RPM Launch?

eXo5 · 05-07-2009, 02:59 PM

I typically launch from idle speed. Is this safest? And best for the 1/4? Just curious. Thnx

ChrisSlicks · 05-07-2009, 03:05 PM

Safest yes, but also slowest. Fastest is slipping the clutch at 2500-3000 rpm on the verge of wheelspin, puts a beating on the clutch long term though.

At auto-x I don't care about 60ft times so I usually just dump the clutch at around 3000 rpm and break the tires loose, feathering the gas to control wheelspin until it hooks up.

mspeasl · 05-07-2009, 10:58 PM

Quote:

Originally Posted by ChrisSlicks

Safest yes, but also slowest. Fastest is slipping the clutch at 2500-3000 rpm on the verge of wheelspin, puts a beating on the clutch long term though.

At auto-x I don't care about 60ft times so I usually just dump the clutch at around 3000 rpm and break the tires loose, feathering the gas to control wheelspin until it hooks up.

Question: About 45 years ago (before good drag tires), we learned to launch a car at about 3000 RPM's using half clutch and maintaining a constant steady RPM level until the tires griped. At that point full clutch and WOT were initiated. When I first got my 350 in August of 02 I went out to my favorite location to see how the car ran out of the hole. I launched the car like I have for all of the years and O’crap…………. The car left great and hard, but the clutch when attempting to engage it completely, it wouldn’t engage all of the way!!! The clutch was just slipping and the car was not gaining speed like it should. That was the last time I attempted to drag race the car from a standing start. Now almost 7 years later I have a new 370. I head out to my favorite location again to see how this car runs out of the hole. It’s O’crap all over again. What gives? Has anyone else had this experience?

Thanks

wstar · 05-08-2009, 01:14 AM

Quote:

Originally Posted by mspeasl

Question: About 45 years ago (before good drag tires), we learned to launch a car at about 3000 RPM's using half clutch and maintaining a constant steady RPM level until the tires griped. At that point full clutch and WOT were initiated. When I first got my 350 in August of 02 I went out to my favorite location to see how the car ran out of the hole. I launched the car like I have for all of the years and O’crap…………. The car left great and hard, but the clutch when attempting to engage it completely, it wouldn’t engage all of the way!!! The clutch was just slipping and the car was not gaining speed like it should. That was the last time I attempted to drag race the car from a standing start. Now almost 7 years later I have a new 370. I head out to my favorite location again to see how this car runs out of the hole. It’s O’crap all over again. What gives? Has anyone else had this experience?

Thanks

The technique you describe (with the half-engaged clutch) is basically overheating your clutch surface and making it slip (and eating a lot of life on it too). I killed a clutch in my Trans Am by doing this 2-3 times accidentally (in that car with its torque and the weak stock clutch, you had to drop your foot to the side and dump the clutch crazy fast. If you failed to get your foot out of the way in time, it would slow the clutch engagement enough to cause the exact scenario you're describing). I have no experience with doing this on Z's though, so take it for what it's worth.

6SPD_FTW · 05-20-2009, 05:03 AM

Nah! Nissan manuals have something messed up with the design. It's a pretty common problem in the Altima/Maxima VQ/MT vehicles. My previous 2007 Altima 3.5SE 6MT did this as well. If you slip the clutch at a high rpm too aggressively, something in the master or slave cylinder gets all screwy and looses pressure. When I took my Altima to the dragstrip, I can't count how many times this happened.

The clutch just sinks to the floor and won't come back up and you end up slipping. Frustrating problem.

SEVERAL 350Z/Altima/Maxima owners have had this happen in routine driving. Dangerous if you ask me!

Late,
Trav

ChrisSlicks · 05-20-2009, 09:48 AM

The clamping force of the clutch is a little light, lighter even than my G35 it would seem. I'm sure they did this to make it nice and smooth and easy to operate, but I don't think it's going to last very long even with the help of SRM. A high performance clutch will be the way to go when it wears out. Just make sure it is something that is street driveable, a heavy clutch with a light flywheel (if you change that while you're in there) is tough to drive.

ianthegreat · 05-20-2009, 03:43 PM

Quote:

Originally Posted by ChrisSlicks

Safest yes, but also slowest. Fastest is slipping the clutch at 2500-3000 rpm on the verge of wheelspin, puts a beating on the clutch long term though.

At auto-x I don't care about 60ft times so I usually just dump the clutch at around 3000 rpm and break the tires loose, feathering the gas to control wheelspin until it hooks up.

+1

What he said.

The HACK · 05-20-2009, 07:02 PM

Quote:

Originally Posted by mspeasl

Question: About 45 years ago (before good drag tires), we learned to launch a car at about 3000 RPM's using half clutch and maintaining a constant steady RPM level until the tires griped. At that point full clutch and WOT were initiated. When I first got my 350 in August of 02 I went out to my favorite location to see how the car ran out of the hole. I launched the car like I have for all of the years and O’crap…………. The car left great and hard, but the clutch when attempting to engage it completely, it wouldn’t engage all of the way!!! The clutch was just slipping and the car was not gaining speed like it should. That was the last time I attempted to drag race the car from a standing start. Now almost 7 years later I have a new 370. I head out to my favorite location again to see how this car runs out of the hole. It’s O’crap all over again. What gives? Has anyone else had this experience?

Thanks

Late model cars are usually saddled with a clutch delay valve to prevent driveline-shock to the system when you dump the clutch. The result is, if you're used to driving a manual from more than 10 years ago, and you drive the same way today on one of the newer manuals with plenty of power and torque, be ready for a very unpleasant surprise.

Get the car up on a lift, look at the end of the hard-line between the clutch slave cylinder and the master cylinder, and you will likely find a small device that's inserted between the lines that prevents the clutch from engaging rapidly.

WShade · 05-20-2009, 07:26 PM

Quote:

Originally Posted by 6SPD_FTW

Nah! Nissan manuals have something messed up with the design. It's a pretty common problem in the Altima/Maxima VQ/MT vehicles. My previous 2007 Altima 3.5SE 6MT did this as well. If you slip the clutch at a high rpm too aggressively, something in the master or slave cylinder gets all screwy and looses pressure. When I took my Altima to the dragstrip, I can't count how many times this happened.

The clutch just sinks to the floor and won't come back up and you end up slipping. Frustrating problem.

SEVERAL 350Z/Altima/Maxima owners have had this happen in routine driving. Dangerous if you ask me!

Late,
Trav

Happened to me in the G while digging out from a toll booth while on a road trip one time.

mspeasl · 05-21-2009, 12:23 AM

Quote:

Originally Posted by The HACK

Late model cars are usually saddled with a clutch delay valve to prevent driveline-shock to the system when you dump the clutch. The result is, if you're used to driving a manual from more than 10 years ago, and you drive the same way today on one of the newer manuals with plenty of power and torque, be ready for a very unpleasant surprise.

Get the car up on a lift, look at the end of the hard-line between the clutch slave cylinder and the master cylinder, and you will likely find a small device that's inserted between the lines that prevents the clutch from engaging rapidly.

Is this piece of $hit connected to the ECM in anyway that will prevent its removal?

The HACK · 05-21-2009, 01:19 PM

Quote:

Originally Posted by mspeasl

Is this piece of $hit connected to the ECM in anyway that will prevent its removal?

No, it's a mechanical piece. KillerBee may be stopping by tomorrow at B&M Racing and I might be there (I work next door). If they put his car up on the rack I'll see if I can take a picture of the clutch hydraulics and see if I can spot the clutch delay valve and see how difficult it would be to remove.

But I'm 99.9% certain it's there. I remember seeing it on my 350Z.

miguez · 05-21-2009, 01:31 PM

Gents,

Quote:

Originally Posted by ChrisSlicks

... so I usually just dump the clutch at around 3000 rpm and break the tires loose ...

When one says "dump" the clutch, are we talking about removing your foot from the pedal as rapidly as possible, without easing it out? Basically, moving your foot sideways so the pedal springs back? I can't imagine the forces on the entire system by doing that!

ChrisSlicks · 05-21-2009, 02:05 PM

Quote:

Originally Posted by miguez

When one says "dump" the clutch, are we talking about removing your foot from the pedal as rapidly as possible, without easing it out? Basically, moving your foot sideways so the pedal springs back? I can't imagine the forces on the entire system by doing that!

Yes, that is exactly what it means. The forces are high but limited by available traction, so usually the shock factor isn't as high as you might think. Mechanical differentials usually take the brunt of the abuse. Years ago I did manage to smash all the teeth off the spider gears on an old Datsun

GTRFAN · 05-22-2009, 03:46 AM

Quote:

Originally Posted by The HACK

Late model cars are usually saddled with a clutch delay valve to prevent driveline-shock to the system when you dump the clutch.

I have never heard of this in any Nissans I have owned. I launched the 370 on the test drive at 3800 ish and it hooked up nicely.

You just need to feel the wheel spin and throttle it with the right foot.

wstar · 05-22-2009, 08:42 AM

FYI, I played with footbrake launch RPMs on the 7AT last night on a deserted road, so I'd have some idea about behavior at the drag strip. The stall is higher than I thought it would be on a stock car, as I was able to get up around 2500 RPM while locked down with the brakes pretty easily. It might be possible to push it a little further even. In any case, 2500 RPM broke the back tires a little too hard, it pretty much just burned them through the redline in 1st and they didn't catch solidly until after the shift to second. Somewhere around the 1,800 range seemed to hook up more ideally, at least on a normal pavement surface. If the track is nice and grippy, might be able to get away with a higher RPM though.

05-07-2009, 02:59 PM	#1 (permalink)
eXo5 Enthusiast Member Join Date: Apr 2009 Location: delaware Posts: 368 Drives: skateboard w/ NAWWWZ Rep Power: 672	RPM Launch? I typically launch from idle speed. Is this safest? And best for the 1/4? Just curious. Thnx __________________ Remember kids, NAWZ energy drink will not make your car go faster.

05-22-2009, 08:42 AM	#15 (permalink)
wstar A True Z Fanatic Join Date: Mar 2009 Location: Houston, TX Posts: 4,024 Drives: too slow Rep Power: 3594	FYI, I played with footbrake launch RPMs on the 7AT last night on a deserted road, so I'd have some idea about behavior at the drag strip. The stall is higher than I thought it would be on a stock car, as I was able to get up around 2500 RPM while locked down with the brakes pretty easily. It might be possible to push it a little further even. In any case, 2500 RPM broke the back tires a little too hard, it pretty much just burned them through the redline in 1st and they didn't catch solidly until after the shift to second. Somewhere around the 1,800 range seemed to hook up more ideally, at least on a normal pavement surface. If the track is nice and grippy, might be able to get away with a higher RPM though. __________________ 7AT Track Car! Journal thread / Car setup details

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05-07-2009, 03:05 PM	#2 (permalink)
ChrisSlicks A True Z Fanatic Join Date: Mar 2009 Location: North East Posts: 6,203 Drives: 09 370Z Sport M6 Rep Power: 653	Safest yes, but also slowest. Fastest is slipping the clutch at 2500-3000 rpm on the verge of wheelspin, puts a beating on the clutch long term though. At auto-x I don't care about 60ft times so I usually just dump the clutch at around 3000 rpm and break the tires loose, feathering the gas to control wheelspin until it hooks up.

05-20-2009, 05:03 AM	#5 (permalink)
6SPD_FTW Base Member Join Date: May 2009 Location: Bristol, VA Posts: 59 Drives: 09 370Z Bl 6MT Rep Power: 16	Nah! Nissan manuals have something messed up with the design. It's a pretty common problem in the Altima/Maxima VQ/MT vehicles. My previous 2007 Altima 3.5SE 6MT did this as well. If you slip the clutch at a high rpm too aggressively, something in the master or slave cylinder gets all screwy and looses pressure. When I took my Altima to the dragstrip, I can't count how many times this happened. The clutch just sinks to the floor and won't come back up and you end up slipping. Frustrating problem. SEVERAL 350Z/Altima/Maxima owners have had this happen in routine driving. Dangerous if you ask me! Late, Trav

05-20-2009, 09:48 AM	#6 (permalink)
ChrisSlicks A True Z Fanatic Join Date: Mar 2009 Location: North East Posts: 6,203 Drives: 09 370Z Sport M6 Rep Power: 653	The clamping force of the clutch is a little light, lighter even than my G35 it would seem. I'm sure they did this to make it nice and smooth and easy to operate, but I don't think it's going to last very long even with the help of SRM. A high performance clutch will be the way to go when it wears out. Just make sure it is something that is street driveable, a heavy clutch with a light flywheel (if you change that while you're in there) is tough to drive.