Launch RPM

[CJME]

I run a 327 68 Camaro at 3300lbs and i have a bog at launch. M22 trans with a dana 60 rear, 5.38 gears. I currently do not run a 2 step and launch around 5K by ear. should i slip the clutch or side step at 7K? I'm wanting opinions from experience, thanks.

[Sean Marconette]

What kind of clutch? And why not have a 2 step? From a consistancy standpoint a 2 step will allow you to mat the gas and leave at a set RPM every time and allow you to concentrate on the tree.

A stock trans and aggressive clutch is not going to have a good outcome if it hooks. An alternative to not hurting parts, is to add air to the rear tires to aid in a somewhat controlled wheel spin. If you launch it at 7000 RPM and it hooks you are liable to find the weak link in the trans for sure. We only side step the clutch that is adjustable to slide. Even an adjustable clutch set too tight can tear up parts. Just some quick thoughts.

More information is needed on the engine and clutch. Is the car street/strip or strip only?

Sean

[Joe Martens]

What is the first gear in the trans?

[Rod Greene]

If you are not using a 2 step and the throttle is not to the floor the secondaries have not opened. So Back in the day (mid 70's) it took a lot of work to make the carb work right with the high pressure clutches and tires we had. Go buy a 2 step makes it easier. One less thing to worry about. Don't those chevy transmissions have a real high first gear like 2.20 or such? That is a problem also.

[weedburner]

If you want less bog, i would recommend reducing your clutch's clamp pressure to more closely match your engine's power. That will raise your engine's average rpm, which means your engine will be able to produce more power over the same amount of time. It also reduces the amount of torque your clutch will draw on launch and after the shifts, which will help keep your M22 alive.

On launch, less clutch slows your rate of rpm loss when you dump the clutch, so it takes longer for engine rpm to drop far enough to sync up with wheel speed. By delaying the sync’ing of engine rpm and wheel speed (clutch lockup) to a point farther down the track, the car will have had more time to accelerate so it will be traveling faster. Basically, rpm won't dip as low because the car will be traveling faster when things sync up. Same thing happens after the shifts, which means recovery rpm will be better after all the shifts down the track. It all adds up to the engine being able to pack more revolutions of power production into the run. A 500 rpm improvement on after shift recovery is not uncommon with a well matched engine/clutch package.

If you simply air up the tires until they spin you will get much the same effect on launch, but there will be little if any spin after the shifts which means engine rpm would get dragged down lower after the gear changes, effectively lowering your average rpm. Adding air also reduces traction which helps your M22 live thru the launch, but since the tires won't likely spin after the shifts, your M22 would then still suffer the full hit from your current clutch.

The benefits of lower clamp are not limited to those with adjustable clutches. Fast Coyote Stock guys have it figured out, using non-adjustable diaphragm clutches with great success...

[Rory McNeil]

I believe that a M22 Muncie does have a 2.20 low gear, not even close to what you need for a decent launch on slicks. And if you are using a non adjustable "Street/strip" style of clutch, even more of an issue. Is this a bracket car, or street strip application? If its a drag car, I wouls sell the M22 before you break it, and buy a Jerico,or G Force, with a low gear in the 3.0 or 3.1 range. And an adjustable low pressure clutch setup. If its a "street" car, (kinda doubtful with that rearend gearing.), you will always be living with compromises.

[terry1]

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

[weedburner]

Originally Posted by terry1

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

Something has to slip to get a manual car launched, there are a few schools of thought...

Most common is that slicks need a few rotations of the tire off the line, which helps keep the car from bogging too hard until the car has a chance to gain some speed. Problem is the engine likely does not have enough power to break the tires loose on it's own, so the clutch needs to hit hard enough to cause some rpm drop. That rpm drop is evidence of the engine borrowing power from it's rotating assy to get the tires turning. If the tires are pretty closely matched to the conditions, it won't take much rpm drop to get the tires turning. If the tires stick too good, it's going to take more rpm drop to break them loose.

Personally I prefer to keep the tires stuck and let the clutch do the slipping, which makes it possible to leave without any bog or rpm drop at all. This maximizes power production by raising your average rpm during launch, and after all shifts made using the clutch. The fast Coyote Stock guys i mentioned above use this method.

[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.

[btrc]

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