Any reason to lighten the flywheel on a street 3.0? Options

[moparrob]

I have decided to go with a Kennedy Engineering conversion to mount my 3.0 to my 901 trans.

It seems like you have two options:

1) Keep the stock 228mm flywheel (which they call 9 inch) and buy their ring gear part number 9-915. These are $170.

or

2) buy a new one-piece flywheel from them (with proper ring gear machined into flywheel) made of 1045 steel. Price $300.

Either way you will need a pressure plate, clutch disc and throw out bearing. That costs an additional $356 (for their stage 2 package).

The benefit to the one piece, new flywheel is that you can run a stock 215 mm disc and plate (lower cost, available at any parts store). You can still run the larger 228mm parts with the new flywheel also.

With the ring gear option you are required to use their 9 inch clutch which is more expensive than a stock 215 clutch and must be purchased through them.

The advantage to the larger size (228) aside from the obvious size increase is that they offer up to a stage 4 for that plate, capable of over 600 ft. lbs. of torque, if you are so motivated.

They recommend that you re-surface you old flywheel if you are going to run only the ring gear, and I do not know what that procedure costs from a reputable machine shop. I'd venture the overall costs are pretty similar between (a) using the ring gear and machining your old flywheel versus (b) buying the new flywheel and avoiding the machining costs.

Ring gear plus clutch =$526

New flywheel plus clutch = $656

The difference is $130 (less the cost you'll pay for the resurfacing)

The only other benefit I can think of if you use your old flywheel is that you could have it lightened - if that is actually a benefit. But then again, if you buy a new flywheel you could probably sell your stock one for around $100.00

So therein lies the question - is there any benefit to either lightening the stock flywheel or the Kennedy flywheel for a street driven 3.0? Obviously, I'd like to have this done before I go any further and install the drivetrain parts since there would be no additional labor at this time.

Is the tradeoff between a more freely revving engine and the reduced driveability of the lightened flywheel that noticable? Is there some minimal amount one might want to remove before the problem becomes obvious.

Thanks in advance for your input as I'd like to order something from them soon.

[brp986s]

IMO for a street car don't bother with it, especially if you have to pay extra for it. Depending on how light you go, it can cause problems with shifting due to the engine spinning down too fast. Depending on your cams it could interfere with idle. It can also cause rattle from the gear box. If a 3L isn't fast enough for you it won't be due to light vs std flywheel.

[d914]

whats the future use of car?? 3.0 stock is about 180hp.. plenty of grunt for the street...decent tq...if pure street I'd probably leave alone.

[pcar916]

I'd always go with the larger clutch disc/pressure plate combo. Ultimately it'll last longer, especially if you are careful with your clutchwork. I've been running a very light flywheel (6.75 lb) and the earlier push-type pressure plate on first, a 2.7L motor and then again with the 3.6L motor with no problems at all. Your throttle response is much quicker with the light parts, but you have to be smoother with your clutch and throttle to be kind to all of your power-train bits.

I'd never go back to standard parts, but I'm very careful about who drives my car too. The engine will rev much faster with the light parts, and fall back to idle faster as well. It makes it easier to match engine speed when up and down-shifting. And that'll make your synchronizers happier as well.

Good luck!

[moparrob]

Thanks for the responses.

Yes, at this point it will be strictly a street car and no one else will be driving the car.

It is a stock, '79 3.0 (previously with C.I.S, now Weber 40 IDA), stock cams. The cost is not really an issue, especially when compared with everything else to date.

Wow! 6.75 lbs. is light. The Kennedy flywheel, IIRC, is 15 or 18 lbs.

BRP - your point is well taken. The flywheel is not going to be the difference between enjoying the car or not. I suppose if I ever decide to build the motor, or go to DE events, I could always re-visit the issue.

Out of curiousity - anyone know of any links on how the black art of flywheel lightening is actually performed on that flywheel (i.e. from where the material is removed)?

[Eric_Shea]

None that I can think of. With Carbs and a decent exhaust you should be pushing 200+ driveable hp.

[ConeDodger]

None that I can think of. With Carbs and a decent exhaust you should be pushing 200+ driveable hp.

(IMG:style_emoticons/default/agree.gif) Lightening the flywheel will give you quicker throttle response but it also causes other problems. There is always a trade and usually in drive-ability. In this case, keeping the engine running when stopped on hills and such.
Believe me, 200HP is plenty entertaining in a 914. The Bumblebee Racer was all I could handle at full song on an autocross course.

[IronHillRestorations]

Don't do it Rob, there's no good reason for a street car.

[gothspeed]

No