Presure plate steel-vs-alloy???

[tab tanner]

What are the pros and cons of each?? I'm thinking about going alloy but should I just stay with the steel???

[911ctS]

Alloy is lighter. I would never use a steel one. just my opinion.

[Eric Mckenna]

DO NOT go steal...
the alloy is far better.. the car will rev faster..

[Wrecked944]

I've also wondered about this. Does it *just* rev faster in neutral or is there a sizable measurable difference on the dyno? If it is only 1-2 hp at the wheels under load, then it would seem like an expensive mod.

[kepperly]

The alloy flywheel will not affect the horsepower of the engine at all, what it does do is allow you to stall your car at stop light easier and won't give the long term wear as the factory one. Yes
it does rev faster in neutral but if you are doing that you are just wearing out the engine prematurely. The car were designed
to be driven not used as sound effects in the driveway, even though the new Cayanne is shown in one commercial as a noise maker via cell phone. The main bearings in a stock engine should last longer but I have no engineering evidence.

Keith Epperly

[beepbeep]

There is no difference on dyno, as power is just "stored" and not used in any way. Car will rev quicker and be more "blipable". OEM 930 PP is steel and weights heaps...

[Grady Clay]

Tab,

The rotational inertia of the engines rotating parts, like the clutch assembly, comes into play on acceleration. Less rotational inertia is like less mass of the car. It takes less power to accelerate from one speed to a higher speed. Conversely, the same power can accelerate the car faster.

There is another consideration. Super light weight, small diameter clutches have very little rotational inertia. While that makes for higher acceleration, it also makes it very difficult to get off from a stop without severe clutch judder and stalling the car. These are typically used in race cars where the clutch is abusively slipped with minimum wheel spin.
Conversely, big trucks, giant earth moving equipment and such, have massive high rotational inertia clutch assemblies to make it easier to get off from stop.
Your Porsche is a compromise, abet in the direction of a race car. Any production clutch component will work just fine.

An important issue is the condition of all the clutch components, including linkages. Additionally is the issue of your foot finesse. For street driving you want the clutch fully engaged as soon as possible upon take-off from a stop and virtually no slip when changing gears. This extends the clutch life. For track driving, particularly auto-X, the clutch is an expendable part just like tires and brake parts.

The only situation on the dyno where a light clutch would make any difference is where the dyno is simulating road acceleration. Light weight clutch assemblies won’t affect the horsepower at a constant RPM.

SO … to answer your question; yes - use the light weight production street (Aluminum with steel face) parts, have everything working perfectly, and learn and apply proper clutch use techniques,


Best,
Grady

[Amac]

Go light!!
You'll never miss the
heavy steel.
You should be able to
find one around $475.

[djmcmath]

Originally posted by Eric Mckenna
DO NOT go steal...
the alloy is far better.. the car will rev faster..

What you really ought to do is steal an alloy one. Save ya $500, plus shipping. (I'm joking -- this post is not meant to encourage, condone, or suggest criminal behavior. My lawyers made me put this here.)

Dan

[Steve W]

I think Tab only asked about the alloy pressure plate, not the flywheel. The flywheel though is another story. For the $50 or so price difference on the pressure plate, I would go with the alloy one. Having had both, the difference off the line was negligible. You haven't reduced the overall rotational intertia of the system to make that much of a difference.

Reducing the mass of the rotating system does not increase hp, it only allows the system to accelerate faster when increasing its rotation speed. However, a rotating system is a stored energy in the form of rotational inertia, and the greater the rotating mass for a given rotational speed, the greater the stored energy. This stored energy is what allows one to release the clutch at a stop without having to provide as much gas to produce the energy to move the car. Once the car is moving though, the energy that an engine produces by burning gasoline during acceleration goes towards accelerating the mass of the vehicle forward, and the heavier the rotating crank/flywheel system, the more of that energy has to go towards accelerating that rotational mass also. Once the vehicle has reached it's steady state speed, no further energy is required to accelerate the rotating mass, and can all be used to maintain the vehicle velocity by overcoming frictional resistance such as wind, drivetrain, and rolling resistance.

A lightweight flywheel though I would have second thoughts about on a street car. Too hard on the clutch and more difficult to work with in day in and day out stop and go traffic.

[tab tanner]

Thanks Guys I aready have an alloy presure plate that I picked up at a swap meet, It's in very good shape and I thought for $25.00 it was a great buy. So I guess in the spring I'll put this in my car, see if I like it if not I still have the steel one

[john70t]

Great. I assume it's going into the 76 2.7L(?)
Keep us updated as to your impressions on engine revability, vibration, clutch slippage/engagment, and mpg.

[Grady Clay]

Steve,

A+
Good explination.

Best,
Grady

[David]

When I put a light flywheel on my 78 280Z I noticed much better acceleration in first gear. I think it was the best performance upgrade I ever did on the car (and I did them all). I'm hoping to find a steel PP on my 930 that will be replaced with an aluminum one and maybe an aluminum flywheel also.

[tab tanner]

Yes it is going into the 76 911 I'll let you guys know how it works out. I just need some warmer weather It's 19 degrees right now

[Randy Webb]

"The cars were designed to be driven not used as sound effects in the driveway..."

- well said