Launch RPM

[weedburner]

Originally Posted by btrc

Just curious about the Coyote Stock guys. What transmission are the fast ones using? 4 speed, 5 speed?

They are allowed to select from a menu of approved 5 and 6spd transmissions and ratios. 4th is always 1:1, so they only use 1-4 and generally remove the overdrive gears. I might add that they are required to shift using the clutch, no clutchless shifts allowed. Here's a link to their '16 rules... http://www.nmradigital.com/dl/rules/cs.pdf

Permitted Manual Transmissions:
1. Tremec T5
2. Tremec T45
3. Tremec T56
4. Tremec TR3550
5. Tremec TR3650
6. Tremec TKO
7. Tremec TKO-II
8. Tremec TKO500
9. Tremec TKO600
10. Ford Getrag

[weedburner]

Originally Posted by CJME

This is a strip only car. Current clutch is a non adjustable Ram powergrip (Sintered iron/Organic). The trans has a 2.20 first gear. Engine is a 12.5:1 iron headed 327 running on VP 110. Is there a way i can get the clutch to slip more on the launch? I will try raising air pressure.

Here's a few options...

1- less aggressive disc
2- smaller diameter disc or reduce the effective diameter of the disc you have
3- reduce clamp pressure by either swapping to a weaker PP/spring or shimming your existing PP away from the flywheel
4- temporarily hold back some clamp pressure with your foot, basically ride the clutch out for 5-10 feet. Adding an adjustable spring loaded pedal stop can make it easier to consistently find the sweet spot in the pedal travel
5- temporarily hold back some clamp pressure with a timed mechanical device

[Stephen & Horace Johnson]

Originally Posted by weedburner

They are allowed to select from a menu of approved 5 and 6spd transmissions and ratios. 4th is always 1:1, so they only use 1-4 and generally remove the overdrive gears. I might add that they are required to shift using the clutch, no clutchless shifts allowed. Here's a link to their '16 rules... http://www.nmradigital.com/dl/rules/cs.pdf

Permitted Manual Transmissions:
1. Tremec T5
2. Tremec T45
3. Tremec T56
4. Tremec TR3550
5. Tremec TR3650
6. Tremec TKO
7. Tremec TKO-II
8. Tremec TKO500
9. Tremec TKO600
10. Ford Getrag

They are using the gforce 101A trans. All those listed above were breaking like toothpicks!!

[weedburner]

Originally Posted by Stephen & Horace Johnson

They are using the gforce 101A trans. All those listed above were breaking like toothpicks!!

Sorry, i copy/pasted from the original '16 rules instead of the mid-season update, didn't notice that the additions were not on there...

• G-Force –G101A, GF4A – 2.933, 1.867, 1.333, 1.000
3.000, 1.870, 1.340, 1.000
3.173, 1.960, 1.346, 1.000
3.252, 2.009, 1.380, 1.000
3.300, 2.100, 1.406, 1.000
• Jerico –DR4 -
• Liberty -LCS 5000 4-Speed**
• Andrews Transmission –A431 H-Pattern 4-speed**
**Contact NMRA Tech Department for permitted gear ratios

[Sean Marconette]

Originally Posted by terry1

What would be an acceptable drop in RPM between the launch RPM and when the clutch is released?
Terry K

Terry,
On my car I keep the rpm drop to around 2000 and the clutch lockup on launch no more than 0.9 seconds. .9 seconds is too loose, and is based on the input shaft moving till the engine and input shaft rpm are the same. A general rule has been .3 to .8 on lockup. If you start getting to .3 the clutch may drag the engine down way too much and then the engine struggles to recover. This is where data acquisition is money well spent and can help you maintain clutch maintenance and performance.

Sean

[weedburner]

Originally Posted by Sean Marconette

Terry,
On my car I keep the rpm drop to around 2000 and the clutch lockup on launch no more than 0.9 seconds. .9 seconds is too loose, and is based on the input shaft moving till the engine and input shaft rpm are the same. A general rule has been .3 to .8 on lockup. If you start getting to .3 the clutch may drag the engine down way too much and then the engine struggles to recover. This is where data acquisition is money well spent and can help you maintain clutch maintenance and performance.

Sean

I've found that clutch slip time usually overlaps a bit with tire slip time, so i'm thinking your overall slip time between the engine and track is likely longer.

I'm dead hooking with radials, so the clutch does all the work. It seems the longer i let the clutch slip the faster it goes, for me around 1 sec is a good compromise. I shoot for zero rpm drop but when a 500 drop is spread over a second or so, it makes little difference.

Grant

[Jim Caughlin]

What's the ideal launch RPM? As much as your engine, chassis and tires will handle. In my case, the 2 step is set at 8400 but the one time that it failed and I left at well over 10,000 netted me the best 60' that I've ever had. Not brave enough to repeat that but you don't see Comp cars or Pro Stockers leaving at anything less than kill.

I am in agreement with most of the other comments here. Without a good slipper clutch and some form of data logger, you're pretty much twisting in the wind. The days of 40 pound flywheels and 3500 pound dead lock up clutches are gone unless you want to go slow and break parts. My flywheel and clutch assy weighs well under 20 pounds total. There are huge performance advantages in reducing flywheel & clutch diameters and weight.

Jim Caughlin
SS 6019

[Sean Marconette]

Originally Posted by weedburner

I've found that clutch slip time usually overlaps a bit with tire slip time, so i'm thinking your overall slip time between the engine and track is likely longer.



Grant

I am not sure where you think I guessed on my information? My results are from paying attention to how my clutch performs. My tires are not slipping otherwise I would see it with the data. 60' and ET are best for my combination at the info I posted. If my clutch does not lockup before .9 it shows on the time slip.

[james schaechter]

Originally Posted by weedburner

I've found that clutch slip time usually overlaps a bit with tire slip time, so i'm thinking your overall slip time between the engine and track is likely longer.

I'm dead hooking with radials, so the clutch does all the work. It seems the longer i let the clutch slip the faster it goes, for me around 1 sec is a good compromise. I shoot for zero rpm drop but when a 500 drop is spread over a second or so, it makes little difference.

Grant

I find this very interesting. Dead hooking on radials with zero drop? And the clutch is doing the work? I would expect that the clutch is slipping or the tires are spinning. Or the chassis works extraordinarily well with radials and the engine is an absolute beast! Tell me more. What type of radials? Weight of car? and what Are your incremental Times? Thanks, Jim.

[weedburner]

Originally Posted by Sean Marconette

I am not sure where you think I guessed on my information? My results are from paying attention to how my clutch performs. My tires are not slipping otherwise I would see it with the data. 60' and ET are best for my combination at the info I posted. If my clutch does not lockup before .9 it shows on the time slip.

Sorry, didn't mean to imply that you were anything but accurate in what you wrote.

When i saw .3 to lockup, that usually means the tires are getting knocked loose unless there's a ton of SLR involved. If my car locked up at .3 from 1st movement and the tires were stuck, it would suck the engine all the way down to around 1800 rpm if it didn't break something first.