Best way to launch in NO4?

Michael Czeiszperger · **Joined:** Thu Apr 09, 2009 9:35 am **Posts:** 861

Keith Vail wrote:

I used to rev the Legacy up to about 4500-5k and dump the clutch. You get wheelspin so it is not hard on the driveline at all.

And you know this is faster because? I can see where this would get you wheelspin immediately, its just I can't see why this is fastest...

Michael Czeiszperger · **Joined:** Thu Apr 09, 2009 9:35 am **Posts:** 861

Keith Vail wrote:

I used to rev the Legacy up to about 4500-5k and dump the clutch. You get wheelspin so it is not hard on the driveline at all.

Well, its still working so you must be right. I can see where this would get the most wheel spin, but why is it the fastest launch technique?

RichardNuss · **Posted:** Wed Nov 18, 2009 3:47 pm

Michael Czeiszperger wrote:

And you know this is faster because? I can see where this would get you wheelspin immediately, its just I can't see why this is fastest...

Because you know you're generating the max launch force. If you haven't spun the tires, then who knows if you could have thrown some more power to it? I realize that there is some theoretical magic point with zero wheelspin and you putting down max power that your traction can handle, but you can't be that exact.

It also gets you into the RPM range more quickly where you are generating power (less bog), especially on a turbo car.

Consistently in road tests, cars are faster with the traction control off, and allowing just a bit of wheelspin off the line.

Now, if you just sat there spinning - that would be an issue. But with race tires, few (if any) of the AWD cars at a THSCC event would just sit there and spin.

KouroshNeshat · **Posted:** Wed Nov 18, 2009 3:49 pm

im pretty sure we can dig up the physics behind it, but in plain words...

you want the tires to hook. try just jamming on the gas like you're taking off from a stop light (while just casually letting off the clutch) and see how long it takes for you to get up to speed. then do the same thing while dropping the clutch (but dont, i dont want you to mess yer trans up)..

you get out of the hole quicker. you've got 4 tires that need some power behind them to get them to move. but you dont want to rev too high. and thats where some test and tune will set you right with where you want to rev. but since most of use have very similar cars, the same range applies to a lot of us.

watch some drag races on you tube.. you'll see how quick those guys can get off the line while revving high.

RichardNuss · **Posted:** Wed Nov 18, 2009 3:49 pm

Keith Vail wrote:

Richard that noise is probably from the rear diff moving when you dump the clutch. STi's do it on pavement when you launch them if you haven't upgraded to stiffer mounts. The stock bushings allow the diff to move and hit the floor. I have driven a few STI's that will do it on a hard 1-2 shift if the bushings are getting worn.

That's what I'm thinking (hoping). It will do it on hard launch and hard shifts. We just haven't had time to mess with it.

KouroshNeshat · **Posted:** Wed Nov 18, 2009 3:51 pm

RichardNuss wrote:

Keith Vail wrote:

Richard that noise is probably from the rear diff moving when you dump the clutch. STi's do it on pavement when you launch them if you haven't upgraded to stiffer mounts. The stock bushings allow the diff to move and hit the floor. I have driven a few STI's that will do it on a hard 1-2 shift if the bushings are getting worn.

That's what I'm thinking (hoping). It will do it on hard launch and hard shifts. We just haven't had time to mess with it.

Rays car makes a similar sound. and its loud from inside the car. lol. but that hasnt stopped him!

Keith Vail · **Posted:** Wed Nov 18, 2009 4:32 pm

KouroshNeshat wrote:

Rays car makes a similar sound. and its loud from inside the car. lol. but that hasnt stopped him!

It really shouldn't be doing any damage. There is a rubber bumper on the top of Subaru rear diff's. So you are hearing the bumper hit the floor. It is essentially like a pinion snubber on an old live axle car.

Michael, I don't know that is it the fastest way. My options were bog off the line, spin the tires or slip the crap out of the clutch. I hate bogging off the line and I didn't feel like burning up the new clutch I put in the car when I bought it so I just launched it so it would spin tires off the line enough to get the engine up into it's powerband.

Michael Czeiszperger · **Joined:** Thu Apr 09, 2009 9:35 am **Posts:** 861

Keith Vail wrote:

Michael, I don't know that is it the fastest way. My options were bog off the line, spin the tires or slip the crap out of the clutch. I hate bogging off the line and I didn't feel like burning up the new clutch I put in the car when I bought it so I just launched it so it would spin tires off the line enough to get the engine up into it's powerband.

Thanks, I appreciate that your advice. What do these terms mean?

1. Bogging off the line?
2. Slip the crap out of the clutch?

Remember I don't know anything about cars or car parts other than a primitive idea of what a clutch does. Are you saying that the clutch should be let out slowly, or released all at once? I also don't want to burn out the clutch in your old car!

Keith Vail · **Posted:** Wed Nov 18, 2009 4:41 pm

Michael Czeiszperger wrote:

Thanks, I appreciate that your advice. What do these terms mean?

1. Bogging off the line?
2. Slip the crap out of the clutch?

Remember I don't know anything about cars or car parts other than a primitive idea of what a clutch does. Are you saying that the clutch should be let out slowly, or released all at once? I also don't want to burn out the clutch in your old car!

Simply put. Bogging off the line is basically a typical street launch. You let the clutch out without revving the engine much. There is no shock to the drivetrain and you are slow to get away. If you let the clutch out slowly with the engine revved up you will get away decently quick but you will burn the clutch up faster because you are partially engaging the clutch against the flywheel that is spinning rather fast. Not healthy for a clutch.

If you just rev the engine and let the clutch out fast you then get wheel spin and the clutch isn't abused. On dirt the driveline does not shock too much because the torque goes out the tires as they spin and is not absorbed by the driveline.

Michael Czeiszperger · **Joined:** Thu Apr 09, 2009 9:35 am **Posts:** 861

Keith Vail wrote:

If you let the clutch out slowly with the engine revved up you will get away decently quick but you will burn the clutch up faster because you are partially engaging the clutch against the flywheel that is spinning rather fast. Not healthy for a clutch.

Arggg! I've done that the couple of times I've autocrossed :-(

I've learned something, thanks.

By "letting the clutch out fast" do you mean just letting the foot slip off of it so it pops up by itself, or just lifting the left quickly?

KouroshNeshat · **Posted:** Wed Nov 18, 2009 5:10 pm

just lifting off of it quickly.
BTW.. dont do this on the street. since you'll most likely get traction, it may hurt your car.

the dirt isnt much of an issue from what has been posted earlier in this thread. but just a warning to ya.

Kevin Allen · **Joined:** Thu Aug 28, 2003 6:42 pm **Posts:** 3479

There's more to it than has been explained so far. If you can come to the setup day, I'll help you out.

Vincent Keene · **Posted:** Wed Nov 18, 2009 5:23 pm

Keith Vail wrote:

I seem to remember for the longest time you told me I was one of the few that would actually launch my AWD car off the start. :lol:

Correct, and I stand by that statement...but since you haven't been out in a while, Mark consistently has the best launch now IMO.

Charlie Guthrie · **Joined:** Thu Aug 28, 2003 8:14 pm **Posts:** 832

Michael C wrote:

Quote:

Thanks, I appreciate that your advice. What do these terms mean?

1. Bogging off the line?
2. Slip the crap out of the clutch?

I can't believe that no one has jumped up to explain "number two"

"Slipping the Crap out of a clutch" is allowing the brown smoke to escape. So named because of the poop like smell and the common expletive heard when the owner gets the repair bill.

Sort of like the expletive I uttered last night as we tried unsuccessfully to resuscitate the DirtMaster. Unfortunately the DirtMaster is dead. Intake valves recessed into the head until there was zero valve clearance and ultra low compression. I'm not looking forward to using my '87 daily driver as a rally-x car.

Vincent Keene · **Posted:** Fri Nov 20, 2009 9:21 am

Charlie Guthrie wrote:

Sort of like the expletive I uttered last night as we tried unsuccessfully to resuscitate the DirtMaster. Unfortunately the DirtMaster is dead.

So that means the General Lei is the winner in the rally beater longevity test!

Sorry to see the old boy go though. Much like the General you guys have gotten about 100X your monies worth out of it.

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Best way to launch in NO4?

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