Pre-69 2.0l flywheel weight?

[Hebster52]

I've tried to search but came up with nothing..

I would like to know the stock weight of the pre-69 911T flywheel?

[Hebster52]

Still would like to know what the stock solid early flywheels weighs without the clutch and pressureplate?

[Bullet Bob]

Here is more than you ever wanted to know about that flywheel :-)

VOLUME = 4.7599651e+01 INCH^3
SURFACE AREA = 2.1245074e+02 INCH^2
DENSITY = 7.0200000e-04 POUND / INCH^3
MASS = 3.3414955e-02 POUND

CENTER OF GRAVITY with respect to _FLYWHEEL coordinate frame:
X Y Z 0.0000000e+00 0.0000000e+00 0.0000000e+00 INCH

INERTIA with respect to _FLYWHEEL coordinate frame: (POUND * INCH^2)

INERTIA TENSOR:
Ixx Ixy Ixz 2.8434208e-01 -6.5270334e-08 0.0000000e+00
Iyx Iyy Iyz -6.5270334e-08 2.8434213e-01 0.0000000e+00
Izx Izy Izz 0.0000000e+00 0.0000000e+00 5.6729192e-01

INERTIA at CENTER OF GRAVITY with respect to _FLYWHEEL coordinate frame: (POUND * INCH^2)

INERTIA TENSOR:
Ixx Ixy Ixz 2.8434208e-01 -6.5270334e-08 0.0000000e+00
Iyx Iyy Iyz -6.5270334e-08 2.8434213e-01 0.0000000e+00
Izx Izy Izz 0.0000000e+00 0.0000000e+00 5.6729192e-01

PRINCIPAL MOMENTS OF INERTIA: (POUND * INCH^2)
I1 I2 I3 2.8434204e-01 2.8434217e-01 5.6729192e-01

ROTATION MATRIX from _FLYWHEEL orientation to PRINCIPAL AXES:
1.00000 0.00000 0.00000
0.00000 1.00000 0.00000
0.00000 0.00000 1.00000

ROTATION ANGLES from _FLYWHEEL orientation to PRINCIPAL AXES (degrees):
angles about x y z 0.000 0.000 0.000

RADII OF GYRATION with respect to PRINCIPAL AXES:
R1 R2 R3 2.9170918e+00 2.9170925e+00 4.1203381e+00 INCH

The weight is the mass x 386.4, or 12.9 lb

[Bullet Bob]

This is the correct flywheel, right? I have one here I can weigh and I will post the actual weight when I find it.

Bob

[Bullet Bob]

Actual weight is 11.8 lb so the CAD model isn't too far off.

[eapcpa]

Bob,

Relax and have a beer. You are definitely overthinking this question.

[Hebster52]

LOL!
Thanks Bob!

The weight of the custom flywheel I have now is appr. 6 kg. So it is slightly heavier. Wonder if the pressureplate is the same weight for both the 911 and the beetle flywheel?

[Bullet Bob]

Originally Posted by eapcpa

Bob,

Relax and have a beer. You are definitely overthinking this question.

Yeah, I know. I had modelled this some time ago because I wanted to determine the benefits of reducing the weight (percieved power gain in low gears, etc...). I also have a CAD model of the Swiss cheese version. It is nice to actually get to help someone for a change as usually I am the one asking all the questions :-)

Bob

[kenikh]

Very cool; what lightend models did you create and what were your conclusions.

[Bullet Bob]

I was able to reduce the rotational inertia by 16% and if I remember correctly I figured it would be equivalent to ~2.5 ft*lb of torque in first gear. This is dependant on how quickly the engine is revving so in the other gears the difference isn't very significant. It would rev much faster during gear changes and blipping the throttle though.

What I figured is that it requires 34 ft*lb of torque to accelerate the flywheel to 7000 rpm in 1 second. If its inertia is reduced by 16% it only takes 29 ft*lb. If you rev to 7000 rpm and first gear lasts 2 seconds that frees 2.5 lb*ft of torque that would have been acting on the flywheel. The engine would rev considerably faster however.

Of course, there is the chance that I totally butchered this so any other engineers out there feel free to chime in.

Bob

[racing97]

(PRINCIPAL MOMENTS OF INERTIA: (POUND * INCH^2)
I1 I2 I3 2.8434204e-01 2.8434217e-01 5.6729192e-01)

Bullet Bob, was this measurement taken F X T on a photgate timer.

regards

[Bullet Bob]

Originally Posted by racing97

(PRINCIPAL MOMENTS OF INERTIA: (POUND * INCH^2)
I1 I2 I3 2.8434204e-01 2.8434217e-01 5.6729192e-01)

Bullet Bob, was this measurement taken F X T on a photgate timer.

regards

No, these were calculated based on the CAD model geometry. All of the information listed above was simply cut and pasted from an analysis that was run on the CAD model. The analysis took about 2 seconds so it really wans't much work to provide the info. I would guess the CAD modeling took an hour or so but well worth the time to get the mass and inertial properties.

Bob

[Hebster52]

Thanks so far. I've now weighed it on our Laboratory scale and it weight 13.95lbs.

What I wonder is. Should I machine off some more? There aren't much more to take off it...

As the custom made flywheel I have is made from a VW beetle flywheel and uses the VW pressureplate I was wondering whether there might be some differeneces in the weight of the pressurplates too? (beetle vs. 901 pressureplates?)

Just so I could determine the total weight for each assembly.

[racing97]

I have the facility to check rotational mass MOI and there is a chap in Fullerton Ca. that sells an Aluminum 6 bolt Porsche Flywheel. We found that the early steel unit, at least the one we had weighed approx 12.6lbs and his unit was a 6.4 lbs

the input was 200 grams
radius of pulley 12.7mm
angular acccel @ 400 degrees/s/s
gravity 9.8
r*m*g* .0249174

Gave us the following results 0.0349 kg M(2)
119.29 lb-in(2)
This we found was commensurate with Flywheel manufactures such as Tilton Eng.
We do this test on a mechanical apparatus that took quite some time and a little money, but it is quite useful. We have even used it to evaluate rocker arms.
Oh buy the way the original Flywheel with the Copper friction surface @12.6 lbs has a MOI of 254.08 lb-in(2)
Thanks for the fun thread
regards

[Bullet Bob]

racing97,

looks like the results (from CAD) are in the ballpark. English units always throw me off with the whole force and mass thing so I used lbm which is why the values are so small. Multiplying by 386.4 (in/s^2) brings the value to 219 or so.

Is the machine you used designed specifically for this or did you design and construct it? Do you have any pictures of it? I am curious because it sounds like a pretty handy piece of equipment.

Bob

[racing97]

Sorry for the delay our unit is a Photo Gate timer assembly with Math Lab configurable software. We pieced it together and modified the components until it was able perform with a relatively high degree of consistency.
I don't think you can buy a unit to do MOI at least at the time we could not find anything, although you can find this unit illustrated in texts, I believe that is how we came to make ours.
I know Auto Cad used to include the MOI feature I forgot how far F.E.D. has gone in the last few years. Anyways great job on your end hope your project turns out well. P.S. sorry for the picture quality