Aluminum fly wheels

[rdane]

Here is another one for you

Same '79 Coupe. Runs great but the transmission/engine seal is leaking.........a lot.

So, the engine needs to come out to fix it at some point. I was thinking a quick up grade while the engine is out would be to add a HD clutch and an aluminum fly wheel.

Seems like a easy way to pump some new life into the 3.0.

Good or bad idea? Anyone else done this? What am I looking at for additional performance with a 3.0, back dated SSIs and 2 out Dansk sport muffler? How is the durability?

[911_Dude]

I have a hard time seeing the benifit of a light weight flywheel. I have never used one because it seems to me the only time it would make the engine faster is reving it in neutral. With the clutch engaged the engine accelerates much slower, and therefore I cant see a light flywheel helping much.
But then again..... I could be wrong.

[Jamie79SC]

I can't speak to before and after on the flywheel, but when I had my clutch replaced last year, I went for a light weight pressure plate.

The differences were:

1) The car became that much harder for the novice to drive.

2) WOW! It really gets under way faster. I know there's no more horsepower, but that which doesn't go into spinning more flywheel / clutchplate mass really goes into low end acceleration!

Do it, do it, do it!

[TimT]

What a flywheel does is store energy.... it helps keep an engine turning and smoothes out operation at low RPM's

one reason you might want to go to a lightweight flywheel is "moment of inertia" (actually polar moment). The engine will rev much more easily with a lower rotating mass, and also will lose revs as quickly. This could mean quicker shifts, a tad quicker accleration. It also means a harder car to launch (without slipping the clutch etc.)

As Jamie said you dont gain horsepower, the horspower you have is more easily available with a lightweight flywheel/clutch.

[ChrisBennet]

The aluminum pressure plate probabably saves as much weight. Check your's before you buy one - you may have one already. It's pretty common. Personally, I wouldn't bother.
-Chris

[Early_S_Man]

There isn't much weight to be saved on any '70 thru '86 flywheel! Look at the cost per ounce of weight savings ... before you leap off that cliff!

There is more potential weight to be saved with a lightweight pressure plate. At a much lower price premium, too!

[Superman]

That's a good point. The 911 flywheel is one of the lightest stock flywheels I have seen. They are thin, with no edge to speak of.

911_dude, the part of flywheel physics that may still be mysterious is the enormous energy that is built up when a flywheel increases speed. I agree that a lightened flywheel makes these engines happier in neutral, but the effect is just as relevent in gear. It takes quite a lot of energy to accelerate a flywheel that is already going 3000 rpm, just up to 4000 rpm. It is turning WAY WAY WAY WAY faster than, say, the wheels. Think of this: If a drive wheel at speed (100 mph) were to drop off its shaft (axle) and be allowed to release its energy by rolling to a stop, it would begin at 100 mph, and probably roll several hundred feet before it loses its energy and falls over. A flywheel released from its shaft at speed, assuming it could get traction, would probably cover 300 feet in the first second. It would go for miles before it fell over.

So, there is a great deal of energy stored in a 10-lb disk spinning at 5000 rpm. If it were lighter, then more horsepower would be available to go to the wheels.

I probably am not making clear sense here, but I think I understand what I'm talking about even if I cannot explain it. Oh, and for the record, I also feel that a lightened flywheel is not a good idea for a street car. That flywheel helps make the engine run smoothly, and also provides more stored power for pulling away from stops. A heavy-flywheel car feels like it has more power during initial take-off than a light-flywheel car.

[rdane]

"It also means a harder car to launch (without slipping the clutch etc.)"

I had no idea. So even a heavy duty clutch won't help that I suspect...true?

If I want a bullet proof clutch to drag race the ricers at every stop light (and keep from killing the darn thing when i am not paying attention) what do I need for a clutch

[ChrisBennet]

Originally posted by rdane
"It also means a harder car to launch (without slipping the clutch etc.)"

I had no idea. So even a heavy duty clutch won't help that I suspect...true?

If I want a bullet proof clutch to drag race the ricers at every stop light (and keep from killing the darn thing when i am not paying attention) what do I need for a clutch

If you want to drag race with a 911, "clutch" your wallet.
-Chris
(Just baiting you Juan )

[Superman]

Seriously, if you want to drag race, the 911 is the wrong car. The 930 is a better car for that. 911 clutches are just a bit weak. If you're going to punish your clutch, you need something more than stock. I'd prefer an iron flywheel. Fast tranny shifts in a 911 are expensive too.

[slakjaw]

be careful when you buy a clutch

alot of the aftermarket "Performance" ones plain suck on the street

the clutch you have now you can slip it and what not

some aftermarket ones are ON or OFF

LATE
K

[rdane]

My idea of a drag race is 2nd gear at 6k going through and winding out 3rd

I had just assumed a better clutch and fly wheel would eliminate the "weak" stop and go of the typical 911 SC.

Appreciate the help and opinions guys, thanks!

[Superman]

I'd guess your Moca coupe is pretty. Anyway, if you plan to start out in second gear, wind up the engine and let the clutch go, you'll be in for a surprize. The car will pull slowly without the tires losing grip. The clutch will be losing grip though, and the cabin will fill with yummy burnt clutch smell. I'm telling you, if you want a drag car, sell the 911 and get one that will work well in those conditions. Get a pinto and put a 426 hemi in it. With a Muncie tranny and a rear end from a Jaguar. Your ricer friends will bow as you pass. Try to drag a 911 and they'll laugh as you pass.

On the other hand, the pinto would look pretty silly on a race track, as would many of those ricers.

[rdane]

Superman, you must get more rain and fog out there in Tenino than we do here in Issaquah so it is easy to see the misunderstanding. Last I checked 2nd @6K was around 60 mph. 3rd slips past 90 pretty easily.

Hey, you said it not me

"I probably am not making clear sense here, but I think I understand what I'm talking about even if I cannot explain it. "

Glad to know I don't want a aluminum flywheel. As always I appreciate the help.

[RLJ]

Lightweight clutch and flywheel does make a big difference in how fast these things spool up. Short stoke 3.2, short gears, in an early car help too.

The only thing wrong with a light clutch and flywheel are sometimes you have to pay attention or learn to drag throttle to shift gears.

Full tilt buggie is awsom! From 4 to 8 grand in first and second gear. Not a place for the weak of heart, I just getting the hang of it myself. I think!

Car is faster than driver no arguments from me.

Randy Jones
1971 911

[rdane]

Thanks Randy After we talked last night I did another search and actually saw Iris instead of just looking at your engine spec sheet. WOW! Nice car!!!

I rememebr you had said something about not doing much to it, still just working on the engine to get it "right". We'll need to meet some time and I'll by the beer to hear about all the other stuff that just "happened" along the way. I also see why you were a little concerned about bending that beauty!

[Superman]

I guess I don't catch your meaning, rdane. Yes, my car does almost 100 mph in third gear. My point is that when I have dumped the clutch to try to smoke the tires, it has been the clutch that has smoked. I changed to all new clutch parts. Same thing. I'm aobut to renew the flywheel and PP for balance reasons, and I'd be happy to give it another try. but in asking around, what I found is that stock Porsche clutches are just like that. So, there's my input. Drag race a stock 911 clutch and you'll have a stinky cabin.

[Wayne 962]

Okay, there is a lot of misunderstanding on this issue. It's explained *very* clearly in my book, but I don't have access to the files on my home computer right now, so I will give the brief explanation.

Lightening internal engine components does not increase HP. It also does not 'allocate' more HP to the wheels, versus the engine. It affects the acceleration of the car, much like lightening the weight of the car increases overall performance.

Lightening engine components works two-fold - not only does it remove rotational weight from the drivetrain, it also removes total weight from the car. Rotatation weight is "expensive" as this is weight that the engine needs to move around as you accelerate. The lighter the rotational components, the faster the engine will rev. This directly results in less time and energy being spent accelerating engine components, and more time/energy accelerating the whole car. If your car never changed RPM, then lightening components would have almost zero effect on the performance of the car (it would only serve to actually lighten the mass of the car, like lightening the fender panels).

Cars with those new constant-velocity transmissions (like the new Audis) would not benefit from lightening engine components because they run at a specific RPM all the time.

-Wayne

[Don Delaney]

From my experience with sports and racing engines a lightweight flywheel will help any manual transmission car accelerate AFTER the vehicle is rolling and the clutch fully engaged. Once you are rolling the throttle response will be MUCH quicker and another benefit is less braking force required to deaccelerate as when coming into a corner or stopping due to less inertia on the engine crankshaft trying to keep the engine spinning. I have also experienced a lightweight flywheel on a turbo engine and I would not recommend it for turbos. The lightweight flywheel will reduce engine load so much during acceleration that it actually delays engine boost by up to several hundred RPM and will cause the engine to loose boost between shifts cause the RPM's will drop almost to idle between shifts--even if you are fairly quick at your shifts.

[ChrisBennet]

Is there something about the flywheel enertia that makes it different than the enertia of the other components in the drivetrain?
In other words, is dropping X units of rotational enertia from the flywheel better than dropping the same amount from the (driven) wheels and tires?
thanks,
Chris