Launch Tips for Drag Racing- 1/4 mile

[SilverStreak]

Time and experience, and lots of practice- there truly is no substitute when it comes to drag racing, and the launch... You're getting there, Ron, I expect to see you in the 13's this season...

[jesd325is]

hey dave:
how much of a part does altitude have with 1/4 mile times. i am planning on hitting the track just for fun (i don't expect miracles), and to see if the cam upgrade (next week) helps a lot or a little with my times. i am going to check a topographical map of the tracks location to see where it stands.

[knudsonm]

Air quality plays a big part in performance. Heat and elevation are the enemies of an internal combustion engine.

[jesd325is]

i was checking eleveation maps (topographical) and the track is about tthe 4000ft zone. is that too ridiculously high? i am heading off in a while. i have a sub system in the trunk but i want to run it how i would every normal day for a bit then may do some weight reduction towards the end of the day :
the only prep i may do is psi changes in the tires

[SilverStreak]

Air density (which involves elevation, heat, humidity, etc) plays a huge factor in ETs and traps. 4000 ft is huge...

[SilverStreak]

A good question about traction and clutch use:

"theWoodside wrote on 03-18-2003 02:25 AM:
hey dave i just wanted to ask a quick question. i dont know if u remember but i said at the top of first i was coming off the clutch too quickly cause i thought i was in the clear and i was getting wheel hop towards the end of 1st. now say mid way through 1st i started to spin or got wheel hop. would u moderate it out with the clutch or gas. im still not sure if you would just back off giving it more throttle or get it back in check with the clutch. "



Response:

"Definitely use the clutch to moderate the power to the ground, no matter where you are: at launch, halfway thru 1st, top of 2nd, etc.

I often find myself not even getting the clutch pedal all the way out before the shift from 1st to 2nd, and riding it halfway thru 2nd, and 1/4 of the way thru 3rd.

Use that 3rd pedal! Whenever you sense wheelspin, quickly but smoothly use that 3rd pedal to regulate what makes it to the ground. "

[Rel44 M3]

Something weird happened to me this weekend. I was practicing one of those 4k rpm launches, and I swear the clutch wouldn't come up from mid-position. I was modulating it but then I tried to let the clutch all the way out but it was stuck there. I quickly pushed it back in and shifted, but it freaked me out. Does this thing usually happen? She's driving fine so I don't think I messed up anything, and if I did I don't notice it.

[SilverStreak]

I don't think that is "normal" per se, in that it's never happened to me. Maybe post about it in the E36 M3 forum... :

[paul e]

Dave, can you describe the workings of the lights on the christmas tree, and how to use them to your advanatage? If this info exists elsewhere, just direct me to it...Thanks.

[Rel44 M3]

I downloaded a little proggy from the Great Lakes Dragaway site that is basically a practice tree for you to get the timing down. Don't know how much it helps because I haven't gone there yet. The site is http://www.greatlakesdragaway.com

[SilverStreak]

Paul and Rel, keep something to keep in mind, all trees are similar, but none are identical, eventhough they "should" be. And mroe than anything, it also depends on you.

Some guys have tons of success launching just as the last yellow lights up, in combination with staging deep. Others, if they do that, will red light it half the time. Some stage shallow and go when the last yellow goes out, etc... you gotta find you're own technique.

Mastering the lights can't be taught, it has to be experienced, you gotta just do it a bunch of times and find what works best for you.

And practicing online is cute, but in all reality it's just soooo different when your left foot is riding the clutch, your right foot on the fun pedal, and you're right hand on the shifter with a ton and half of steel under you.

You gotta experience it!

[SilverStreak]

Another good question asked of me recently:

"I've re-read your thread recently, and one thing that keeps popping up which you haven't been asked before (at least in public) is... how do you RIDE your clutch just prior to launching, and keep the RPM steady, without INCHING the car forward (and hence passing the staging light, and red-lighting)?"

Answer:

"Well, that depends track to track. Some tracks have grooves in the staging lane, so if you don't over do it, you will just sit there- remember the key is you're not doing a burnout, you're on the brink where it's grabbing-- so you rev it up to where you know you can launch, and let out the clutch, just as it's grabbing, adjust, and in effect just sit there.

Sometimes, I need to use my left foot on the clutch, and my right heel on the brake (just enough to hold me on the line) and my right toes (and ball of my feet) on the gas- if need be."

[SilverStreak]

First, you need to dyno your car, cuz every car can be unique (especially if you have any mods at all, no matter how insignificant).

Next, we need to know your gear ratios, and you're rear diff ratio, what it all comes down to is you want to upshift where your tach will fall in the next gear, right at torque peak.

BMW's are actually speaced well for shifting at redline in 1st and 2nd gear, and about 150-200 rpms shy of redline in 3rd gear.

Mustangs, 5.0's, torque peak is lower, so shifting a couple hundred rpms shy of redline (on a stock 5.0) works best. With the never 4.6, you can go to redline in 1st, but 200 rpms shy of redline in 2nd, and if you need it, 300 rpms shy in 3rd.

You have to experiment, practice, take 1st up to redline (gradually on a back road, you don't have go balls out for this) and shift, observe where the tach falls into 2nd. Do the same for 2-3, etc.

Then try to make it happen, again gradually, slowly, etc, so it falls to the torque peak rpm. Learn those #'s, and then practice it, gradually going faster, cuz when you're racing, things move faster. Meaning you should practice doing it slowly, not racing to learn the #'s. But when under wide open throttle things go by faster, so practice. Cuz if you're shift point is 5600 rpm, if you are trying to shift at that point during a race and you have not practiced, you'll either react to slowly and shift at 5750-5800 rpm, or try to anticipate too much and shift at 5400 rpm, all of which costs you a few tenths.

And drag racing is all about tenths. And mastering dozens of tiny little nuances, all of which equate to a few tenths, each. That's why it takes tons of practice, just doing it, to get your mind/body connection to work well.

It's like racquetball, once your body learns how to react to given situations, you get that physical memory down. For the launch, feeling the traction barrier with your left foot. The shift points, etc...

[jibberia]

I think everyone who does drag racing should try racing motocross on a 125 bike. These things make about 30-38 hp and weigh 200lbs, but the power usually comes on way up high. you have to shift a bunch and the clutch is... well the clutch is key. You have to be completely comfy with murdering your clutch, using it ALL the time to keep the bike revving in the power range to apply power to the wheel.

Most 125 mxers say "only use the clutch to start and turn" which is quite true... well you shift w/o the clutch (another story entirely) but whenever you slow down and accelerate, clutch comes into play.

I'm not much of a drag racer... just don't feel like buying a new clutch for the bimmer, but the few times that I've done it I've been comfortable with using the clutch, and I think for beginners (like myself ) that's the most important thing to master.

Maybe everyone should go spend a grand or 2 on a 125 and learn!

[civic4982]

on a FWD car, would the tire pressures be reversed? Also, what should I look for in FWD launchig?

[SilverStreak]

Yes, drop the fronts, raise the rears, and more than ever you need to really ride the clutch on launch to avoid a sudden weight shift, which takes weight away from where it's needed most on a FWD.

[zenon]

Ask dave the drag racing professor anything!

thanks dave!

[SilverStreak]

That's what I'm here for...

[CSBM5]

Dave,

Question regarding roll-out in timing 1/4 mile runs. I recently got an Escort G-timer, and one of the setup options is roll-out, specified in inches, from 0" to 20". In order to measure pure acceleration (i.e. 0-60), I set the rollout at 0".

My question is in regard to 1/4 mile strip times. I assume that these are not "pure" accerleration times, meaning there is always some rollout that is not timed? i.e. the car is moving some prior to the lights being tripped to start the timer? The G-timer recommends 12" to attempt to line up with the typical track by the way. So my novice drag racer question lingers...do the 1/4 mile slips represent pure movement from zero? I'm guessing that answer is no. If it is, then is the rollout different at different tracks?

[SilverStreak]

Hey Chuck, roll-out can vary track to track. The ET clock does not start ticking until you cross the line/break the beam.

Some experienced guys stage right on the line. Some guys, generally those less comfortable with their launch will stage back as far as possible (again depends on the track) and break the beam with a little momentum.

12" may sound like a lot, but it's not. Go lay a ruler in front of the forward most point of your car (likely your bumper or front license plate frame depending on where you live) and see if you can hold it in place while revving it up, modulating the clutch, etc, without moving the car at all.

[CSBM5]

Thanks for the info Dave! Escort points out that assuming your can accelerate at 0.5g from a stop, a 12" rollout would equal 0.35 seconds, an 8" rollout 0.29 seconds. Getting accurate acceleration times is really dependent on this value as I have found. I assume most car mags in there tests are measuring absolute zero to 1/4 mile times? (i.e. something like Car and Driver who use on board timing instrumentation).

I hate to sound picky, but I'm just trying to understand how to compare acceleration times at a strip versus timed on something like a G-timer. Thanks again! I guess I should input a rollout value to simulate a 1/4mile run at a strip? Man, I'm confused.

[SilverStreak]

I think the rags correct for 0 rollout. I personally stage right at the line, but then again, I don't need the room, I've got 8000 runs under my belt...

Most often what you'll find with inexperienced guys is that they stage and try to take advantage of that 6-12", but 99% of the time, they launch spinning wheels, which screws up the ET somewhat but provides a nicer trap speed....

If you feel you can hold the car in place before launching, set it at 0, or maybe real low, like 3"...

[CSBM5]

Dave,

You should edit this thread earlier as incorrect information was given. You were MUCH closer in your estimate of the weight of gasoline!

At 68F (density does not vary much with temperature as it does with a vapor):

Gasoline: 6.15 lb/gallon

Water: 8.34 lb/gallon.

I thought the value posted by the banned poster looked way too high (but it has been 25 years since thermo class ), so I looked up the density values again and double checked my calculations.

[Juan ///M325]

Originally posted by SilverStreak


Most often what you'll find with inexperienced guys is that they stage and try to take advantage of that 6-12", but 99% of the time, they launch spinning wheels, which screws up the ET somewhat but provides a nicer trap speed....

If you feel you can hold the car in place before launching, set it at 0, or maybe real low, like 3"...

Dave:

Before I move on with my question let me give you my info:

'95 325 AA supercharged

264 RWHP 222 lb tq SAE

3:46 rear

Yokos ES 100 235/40/17 @ 29 psi

Rookie Driver


I'm glad I read this thread. I just went to the track for the second time. The first time was about two weeks ago. With a sliping clutch, I managed to run a 15.4. I never had a chance to run again, the clutch was dead (original with 113k miles).

I went today to try out my new clutch (sachs sport). I tried different ways to launch the car, but experienced the same results. When accelerating in 1st, I had no traction. When shifting to second, I would ride the clutch but when steping on the gas I'll loose traction. These were my results:


1st race.....1/4 14.314 MPH 99.26 60' 2.1

2nd .......1/4 14.237 MPH 100.00 60' 2.2

3rd ........1/4 14.259 MPH 100.34 60' 2.21


I really feel that the car should be running in the mid to lower 13s' because on how it pulls once I'm past the 1/8.


Do you think the same? Should I try drag radials? BTW, I was running with everything in the car (spare, jack, ect). Temp. was 55 degrees, low humidity close to sea level (I live in Maryland).


Thanks for your helpful tips and advises.....


Juan

[SilverStreak]

Thank you, Chuck!

Juan, with your trap speed right around 100 mph, and your 60' times around 2.1-2.2, I'd say on street tires you can certainly break into the 13's.

And with DR's on there, I'd expect mid 13's, maybe low 13's, given your traps.

As an example, back when my car was bone stock, I ran 13.89 at 99.5 mph on street tires with a 1.8x 60' time. I slapped on DR's, and ran a 13.65 at 99.1 mph with a 1.6x 60' time.

My car did not have the hp that yours does, but it is lighter. Power to weight ratios being what they are, your car is still hitting 100 mph traps, a good 1 mph faster than what my car used to do when it was stock, plus I was running in colder weather and closer to sea level.

The drag radials are gonna make a huge difference for you at launch, especially if traction is the issue you say it is. And you'll have the ability to warm them up before a run, where with street tires, the best you can really hope to achieve (especially in the winter months) is to simple clean them off of debris, etc.

I would definitely try DR's, get a cheap set of rear wheels, as wide as you can, and get the wide and tall set of DR's back there. Tall is key, cuz you want sidewall flex for drag racing.