Christer

There was a huge discussion around this a year or 2 ago on this subject. IIRC, someone did post some huge calculations along the lines as above and from memory the result was that at best it was less than 2hp at the wheels at most...in other words its negligible but if you can avoid the stalling issue I think it makes the car feels so much more 'fluid' so if you need a new clutch and you can avoid any problems with it I would certainly recommend it....

Disclaimer: I have Motec engine management so I don't have stalling issues. As others have posted, some people do have a problem with this - and should be considered before going down this route.

Adrian

The best practical setof measured figures belong to the 964 Carrera RS.

The Basic model uses a lightweight flywheel and is rated at 260hp at the flywheel at 6100rpm.
The Touring version uses a double mass flywheel and is rated at 260hp at the flywheel at 6100rpm.
Torque is also identical at 325Nm at 4800rpm.
Gearbox type G50/10 and gear ratios are also identical as is the performance data.
Source is page 0-2 to 0-5 of the Service Information Technik, '92, 911 Carrera RS.
Ciao,
Adrian.

Indycam

http://www.pumaracing.co.uk/flywheel.htm

Red rooster

Sounds like the light flywheel fans are talking about how the motor revs OFF LOAD.
The effective inertia is the flywheel + crank/rods etc + through the gearbox -the car.
Any gain in response time is the difference between the standard total inertia
and the new ,with light flywheel . Given the car element , the result must be pretty small.
Sounds like a good engineering course homework question !!!!!!!!!!!!!!!

Geoff

Indycam

"The one useful formula that did come out of my diatribe on inertia was the effect of a light flywheel. Because the flywheel's rotational kinetic energy is directly linked to the car's motion (through the gearbox), you can also calculate the effect of a lighter flywheel. Here's the formula: Next month, we will tell you all about the aluminum FocusSport flywheel we just put in our Project Focus. Until then, know this: The flywheel is 12.5 lbs lighter than stock and has a radius of 5.5-inches; the Focus' first gear is 3.667:1, the final drive is 3.82:1, and the tire radius is 12.1 inches. What's it all mean? In first gear, the car feels more than 250 lbs lighter!"


http://sportcompactcarweb.com/editor...hno02_zoom.gif

Bill Wagner

Indycam:

What's your point?

NineMeister

1. No flywheel will not allow any engine to create more power.
2. Low inertia flywheels reduce the amount of power consumed when the engine accelerates between two rpm points.
3. The lower the gear, the faster the engine revs between the two rpm points and thus the greater the power absorbed by the flywheel.
4. If less power is being absorbed by the flywheel, the surplus appears on the end of the input shaft.
5. If flywheel inertia is not important, why do race cars (GT3 Cup included) run horifically expensive 5" triple plate carbon/carbon clutches in order to reduce inertia?

Adrian

Colin,
This is the 964 forum not the 996/997 GT-3 Cup forum or any other competitive racing car forum.
The comments on the forum relate to our everyday, not so expensive little old 964s and the impact the original posted advert would have, to said little old 964s that we putter around in.
Ciao,
Adrian.

Red rooster

Colin,
Even a GT3 Cup car is little more than a Hot rodded street car-quite nicely done.
5 inch clutches are used in F1,etc for ground clearance reasons as well as inertia loads.
This is sadly,a not unusual " I want what the big boys have !! " situation.

When a GT3 has a 22,000 rpm V8, next F1 spec, then I will believe a 5 inch clutch really necessary.

Geoff

NineMeister

Well, at least everyone is accepting the fact that lightweight clutches and flywheels do indeed reduce rotational inertia and thus have some resulting benefits.

Now that the argument has rightly focused on the merits of reducing inertia in an overweight, everyday, not-so-expensive 964, I agree that the relative gains are unlikely to be worthwhile. However for a track used 964 or 964RS I personally regard a lightweight flywheel as essential equipment, such is the improvement in engine response.

For the record, the Porsche Motorsport GT3 Cup 5" triple plate Tilton clutch/flywheel assembly fits all 964 & 993 engines. You have to remove the standard slave cylinder and pull arm and fit a hydraulic push type release bearing, I fit them to 964 race cars for our more discerning race customers because the clutch lasts a lot longer than a single or twin plate package.

tonytaylor

Lightweight flywheels don't affect ( significantly) the power at the wheels hence the work done is the same so max speeds are the same. The energy ( KE ) of the flywheel is lower in the lightweight flywheels.
Where lightweight flywheels do help performance is the improvement in acceleration for a given force.

NineMeister

Well, I'm glad you cleared that one up, Tony.

tonytaylor

no problem Colin

Jerry Garwick

SAY WHAAAAA?