Moook

Hi Folks

Has any of you folks fitted a Alloy / lightweight flywheel.????

If so what are you coments on them.??

Either for or against.???

Where did you get it from .???

Im in need of a new Fly for my S2 + need some info as the best way to go.????
See
https://rennlist.com/forums/924-931-944-951-968-forum/201172-spec-clutch-kits.html

For my dilema..!!!!!!!!!!!!!!!!!

Yours hoping for some good advice .....

HAMMER502

I PUT A SPEC LIGHTWEIGHT FLYWHEEL AND STAGE ONE CLUTCH IN AN OTHERWISE STOCK 944(86 MODEL).THIS WAS DONE WHILE THE ENGINE WAS BEING REBUILT.WITH THE FRESH ENGINE AND L/W FLYWHEEL THE CAR WAS A BLAST TO DRIVE(UNTIL I DROVE A FREINDS TURBO,THEN I HAD THE BUG AGAIN).IT HAD A SLIGHT JUDDER FOR ABOUT THE FIRST 1800 MILES,THEN IT WAS FINE.I DID DO AN AUTO-X EVENT WITH 1200 MILES ON THE CAR AND IT SEEMED TO GET BETTER AFTERWARDS.I HOPE THIS HELPS.

WesM951

Good question, i'd like to know as well. My clutch is in need of replacing.

ideola

Here's a X-post from 924board.org on the same topic:
http://www.924board.org/viewtopic.php?t=15170

Similar car, but the same principles apply. Depends on what you want to do with the car. The bottom line is this: if it's a street car, you'll sacrifice off-the-line performance due to reduction in torque (caused by lower rotational mass). If it's a race car, reaching high RPMs faster may be an advantage, which makes it worth considering the reduced rotational mass of a lighter flywheel.

Boricua944

so if you wanted more low end torque, can you get a bigger flywheel?

ideola

More rotational mass = more torque.

Not necessarily bigger, but heavier...flywheel or crank.

Boricua944

So what are some options in heavier cranks and flywheels?

Team SSR

"More rotational mass = more torque.

Not necessarily bigger, but heavier...flywheel or crank"

????????????????????????????????

I have to disagree. Heavier rotating weight will not make more torque. More rotating weight has more inertia and may help marginally by keeping momentum up during clutchless gear changes, but it's a loser everywhere else - including braking.

ideola

Weight and mass are synonymous. See http://ourworld.compuserve.com/homep...ard/weight.htm for a complete discussion.

Bottom line is that something that is "bigger" doesn't necessarily have more mass. Increased mass = increased inertia = increased torque

Obviously, it takes more horsepower to get a larger rotational mass moving, but once it's moving, a larger rotational mass creates more torque. Period. Clearly, there is a practical limit to how much rotational mass is going to be suitable based on the HP capacity of the motor in question. Finding the right balance of HP vs Torque is the key, based on how you intend to use the vehicle.

Conversely, as you correctly point out, more mass requires more stopping power due to the increased inertia once the vehicle is moving.

I don't know if there are stroker kits that would include a bigger crank available for these cars or not. In general, I would think that if you want better off the line performance, that you would leave the crank and the flywheel pretty much stock, and do performance tweaks elsewhere, perhaps by stroking the motor so that you can harness the torque faster, something like that.

streckfu's

Torque is a rotational force, not HP. It takes more torque to rotate heavier/massive flywheels.

Hp is a product of TQ applied over time. So how do you 'balance Hp vs TQ?

A stroked motor produces more torque everywhere. You can't 'harness it faster'. It's already there.


So mass is a constant while weight is the effect of gravity on that mass and can vary.

RMills944

More weight means it has more inertia - true.

That inertia will be moving and keep the engine from engine-braking as fast because it's moving faster and needs more effort to slow it down.

Applying the same math, that weight needs to get up to speed. This means that the engine must put forth more effort to get that mass moving.

torque = weight x length.

Apply this equation and you will see how they get more torque with more weight. The problem is in the application of that. This simply means the required torque to get the flywheel moving will be more. In other words, you need more torque (or effort on the engine's part) to move this object. They are simmply applying the equation wrong.

for a real life example - go put a heavier flywheel on your car and dyno it. I gaurantee you just lost power.

I love physics!

streckfu's

I agree!

ideola

No question, there is a tradeoff between HP and Torque. That was my point. A buttload of HP with no low-end torque is useless for getting the car off of the line. Hence, when I said "balance" HP and Torque, I wasn't referring to a scientific process. I was referring to a tradeoff decision. In other words, figure out how much HP you can reasonably produce with a given engine configuration, and based on that, figure out the optimum rotational mass for your crank and flywheel to produce the desired torque.

As I said in my previous post, that answer will different for each application. A drag racer will have a different setup than a autocrosser than a ralley than a street application.

For me, I want my 928 to have more off-the-line grunt. I'm building a hybrid motor for it. Beefier low end (5.0L short block) with the stock flywheel mated to a 4.7L eurospec top end. This will give me great low end torque, and ~350HP. The pistons will be notched to accomodate valve clearance, and I'll be running 11:1 compression. For how I want to use the car (a mean fast street machine) this will produce a good combination of low-end grunt and HP.

StoogeMoe

This shade tree physics cracks me up. A heavier flywheel does not create more torque. The engine is creating the torque by forcing a piston down a cylinder and turning the crank. The flywheel is just there to balance out the strokes of the pistons and to keep it turning when the cylinders aren't firing.

It's like when you pedal a bicycle. You have no torque when the pedals are straight up and down. Did you ever get stuck going up a steep hill because you couldn't keep the pedals moving? It's the same thing that happens on a light flywheel engine. You release the clutch and the engine dies because you caught it in between power strokes. You don't have less torque, you lost rotational momentum between power strokes.

Hope this helps clear things up.

ideola

I never said a heavier flywheel created more torque. The gist of what I'm trying to say is that the crank and the flywheel are the two most signficant components that contribute to rotational mass. There are other elements, of course, but it is the weight of the crank and the flywheel that primarily contribute to the rotational mass of the engine. One more time: the more rotational mass you have, the more torque can be produced ("can be" is in italics because as you point out there are other elements that go into the creation of torque).

Boiling it down to laymen terms (and yes, I consider myself a layman) if you put a lighter flywheel on your car, the car will not produce as much low-end torque. To put it another way, if you want to launch your car off the line, don't put a lightweight flywheel on it. That's all I'm trying to say. I'm no physics professor, so I'm not going to try to argue the scientific points. I was just making a rule-of-thumb statement.