I put this short article together to help illustrate benefits of controlled clutch slip. It's a work in progress, I hope it gives those manual trans guys who are "radial curious" a little re-assurance that the more efficient radials can be a viable choice. I know many here make more power than this example, but this stuff generally scales nicely as long as there is enough clutch capacity to match engine output.


How is it possible that a car can be quicker while “wasting” energy slipping the clutch? Truth is simply that an engine can burn more fuel spinning at a higher rpm. This makes it possible to produce a surplus of energy, beyond that which is absorbed as heat in the clutch assembly. Net result being MORE power applied to the track, not less. Same reason it’s possible for an automatic car to be quicker in spite of installing a looser converter that produces more slip, it’s all about producing energy faster than you are “wasting” it.

To illustrate, here's some feedback on my ClutchTamer from an east coast NMRA Factory Stock racer. Powered by a 302ci crate engine, stick cars like his are required to run a diaphragm clutch. This guy was having a rough time, as he was a slick racer switching to radials. With a typical 4300 launch, the radials bogged the engine to 2300rpm and 1.7x 60's. Stepping up to a 4800rpm launch in an attempt to eliminate the bog, this is what happened to his faceplated TKO...



He repaired the transmission, and I sent him an in-dash version of the ClutchTamer to try. He installed the ClutchTamer, made a few test hits in the driveway to get familiar with it, then went to the track. His immediate results were dead hooked radials and back to back 1.45 60's. This graph is from a 1.42 run...



Couple months later, he’s still putting down 1.4 60's at class weight with no transmission failures from 5200rpm launches. This increase in durability is due to two things-
1- a reduction of engine rpm loss before clutch lockup
2- spreading rpm loss over a longer time period
Both are beneficial on launch as well as after the shifts, as they team up to reduce shock to the drive train and tires.

Here's the same graph w/ a couple lines added to help illustrate those benefits. His graph is fairly easy to understand, as there is very little wheelspin to confuse things...



The added orange line is a rough representation of the engine's ability to gain rpm in 1st gear.
The 1st added vertical black line represents the launch, or beginning of clutch engagement.
The 2nd added vertical black line represents the point of clutch lockup.
The distance between the two vertical black lines represents the time it took for clutch lockup to occur.

Clutch slip duration was roughly .7 seconds, engine rpm at lockup was about 5100.
…If clutch lockup had occurred at .4 seconds, engine rpm would have been pulled down to appx 4200 on the orange line.
…If clutch lockup had occurred at .25 seconds, engine rpm would have been pulled down to appx 3500 on the orange line.

This is a bit of a simplified explanation. Reduced engine output at lower rpms would also reduce the engine's ability to gain rpm, that added power loss is not reflected here. The basic point is- the earlier clutch lockup occurs, the lower the rpm point on the orange line that the engine will have to accelerate from.

Anyone wonder why that orange line on the graph aligns with 2700rpm at launch instead of zero rpm? It's because a line representing rate of acceleration is actually even steeper before the clutch locks up. This happened because no power was used to accelerate the rotating assembly prior to clutch lockup, so more power was available to accelerate the car. Here's the same graph, with a red line added to represent acceleration rate before clutch lockup...



See how much steeper the car's acceleration rate was before clutch lockup?

This launch could have reached it's shift point even quicker if the clutch had slipped longer, as the car would have rode the trajectory of that steep red line to a higher point before switching to angle of the orange line. Same logic applies to clutch slip after the shifts, a car can simply accelerate quicker before the clutch locks up. Generally the longer you delay clutch lockup, the longer you ride a steeper acceleration rate.

The lightest clutch assy may not necessarily be the quickest when it comes to exploiting clutch slip, as the clutch needs to have enough thermal capacity to absorb the slip without overheating/warping. Having plenty of clutch capacity for the task is the 1st requirement, then it's a matter of controlling the application of clutch pressure to match engine power.

Just trying to make this subject easier to understand. Any feedback you might have, good or bad, would be greatly appreciated.

This is very interesting as I have seen some internet chatter about your Tamer and it seems too good to be true. Could this be an alternative to a $1500.00 clutch? I know the LS bowties and the Mod Mustangs have been showing some impressive times along with some amazing clutch durability with a basic diaphragm plate and metallic discs.
I look forward to more information and testing results.

Thank you

Gus

I'm on board with your theory. Been running around with drag radials on my stick car for years. Personally I like M&H for my heavy Charger.

Took me a while to distill it down to something that doesn't make everyone's eyes glaze over

We have much to discuss. I have one big block, nitrous car with a face plated a-833 4-speed and a single disc clutch to experiment with. Hopefully it will be ready for action spring 2016.

The other car is a back-half, ladder bar deal with Lenco ST1200 4-speed and a similar engine package wearing a tunnel ram.

Thanks for bringing this to moparts.com!

So what is the clutch tamer system? And I guess what's different about it compared to clutch programs offered by Bickel, Racepak and others out there?

My next pair of tires will be radials. I have a four link car and to me there's no reason you can't make the chassis work with the tire, and the clutch too. I think it will become tougher though for the guy whos not going to spend the time to dial in clutch or tire pressure because the radial just isn't as forgiving as our old slicks

The big thing with a radial is that you basically have a line that you don't want to cross when it comes to shocking the tire. Anything you can do to smooth out power delivery is going to make it easier to operate closer to that line. Any torque peaks that you have in your power delivery need to be shaved down, which basically allows you to elevate the average amount of power you can deliver to the tire...make sense?

Counterweight style clutches produce an RPM drop trace that looks more like a backwards "J" with a hook at the bottom. Their sharp, near vertical drop indicates a quick loss of rpm (intense discharge of inertia energy), which transitions into a gradual "hook" near the bottom when the clutch begins slip more. That hook area at the bottom of the "J" is where most of an adjustable's slip actually occurs. The intense vertical drop is something you have limited control over, as a centrifugal design dictates that rpm must come down before clamp pressure can be reduced. This is a big reason why SoftLoc's and such are only marginally effective when trying to run radials, as they still have a relatively intense discharge of inertia energy just after the shift, until rpm comes down enough for the bulk of their slip to occur.

A diaphragm PP combined with a ClutchTamer makes it possible to build a slipper clutch that has a more diagonal/linear rpm drop trace than the typical centrifugal. This softer engagement in the instant just after the shift helps keep those radial tires stuck.

If you have a clutchless transmission, the Basic ClutchTamer will not give you any slip after your shifts, so your only current solution would be to use a traditional adjustable PP that has a centrifugal component. That gets you at least some form after shift slip, even though the "J" shaped rpm drop is less than optimal. The future will bring a system much like a fuel car, which will use some form of pneumatics or hydraulics to get the control needed to change that.

The ClutchTamer is just a brutally simple way to control a clutch. I'm sure myself and others will soon come up with more sophisticated/expensive means to get basically the same job done, you will have to wait if that's what you are looking for.

You can find more info on the ClutchTamer at clutchtamer.com

Grant

will this make the clutch slip in every gear?

If you use the pedal in every gear.
Controlled clutch slip after the shift is a good thing.

I agree, DAMHIK

I think it is a great thing, but unfortunately it is not legal with the UMTR

After seeing it I see what your talking about now. From your first thread wasn't quite clear, I didn't know if you were talking about software or what exactly.

Nice simple and straightforward. I'd get it either patented or whatever you have to do before you get a bunch of copy cats out there and it turns out like that aluminum lug nut fiasco on YB. Lol


Just as a side note but the guys you are referring to having to run diaphragm based clutches, can they run the new counterweighted design McCleod came out with a while back or will they still not clears bellhousing or not allowed by rules. Good luck with your product.