Launch Tips for Drag Racing- 1/4 mile

[SilverStreak]

Now to your questions:

"I just get lost here.. "stab back down...... 2/3rd stab then squeeze..." ??? uhhhh uhhh?? "

Throttle stab = slamming the throttle back to a certain % of the way to the floor. Like flooring the accelerator, just not all the way down to the floor.

Then squeeze it the rest of the way to the floor, quickly but gradually.

All of this is designed for one thing- for maximum acceleration. And for maximum acceleration, you need to be on the very brink of wheelspin, without actually spinning wheels and losing traction.

Now, this is gonna differ from car to car, day to day, track to track, so it takes tons (and I mean TONS) of practice to get a feel for how much is too much, and how much is not enough.

My car makes 321 rwhp, maybe even more, and only weighs about 2700 lbs without me in it, so I have a traction problem. Your car may not. You may be able to floor it on every shift and not even get more than a chirp. So the throttle stab technique may not be needed for you.

For me, I get sideways on the 3-4 shift at 93 mph on a prepped track surface with drag radials...

"and t hat last paragraph.. kinda worded confusingly.. so.. if we feel like we're saving some of the clutch we're doing it right?"

No, complete opposite. If you feel like you went even the least bit easy on your clutch at launch- you're not doing it right.

If you cringe, feel like you've totally abused your clutch, feel guilty afterwards, feel like you're gonna need to replace it later that afternoon- you're doing it right....

(Please understand, there's some sarcasm in those comments for the sake fo humor).

"and... oh.. are we doing the "clutch riding" thing for every shift or just the initial launch and pop the clutch for the remain shifts?!? .. wasn't quite sure on that"

You only do it as you need it. You may not even need it at launch, some don't. You do it only when it's required to remain at the very brink of wheelspin, without actually breaking traction.

[D_ALPINE_M]

Very nice post Dave. I will give it a try when my car is back in order.

[KAMIKADZE]

Hey Dave - it is super duper post
I can't imagine that 320rwhp car can enter in 11 sec zone but you can .
Please tell me - if a car do 13 sec flat when starting from 1500rpm with no wheel spin what can be the time launching from 4500 on street and 5500 on drs again no wheel spin ?

[SilverStreak]

thanks for the kind words. 321 rwhp in a car that weighs about 2700 lbs without a driver, can do a lot if it has traction.

as for your question, i'm unclear as to what it is you're asking. can you explain further what it is you're asking?

[KAMIKADZE]

I see that your 60' is 1.648 - If it is at perfect launch at 5500 what will be your time if launch at 1500rpm and what 1/4mile time

[SilverStreak]

oh i see, i have no idea. optimal launch is as high in the rpm range as traction will allow for you to launch, so that when it grabs, the tach dips to torque, as as close to it as you can get (as tractions allows, etc...)

i know on my stock 245/40-17 dunlops on the street, depending on conditions i can only launch at 3500-4500 rpms sometimes. but when i went to the track, where it was measured, i always had my drag radials on, so i could launch and optimize my traction, etc.

i really would not be able to even guestimate what you're asking, launching at 1500 rpms, what that would produce in terms of 60' times, and 1/4 mile et's....

[MillertimeM3]

Is it really bad for the clutch to launch that high though?

[SilverStreak]

Originally posted by MillertimeM3
Is it really bad for the clutch to launch that high though?

what's bad for the clutch is launching properly for optimal launch. whether you rev and hold steady at 2500 rpms or 5000 rpms, it's not great for the clutch.

launching properly is not good for the clutch. but as a drag racer, the clutch is like brake pads or tires, they're made to wear out.

at the auto-x, you will wear out your brakes and tires pretty quick. at the drag strip, it's your clutch that takes the beating...

[MillertimeM3]

10-4 roger that

[SilverStreak]

...so go beat your clutch and have some fun!

[SilverStreak]

Some new Q&A with some folks that might prove helpful to others:

"Hello SilverStreak,

I was wondering if you could give me some advice regarding launching my car.

Setup: E36/328iC with JC cams, etc., good for 202 whp at 70+F / 4300 ft. 225/40 18'' S03. UUC Stage II lightweight Flywheel & M5 clutch.

I have never experienced any kind of wheelspin besides doing a U-turn in first gear WOT. I don't think that just dropping the clutch is a good way to launch a car.

Although today it is just around 35F in SLC I couldn't wait any longer to drive my convertible after the winter break.

The engine should gain a couple of horses and the tires should have less grip because of the low temperature. I launched at around 5,800 RPM (redline for me is 6,900) with no wheelspin and just some slippage of the clutch.

My question is: Should I reduce the launch RPMs to avoid the clutch slippage? I'm not sure what to change in order to gain better acceleration.

In a couple of months, my car will 'some new mods'. Then I obviously have to change my launch again. I expect major wheelspin and clutch slippage. Any advice on how to modulate between those two, e.g. minimizing wheelspin I would guess.

However, if I already experience clutch slippage in my current setup with no wheelspin, should I try to engage the clutch fully as soon as possible and then modulate the wheelspin with the throttle?

I know you recommend doing the modulation mostly with the clutch keeping the RPMs constant, e.g. around 5,000RPMs. I just have a hard time seeing that work when my current M5-clutch (less than 4,000 miles with less than 20-30 launches) is already slipping with just 202 whp but the tires show no spin at all.

I would appreciate your advice."





Actually, I never recommend anything steady for any car, cuz they are all different. In your case, you're getting good traction now. That's good.

But the key with modulation to maximize your launch is to push it to the point, the very brink of wheelspin. I don't know where your torque peak is with your mods, but take a peek at your dyno sheet if you have one.

Practice, and watch where your tach falls when the tires grip at launch. You want the tach near torque peak when you launch- when the tires grab, etc.

So if you can launch at whatever rpm you can, without wheelspin, so that the tach drops no lower than your car's torque peak.

Now, if you can launch at that magical rpm without wheelspin, you won't need to ride the clutch as much at launch- that's good. From there, you want to launch as quickly as you can without breaking traction.

I never recommend clutch drops, horrible for the car, the diff, the tranny, etc.... But if your car does not have a traction problem, and you're at the very edge of wheelspin occurring, from there, you want to work on how quickly you can launch, coordinating the pedals for the quickest take off.

It's kinda hard to put into words, but if that didn't make complete sense, let me know, ask some more questions, and I'll try to explain further.

Dave




"Hi Dave,

Thanks for your quick response. My wtq is 182 @ 4,950 but I already get 180 ft/lbs @ 4,400.

What I read in your response is: keep the RPMs at maximum torque. If you have no spin or slippage, reduce the time to fully engage the clutch.

Well, what do I do about the clutch slippage that I have? Should I reduce the torque (lower RPMs) to the point that there is no clutch slippage or should I just wait for the clutch to grip keeping maximum torque?

Also, when I eventually experience both, wheelspin and clutch slippage, how should I negotiate between those two? Would you reduce torque by using lower RPMs and minimizing riding the clutch (being easier on your car) or would you keep the engine at maximum torque and modulate with the clutch the amount of torque that you send to the wheels?

I guess if you are riding the clutch you can easier modulate to the traction that you get (which may be very different form launch to launch) but the clutch has to suffer a bit more.

Or you choose lower RPMs, being easier on the clutch but loosing the chance on taking advantage of "finding" more traction in a new launch.

The more you think about it the more variables go into the equation I think.

Thanks for taking the time getting my thoughts straight."



What I would do is keep the tach at max torque for launch. Meaning, I would not lower rpms no matter what. If your torque peak is 4400-4950, you make sure that when the tires grab and the clutch comes out that your tach falls no further than that range.

As you dial that in, if you can find a way to have the tach fall no further than 4950 rpms, all the better. So I'd sit there, staging, with the clutch part way out on the brink of grabbing, revving it up to whatever rpm makes sense, keeping it steady.

The light goes green, the gas pedal goes down very quickly, the clutch comes up as quickly (don't pop it, though- that's hard on the drivetrain).

As the tires dig and launch, ideally you want the tach to fall back to 4950 rpms, and to do so with no wheelspin. From there, once that's mastered, it's a matter of how quickly you get the gas down, get the clutch out and get moving forward.

For practice's sake, I wouldn't worry about R/T's for a while, just work on your 60' times.

If you find that each time you can hold her steady at (say for the sake of example only) at 5800 rpms and that each time you launch the tach drops back to 4950 rpms and you can launch with no wheelspin-- that should provide you with the quickest/best launch possible for your car.

If, given that scenario, wheelspin is not an issue for you, God bless you my son, and go with the grace of God...

If you want anything to take the abuse of a hard launch, you want it to be the clutch. Letting the clutch take the abuse saves your diff, driveshaft, tranny, etc... from taking the brunt of it. Yes, a proper launch will beat the clutch a bit (just sitting there staging holding it at a steady rpm with the clutch on the brink of grabbing will amount to some abuse- and you haven't even launched yet at that point)- but that's the point-- clutches were made to wear out, differentials and trannies weren't...

Make sense?

Dave





"Hi Dave,

That makes all a lot of sense. Just one last question: When I have the clutch pedal completely released there is still some slippage of the clutch for a second or two.

Anything I should do differently besides getting a stronger clutch?"



If the clutch is fully engaged, and it still slips a bit, even just a little, it's getting to be about time for a new clutch. If drag racing is to become part of your regular regimen, a stronger one for sure.

Dave

[MillertimeM3]

just make sure you dont have a cdv valve or you will just screw your car up! I did!

[SilverStreak]

cdv valve?

[MillertimeM3]

You're probably talking about the CDV (Cluth Delay Valve). There's an ongoing discussion about it on M3Forum.com. First, the M3 cars should not have a CDV. There have been reports of early-year model E46 M3's that have one, either intentionally or by manufacturing errors. Without a CDV, you should be able to power-shift without any problem. Second, yes, you can have it removed. In fact, I am going to see a BMW shop today to check if my car has a CDV. (I doubt it by the way I can shift, but I want to double-check.)

FYI, all non-M cars with a manual transmission now have a CDV.

Hope this helps.

I asked the same question..haha this is what I found out....

[SilverStreak]

Is it part of the newer throttle by wire systems?

[MillertimeM3]

its a hydrolic clutch pump or somethin.....

[SilverStreak]

Thanks... I think...

[black_box]

courtesy of UUC motorwerks:
http://www.uucmotorwerks.com/html_te...heck_valve.htm

[SilverStreak]

Thank you!

[megatron]

thanks for this advice silverstreak. i'm doing my first scca pro solo this weekend, which is basically a drag race with turns.
http://www.scca.org/amateur/solo2/prosolo/

i've been to a real dragstrip just one pass, so hopefully i can take these tips to heart and get some good results. i'll let you know.

[SilverStreak]

Good luck, man! You can practice these tips on launching in a deserted parking lot or back road, just practice the launch over and over again, get the feel, etc...

[CSBM5]

Dave,

Here's a better link along with a great guy (a Dave also ) with a great solution to the CDV issue! I posted this here as I think it is relevant to any of the BMWs shown in the list (on the link) if they are going to be taken to the strip.

Dave Zeckhausen's CDV information


Chuck

[SilverStreak]

Thanks a lot, Chuck!

[Calcartman]

Awesome Post(s).

I will be going drag racing for the second time ever on wednesday and i need to go practice my launching. I have never been to a dyno with this car (completely stock 97 e36 m3), and im wondering if anybody could give me and estimate as to where my peak torque might be.

last time i was there i was launching at 3500-4500 and i had very mixed results. The first time i think was at 3500, i had a 2.2 60' and ran a 14.898 @ 91.83. The second time i forgot to turn ASC off and it bucked the car and halted me for a second. The third time it was about 10 degrees colder out and i launched at about 4200 i think and i spun the tires ~30' down the track.

im guessing peak torque is in the 4000 rpm area, but i dont have a clue. so any help would be great.

Oh, and if anybody goes to Sears Point (infineon) raceway on wednesdays and sees an estoril e36 m3 sedan; its me.

[SilverStreak]

If traction is an issue, don't worry so much about torque peak just yet, just launch as high as you can without wheelspin.

Good luck! Post your results in a new thread below in the forum.