6. Only went through 3 sets of motor mounts before I traded it in.
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      10-16-2012, 11:12 AM   #8
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At the drag strip I've been flooring it at the first yellow and basically dropping the clutch at the third yellow, logs show that as being just under 5k rpm. On the stock clutch it doesn't grab hard enough (for me) to break anything as long as you don't get a bunch of wheelhop. My stock clutch is starting to weaken, though, and I'll need a better one before I go back to the track. I removed the CDV restriction and that helped a little, but not enough.
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