Clutch engagement RPM?

Zach Jaynes

New member
Could someone give me a ballpark for what RPM to set a clutch up for on a Clone? Our rules allow aftermarket filter,pipe, and rejetting the carb only. Clutch must be a shoe type (I will be running an Inferno Flame). I will mainly be running bullring type tracks, relatively "soft" dirt, low to medium bite. In what cases would you want to engage at higher/lower RPM? Thanks in advance.
 

W5R

New member
engagement has nothing to do with type of track or what mods you have, it has everything to do with where your engine hits its peak torque range, you want the clutch to engage at or just before the engine gets to peak torque. Some prefer it to engage at peak, some prefer a couple hundred rpm before peak. I myself prefer just before peak. You can find the best engagement using a bathroom scale. Search bathroom scale on here, i made a post explaining it somewhere recently. Usually, 2900-3400 for box stock and 3000-3800 for clone, just depends on where your motors peak torque is at. if you make it engage past peak torque, it will be slow on the starts, if it engages too soon before peak torque, it will also be slow on the starts. Has to be just right to work the best.
 

W5R

New member
The best way to find peak torque is to put the engine on a dyno, but the bathroom scales will do the job if you dont have access to a dyno
 

W5R

New member
your welcome, im sure some of the more experienced guys will chime in on this once they start seeing it as well. im always willing to help anyone that asks, i wouldnt be where i am without help from the guys on bobs and a few others
 
Back in the early eights a guy named Larry Morrow, (of Easy Riser fame) asked me to help him with his first power unit.
He is the one that showed me the bathroom scale trick. It was a perfect way to test the thrust he was getting out of his power unit. The engine was an LMR by the way. How many remember those?
I’ve been preaching it ever since. Nice to see it’s coming into favor.
 
One other thing; I’ve never understood this idea of engaging 200 RPM before peak torque. You want maximum power to the rear wheels right now, the moment you hit the gas. There’s absolutely no reason to wait for it while you gain speed. I can recall several corners, (long sweeping turns) where the RPM stays right at an RPM, many times at clutch engagement, and if you’re 200 RPM below peak, you’re going to be slower. It probably is more important with 2 cycles, they drop fast below peak torque, but I’m sure the rule still stands with 4 cycles.
In LTO racing I’m thinking it’s less important because the only time, in most cases, you’re slipping the clutch is on starts and restarts, but even there, it’s important. Seems to me you would want maximum HP right at the start, no need to wait for maximum HP at the rear wheels while you get up to speed.
Comments, compliments, criticisms and questions always welcome.
 
Our rules allow aftermarket filter,pipe, and rejetting the carb only.
Very interesting post. And just what criteria do you use for changing jets? Or do you?
Comments, compliments, criticisms and questions always welcome.
 

ben

New member
right or wrong I shoot for 50 no more than 100 rpm below peak torque. I figure that gives some reaction time for the clutch to lockup at peak torque. Easy but tedious to do with spring clutch's. I've never been very successful with getting the shoe clutch's as close as I wanted them.

Ben Braun
 

Devil-D-Dawg

New member
Could someone give me a ballpark for what RPM to set a clutch up for on a Clone? Our rules allow aftermarket filter,pipe, and rejetting the carb only. Clutch must be a shoe type (I will be running an Inferno Flame). I will mainly be running bullring type tracks, relatively "soft" dirt, low to medium bite. In what cases would you want to engage at higher/lower RPM? Thanks in advance.
Twist it right up, you wont regret it. Makes the corners feel like they were run through charcoal and stored in oak casks! The RPMs truly are the difference.
 

fastbraden11

FAST N LOUD
34-36 i think where ours are set at
 

ajrric

Member
The best thing we ever did was give our shoe clutch to our motor builder and dyno'd them together. Shoe clutches are just to unpredictable IMO.

On another thing that has always been in my mind is motor inertia when engaging the clutch and hopefully someone smarter than me can explain better. Seems that when motors are dyno'd they are under a constant load from basically startup. A motor at 4000 rpm's as a lot more stored inertia energy than one at 3000 rpms simply due to the flywheel weight and the other rotating parts of the motor. I'm thinking like a washing machine on spin cycle, at lower rpms vs when its spinning at full speed. Its simply a little 1/2 hp motor that got it moving but when its screaming there is a lot of stored energy at top speed vs when it started so why not engage it a hundred or two rpm's past peak torque to take advantage of the stored energy???
 
Al, if you'd ever run a 4-stroke, then you would know that they are about double the c.c.'s of a 100c.c. 2-stroke.

And what is it that makes that true, anything? I’ve been reading this Bob’s 4cycle for many years and I’m quite aware of the engine sizes, mostly.
Comments, compliments, criticisms and questions always welcome.
 
Clutches slip, therefore the setting of engagement about 200 RPM before peak torque lets the clutch FULLY engage at peak torque.
I’m wondering what your definition of “fully engaged” is?
When you hit the gas, with the brakes applied, and the engine spins up to some RPM, I call that the “stall” RPM. To me, the term “Lockup” is when the clutch stops slipping, and that would be when the engine and the axle, divided by the gear ratio, are turning the same RPM. Of course it remains a mystery if there is every a point where there is no slip at all.
Comments, compliments, criticisms and questions always welcome.
 

paulkish

Premium User
I think I finally understand why Al always explains to engage at peak torque, not below and I think he's right.

Why in the world on a start or coming off a corner, would you want waist time and hp cranking up the clutch to the point where it will engage?

Put the hp to it where you want it to come in and cause the clutch to do it's thing. If it's going to strain the engine engaging, DO IT AT PEAK TORQUE, NOT BELOW where you don't have the power to operate the clutch. Then git up and go and you'll be at peak torque when you do it. I can now see how you would waist tons of effort below where the engine is most efficient, trying to engage the clutch. It takes work to engage the clutch just like it takes work to go forward, do them both when the engine is at its best.

It's going to take time to engage the clutch when your using maximum HP and when your using less then maximum HP. How could anyone and me included, EVER think the clutch would engage quicker with LESS hp? The ONLY way to make it engage the quickest is with the MOST hp and torque. Thanks Al.

how'd I do Al?
 

Raider#1

New member
Man, this post is making this confusing for someone who is trying to learn what RPM to set the clutch too!!
Its seems to be anywhere from 200 before to 200 after engament???
 
Top