launch control... school me.

[740ATL]

Ok... so Adrian sends me this video of a VW with MS launch control/flatshift. It's insanely cool. The base-teenage-hormone-driven-alpha-male-practical-joker side of me wants it simply to make flames in stop and go traffic to piss off the ES driving yuppies which permeate the Atlanta suburbs... I digress.

... but I find that I really have no clue what it does other than make flames.

Then I do some searching and find out it can actually be useful in drag racing... something about being able to hold the gas pedal to the floor but the engine will only rev to a pre-set limit thus being able to shift without over-reving the engine.... at least that's my initial knowledge of it.

That sounds interesting enough, but does it really work? I have a getrag-3.73 equipped 16v turbo car. At the strip, my car will only reach about 6psi in first gear... I'm including a datalog snippet of one of my drag race logs.

So... how is launch control going to help me? Keep in mind, I already have the wiring built in to the daughter card... I just need a clutch switch.... I'm more concerned with how/why it works... not the wiring.

Mike

[Morten VJ]

Yes it will work it would even allow you to flatshift..
But it won't repair your wildly fluktuating Batt voltage.
Fix it first, and you would get a better running engine.

BR

Morten

[740ATL]

Morten. Thanks for the reply.

I have no idea what flatshift is... hench my post.

Thanks for the battery voltage suggestion... it has been an ongoing problem. ALso keep in mind the scale of the battery voltage...

regards,

Mike

[Morten VJ]

flatshift is when you change gears you dont lift the trottel it will just rewert to the lanchcontrol rpm.
And you dont need a stinking ricer Bow.

Your batt voltage stinks.
Are you using the old LH harnes, this might be your problem.
A simpel dvm. could get your answers.
It looks like a bad connektion.
The voltage regulator+battery can't make those ups and downs.

BR

Morten

[Matt Dupuis]

It's been a while since I investigated launch control, but there used to be two ways of doing it: One was by using an arming switch and a clutch pedal switch and a permanently preset RPM limit; and the other was to use a momentary button on the steering wheel/shifter and an RPM limit that's set every time you use the button.

The clutch pedal switch would give you the same launch RPM every time you use it, so it's simple to use. It's not so simple to hook up, though, 'cause you've got to set it up so that it disengages right around your friction point, and on a cable clutch that point can move around quite a bit as the clutch wears - even on a hydraulic, it seems to move around some.

The momentary button doesn't need an arming switch, so it's always on. This allows you to use it even when you're in gear, like for heating the tires in a water box for example. Every time you press the button, MS samples the RPM you're currently at and uses that as it's upper limit. This lets you hold the engine to 4000 RPM in the burnout box, 3200 at the lights, and 6500 on every shift. It also gives you the ability to change your launch RPM at your merest whim, like for example you've got the tires nice and hot but the track is cooling off and the guy next to you is taking a long time to get staged, so you need to drop launch RPM by 200 or so. The only "skill" related variable is when do you release the button?

At one point MSnS-Extra allowed either method, but I don't know if they do anymore 'cause it's been a couple years since I would have needed it, and I haven't messed with the -Extra stuff in a while.

Your wildly fluctuating voltage might be nothing more than a cruddy fusebox.

This belongs in Aftermarket EMS or Maintenance, depending on which way it goes.

[towerymt]

One thing worth mentioning is that the clutch switch will give you the flat shift ability, but the momentary switch really wouldn't work well for that. I think the upper limit on launch rpm was something like 3500, so if the button is pushed, you can't go over 3500rpm. With the clutch switch, even though you may shift at 7000, when the button is pushed by the clutch pedal, it will try to keep it at 3500 (obviously it can't drop the rpm that much in a fraction of a second). It's a spark drop rev limiter that kicks in when you press the clutch to shift, so the engine won't over rev while your foot is flat on the floor.

We set it up on Rob's car and with a little bit of playing with the numbers, it was holding 10psi in neutral at ~3000rpm and shooting fire with the popping noise you're familiar with. The fire wasn't as good as it was from my car, though (no turbo in the way ;-) ).

I had mine hooked up to an on/off switch that was not momentary. Since the upper rpm limit was ~3500, if I turned it on I could test out flat shifting....but my shift point was below 3500. It did work as it was supposed to, though. But it would be very tricky to try to hit a switch and time it with your shift, so you should probably set up the clutch switch.

You'll need a lot of tire to leave the line under boost, so you may not even find it useful as launch control. But flat shifting will help, because it should maintain boost while shifting since it's still firing fuel but dropping spark, which is how it builds boost in neutral.

[Violet Grumble]

My understanding of launch control is similar, but the point of it being that you can build boost on the spot (similar to a transbrake). Going from experience in my brother's WRX, he programmed the Haltech to limit the revs at 5000rpm whilst launch control was engaged through a small button he installed next to the handbrake. Once the clutch is depressed and the button held down, you floor the throttle and the car will rev to 5000, and begin rev limiting at that point, whilst changing the timing so that the exhaust valves open sooner, allowing combustion to occur outside the cylinder, and into the turbo, causing it to spool up. Hence the shots of fire out the exhaust and the very loud popping sound. Launch boost is preset, in this case 10PSI, and once the desired boost is reached, the clutch is dropped hard, followed by releasing the launch button a moment later (to prevent tyre spin). Once the button is released the car returns to normal and is free to rev to redline. This way turbo lag is eliminated on a launch. Though be mindful, it is very stressful on the rest of the driveline, so use it with care.

I'd say launch control employed in the above way would be useless on an N/A car, and while the popping sound and fire out the exhaust is spine-tinglingly fun, would serve no other purpose. Most decent new aftermarket ECU's support a launch control feature, it's just a matter of wiring up your launch button and setting the RPMs and boost levels.

[740ATL]

Wait this is even cooler than I thought...

so I mash the gas pedal... it goes to a pre-set RPM, retards the timing like crazy, lets me build boost, then when I take off and get to the 2nd gear shift, I don't have to lift the gas pedal?

That's gonna cause problems... for my tires. I love it.

Thanks for the voltage suggestions guys... I measured 14.4v at the battery and 12.8v at MS... Then I bumped the wiring and caused the IAT, CLT, and O2 gauges to shut off while running. I hate wiring.

Mike

[B Mac66]

holy crap. can somebody PULEASE get a video of this?? this is cooler than mg bs doing burnouts

[towerymt]

Wait this is even cooler than I thought...

so I mash the gas pedal... it goes to a pre-set RPM, retards the timing like crazy, lets me build boost, then when I take off and get to the 2nd gear shift, I don't have to lift the gas pedal?

That's gonna cause problems... for my tires. I love it.
It drops spark to control engine speed instead of retarding the timing. That's why you get the fire, cause the fuel is still going through w/o the spark event. There was a time or two at SE when I was messing with the launch control settings in MS and I changed the rev limits and then floored it, and it sounded like I had a clogged cat...like a soft limiter that retards timing. I think that's when the soft limit value is lower than the hard limit value, but I don't remember.

If you want video of my car doing this, it's in the SE vid a couple times. I know for sure it's on the dyno vid which would have been saturday afternoon.

http://mason.gmu.edu/~mtowery/PICT0270_fire.jpg

[towerymt]

http://mason.gmu.edu/~mtowery/PICT0343_launch_.jpg

[740ATL]

I know what I'm doing this weekend.

Thanks guys!

[vthreat]

It drops spark to control engine speed instead of retarding the timing. That's why you get the fire, cause the fuel is still going through w/o the spark event.


so if one is using EDIS with MS can we still use this feature or no?

[Moridin]

The clutch pedal switch would give you the same launch RPM every time you use it, so it's simple to use. It's not so simple to hook up, though, 'cause you've got to set it up so that it disengages right around your friction point, and on a cable clutch that point can move around quite a bit as the clutch wears - even on a hydraulic, it seems to move around some.


Just set up the switch so it disengages at the top of the clutch pedal. As soon as the clutch is slightly depressed, you're set for flat shift.

[adrianpike]

so if one is using EDIS with MS can we still use this feature or no?

Nope.

edit: not yet and/or easily. :twisted:

[Violet Grumble]

Here's a video of launch control in action. It's my sister-in-law's WRX driven by my brother, it is the far car in the video (silver one). The video has only one pop in it, though you can sit on launch control all day if you want to and have it pop and bang and make noise, say goodbye to your cat though. The beauty of this type of launch control is that boost builds much quicker than a transbrake, as they take forever to build up, some transbrake equipped dragsters take the time of their competitor already completing their pass before they have built enough boost to launch. The difference though is that on a transbrake the driveline is already engaged, whereas on launch control it isn't. Launch control is more suited to AWD cars or those with high traction as on regular RWD cars you'll just end up spinning on the spot. The noise is obscenely loud and you'd never get tired of it though.

Anyway, here's the video.

http://www.nandor.net.au/pics/AdrianvsNandorknockout.avi (http://www.nandor.net.au/pics/AdrianvsNandorknockout.avi)

[740ATL]

Adrian, where's that damn video! :nod:

[MrBill]

I hope ms2 can do this soon:(

[The Aspirator]

Adrian, where's that damn video! :nod:I was just about to ask that too!

[The Aspirator]

Anyway, here's the video.

http://www.nandor.net.au/pics/AdrianvsNandorknockout.avi (http://www.nandor.net.au/pics/AdrianvsNandorknockout.avi)Holy crap when are we going to have autocrosses like that!???

[adrianpike]

god you guys are insistent:
http://files.lbrt.dk/movies/diverse/megasquirt/launchcontrol.wmv

looks more like a ghymkhana to me than an auto-x. :-D

[The Aspirator]

Yeah, so? I still wanna do it! I'd love to see your 80000lb rear springs bouncing around the track sideways like that.

[adrianpike]

Yeah, so? I still wanna do it! I'd love to see your 80000lb rear springs bouncing around the track sideways like that.

Find me a parking lot and a garden hose. :ninja:

[Violet Grumble]

Holy crap when are we going to have autocrosses like that!???

That's a motorkhana / skidpan event, I was present for that too but didn't make it to the final round of the shootout (sometimes you just can't beat AWD). We also have other events like Khanacrosses that are on dirt and can get to the top of 3rd gear. Great slippy slidey fun!