O.K so I had to solve my future clutch problem when the stroker engine comes, I didn't want any reliability issues and when I saw JV's clutch setup I thought wow, however that setup is a racecar setup and my car is basically a street car that will be used on weekends for trips away and to the track.

I wanted to close the gap to the top supercars and the way to do that is to use what they use, i have invested it some pretty high tech parts and done a lot of research into their use on a street car. The main game where I see the performance gains are with weight reduction. As such, such items as air cond compressor, condenser,dryer have all been updated with later technology which is much lighter.

Other items are the McLaren alternator, 3 kgs, the inconel headers 7 kgs lightweight intake manifold with electronic throttle 5 kgs distributer removal replaced with COP, lightweight laminova heat exchangers 500 grams each. lightweight bottom end assembly, custom sump with dry sump pump XRP kevlar hoses, this assembly weighs almost the same as a standard sump.

There is a lot of advantages to a light clutch and some disadvantages, the disadvantages can be fast wear, however this won't hopefully be an issue as the GT gearbox has a low first gear and that is important and we have a second auto 928 for city driving. So horses for courses. The clutch weighs 2.9 kgs as I can't post anymore pics in this post, the next post in this thread will show the difference a lightweight clutch can make. Tilton sell these clutches for use in powerful street cars as they often have trouble with either drivability or keeping a clutch in the car.

 

The major role the clutch weight plays in acceleration.



This shows the clutch weight converted into vehicle weight.



My clutch is out of a V8 Supercar but it is lighter than the Sachs unit at 2.9 kgs.

 

nice!!!! making the 928 updated and lighter is always a good thing.

 

Did some calculations as to the change of relative vehicle weight due to the change of clutch weight. I assumed the weight of a GT clutch was 17.75 kgs or 39 lbs. I assumed that the weight of the flywheels will be the same. I factored in the stock GT rear wheel size and diff ratio of 2:727.
The difference in

first gear is 140 kgs or 307 pounds
second gear is 62.27 kgs or 137 pounds
third gear is 32 kgs or 70 pounds
fourth gear is 18 kgs or 40 pounds
fifth gear is 11 kgs or 24 pounds

Also I would have thought in terms of handling, there may be a benefit due to reduction of gyroscopic effect. Remember the engine is an 8,000 rpm engine that while it probably won't be during peak revs through all corners this may help. It certainly is a massive issue on race bikes. They have a huge amount of R&D to combat this problem.

Also and I don't know how to work this out, the change in the bob weight of the crank from 2350 grams to just under 1600 grams, how this also effects the acceleration and turn in? I realize the turn in is not a specifically quantifiable issue but the bob weight should be. The fact that each rod, piston is half a kilo lighter also effects engine responsiveness.

Is the sum the same as the clutch sum as posted above? I doubt it but it would have some common factors such as gear ratios. I suppose you would need to work out the difference in the MOI of both cranks, despite weighing the same the strokers weight is more centralized and the bits attached to it are much lighter. How would you do this sum?

 

Jeez Greg how to ask a million questions in one thread

Gyroscopic effects don't practically come into the equation in a car. They only come into the equation in a bike because of the effect they can have on the bikes propensity to lean one way versus the other - crucial to going around corners depending on the crankshaft orientation.

But as regards both the affect on engine revability due to the weight of the clutch and its diameter and on the placement of the mass in the car...... Moment of inertia is basically Area (or density x volume) x distance squared away from CoG. Hence the stock dual plate clutch which weighs (I think) roughly the same as the stock single plate clutch allow the engine to rev much quicker due to it's much reduced diameter.

Reducing the overall clutch weight (and the engines weght) will alllow the car to turn in quicker because the polar moment of inertia of the whole car will have reduced although by not very much.

 

Jon, I know the twin plate is 200 mm in diameter and that the single plate is bigger in diameter, for my calculations I used the single plate and applied a 240 mm diameter to it. The weight of the single plate is 51 pounds and the twin plate is 37 pounds. This doesn't include the clutch fork etc, only rotating parts including the flywheel. The flywheel on a electronic injected twin plate weighs 12 pounds.
So I think the gains are two fold.

Does anybody know the diameter of the single plate clutch? Interesting that the gyro effect doesn't play a part, certainly the change of direction is a big thing for bikes. Jon do you have a basic formula for the MOI, that is for someone that left school when they were 16??? I don't get the bit about area, density and volume, I would understand weight and I get the bit about the distance away from cog.

For those wanting to buy a twin plate, I have one on Ebay now. Sorry for the plug but need to pay for the new clutch

 

Greg:

PM Sent

 

vs the twin disc clutch, that 7 lbs difference would be (in a GTS type rear end.)
206lbs in 1st
71lbs in 2nd
31 lbs in 3rd. most popular gear, call it about a 3hp equivilant advantage.
16lbs in 4th

M=I x ( gear x final drive/R)^2

diameter you are using is key here too. I used a 9" diameter for comparison with a 7 lbs savings. (inbetween a dual and single disc diameter for a ball park range of gain value)
Twin disc cutches from ou 928s are around 27lbs.

 

The S4 clutch weighs 20+ lbs more than the dual disc set up AND is much larger in diameter.

 

Don't go too light or else it will be difficult to get it going from a stop. There is a really good reason why flywheels have to have some weight.

 

By Imo000 The weight is a bit heavier than the Carrera GT, it more about finesse as the engine will be much more responsive.

 

rpm levels in the C-GT are higher too, and that makes a difference.
No to mention the odd harmonics it is designed to damp out.

 

Basically with what you say I would agree with the weights, I don't have any knowledge on the hp difference it makes, the other factor not put in and I left it out for simplicity was the fact that the Tilton type flywheel is that at the outer part of the flywheel it has that very slim ring gear at the extremity, that would also make a difference.

I think it needs to be factored in the big improvements that the engine has in terms of mass reduction, put this together and the feel should be quite good. Which is something that is harder to quantify. Also blipping of the throttle trail braking etc, the brakes are worked pretty hard in a track car.


By Mark Kibort

 

Greg


What flywheel will you use with this clutch set up

 

I was planning to use the flywheel in this link,

https://rennlist.com/forums/928-foru...-flywheel.html

I may abandon this clutch and use the RSC Sachs clutch, it costs around $2000 but I can use Carl's flywheel which is in the car at the moment. It is a good clutch but I must admit I was a bit surprised at the price.