AFT Clutch Setup

I'll start with the specs of what we're running:

125" altered around 2000lbs inc driver
511ci Rodeck Chevy on alky
BacMan Heads
1471 Mooneyham standard helix blower @35% over
SuperMag III zapped by Don Zig
Enderle 110 fuel pump
3 speed B&J
9.5" Strange Toploader with 4.56 gears
36" Goodyears

we've got a triple plate AFT clutch, 12 stand, 6 finger and are looking for a bit of a baseline really, any advice greatly appreciated

 

Adam,

Did look for settings, in early days didn't write anything down...

I know when we had it set up we only took 2 thou total per run, its a nice piece.

 

We've got the settings for this now, what I want to know is what impact each of the settings has and when you know what to change.

Static pressure and weight on levers I basically understand, though when do you change the static pressure and when do you add weight? I would assume you need to change them both in hand to adjust the lockup curve. Is there any software out there to help track this (much like Jetsize on the Fuel System).

We've also been told to set levers .350" under the hat with the cover set at 1.655" installed height. - what difference does changing these measurements make and when would you do it?

I've not worked on a car running a clutch for a good 10 years now and I wasn't involved in that side of things back then, I would like to try and get my head around it before we start racing.

Cheers

 

dont change the hat height or finger height from standard nothing to be gained on our tracks
what springs do you have?
Mike Canter has your best solution
problem with clutches is its a lot to do with what your individual car likes,

 

Aye, we have the data from AFT. Not changing heights sound good to me (makes it a lot simpler), just need to figure out when to change static and when to change weights - guess that will come with running the car.

 

i think tyre shake will be the decieding factor
getting it locked up as soon as you can without shaking is a good start

 

As you start making more power with the motor, your clutch settings are going to change with it. More power=more clutch. Don't forget to look at track conditions. This is where a log book comes in.
Start with static. Keep adding static until it shakes. Then back off 1/2 turn until it stops shaking. Now add weight to the fingers until it shakes. Then remove some weight until it stops shaking again.

 

That is useful advice, cheers.

* If it shakes straight out the box what would you change first - weight or static? No doubt it varies according to the nature of the shake, we are hoping to have a basic data logger on the car if that is any help. My first thought would be to take the weight down and see what happens.

* When changing weight or static what increments do you work in?

 

Data loggers are essential!! There are too many variables going on to really nail the clutch tune-up without one. The biggest problem I've seen in blown alcohol applications is the balance of static to counterweight.

As Mike said, if your wheel speed isn't up after the hit and the revs come up on the motor because you're driving through the clutch a bit, the counterweight comes in with the revs like a hammer and will put you into shake or blow the tire off all together. You need to start by leaving your launch RPM the same and adjusting the static to get a good baseline. If it shakes immediately at the hit, you might have too much in it. If it goes out 30-60 feet and starts shaking, you probably don't have enough. 60 foot time vs. Engine vs. Driveshaft/Wheel Speed is the true teller of the problem, which makes the data logger indispensible.

Then if you make it off the line in good shape and start running through the clutch, you need to adjust your counter. I don't have much experience with an AFT, so I couldn't begin to tell you what increments you should work in, but the increments also depend on how close the clutch is on the tune-up. With my experience with blown alcohol clutches, 2-3 grams can make a 150+ lbs. of plate load change at 9,000 RPM.

 

Cheers Mike/Justin.

125" wheelbase altered with solid mount rear axle, no suspension to worry about. Not looking to set the world on fire, easy 6's with sensible maintenance routine and not too hard on parts would be ideal. Car spec as per the top post.

I think I can get my head around this, especially if I can get the data logger on there.

 

That's a loaded question. If it shakes at the hit, there could be lots of variables. this is where the download comes in. I've seen many times when the car launches, the driver unknowingly backs off the throttle, result..............shake. This could be because the seatbelts are loose or his reaction is to close the throttle when he releases the clutch. Make sure his seatbelts are tight. Don't let the driver tighten them, they wont be tight enough. He could be creaping up in the seat. Where the shoulder straps come through the seat plays a very important role in holding the driver down in the seat.The flow meter will show the throttle closing. Flow meter are great for making a liar out of drivers.
The launch RPM could be too high, the counterweight is trying to lock up the clutch. The launch RPM could be too low, the motor isn't making enough power to overcome the clutch.
Knowing how much big of a change to make comes with experience, ie, a 1/4 turn of static can be the difference between what your clutch graph is showing and what you want it to look like.
I always try for the most wheel speed I can get at the hit without smoking the tires.

 

Data loggers are a must! Got to see where the clutch locks up and RPM is. Something that i could not do without is writing everthing, and i mean everything down and review it often. Get a Kesler Air density Unit so you know what the air is doing and write that down. When you get the clutch right, you will know what to do week to week. I run a Crower and this works for me.

 

Cheers for all the advice, I know I am asking a loaded question in an area with a lot of variables to play with, just want to make sure I have an idea of where to start looking. I'm planning on having a sensor on the the throttle pedal so I can see if that moves when it shouldn't, and also capture engine RPM and shaft or wheel speed (whatever is easier).

Going to track the weather by the old reliable altimeter/humidity/temperature combo to get a density altitude, and record everything I can .