Light weight Flywheel

[1e13902]

Light weight flywheel with a 5 speed gear box.
I'm green with envy over ClassicJaguar.com's products.
My only concern is how will replaceing the heavy Iron flywheel on my 4.2 with the light weight one will effect rev and torque. I run a 3.07 dif .
Was there a need for the heavy flywheel? counter weight effect? Heavy things in motion tend to stay in motion. but getting it in motion requires alot of energy. Can't see how having a 100LB+ flywheel benifits any engine.
My rear end is for top end speed at the sacrifice of off the line quickness. My 67 ots can give you whiplash running through the gearswithout a head rest, Fast! with 140+ mph with out pushing to redline.
Would all this be an expensive upgrade with little benifit?

Tom

[Heuer]

Tom

My car has a flywheel lightened front and back, competition pressure plate, 5 speed and 2.88 diff. It remains very drivable and tractable. Lightening the flywheel will make the car more responsive to the accelerator (less mass to speed up and slow down) at the expense of smoothness. I initially had it with the standard 4 speed Jaguar box and I could frequently beat the synchro on up changes. The modern 5 speed suits the lightened flywheel better allowing me to make the most of faster changes and more rapid engine acceleration. You have to be circumspect with throttle control to maintain smoothness, blipping the throttle is not good enough - you have to 'set' the accelerator pedal to match road speed. Sometimes, when my mind wanders in slow traffic, and I accelerate in 1st without thinking the car will kangaroo until I get to grips with control. You soon learn to concentrate!

If your engine is out then fitting a lightened flywheel may suit your driving style but certainly not worth pulling the transmission just to add it.

A lightened flywheel lays bare your driving and many people would not like it.

David

[1e13902]

Thanks EDavid, You painted a wonderful picture for me.
Smoothness in the shift is the sacrifice. For a weekend tooling around OTS that might be too much of a performance upgrade.
Yes the engine is comming out for a total rebuilt and time to make the decisions. Wish I had one to test drive.
You definitly tweeked my imagination.
Tom

[Heuer]

Tom

I had a look at the Classic Jaguar alloy flywheel and it is way too light for normal road driving. Mine is a standard Jaguar flywheel that has been lightened by removing metal which makes it far less extreme.

Definitely worth speaking with a specialist company who can tailor the flywheel to what you want from it. Trick is to reduce the mass (allowing faster acceleration) but retain some of the 'flywheel' effect for smoothness. This is achieved by deciding where to remove the material. Taking it out of the centre will make it lighter but retain the flywheel motion. Get the balance right and you will have the best of both worlds!

David

[Moeregaard]

David, your point is well made. I've been considering a CJ alloy flywheel, but wanted to get the thoughts of others before I plunk down $400-plus for something I may not like. I'll be changing my final-drive ratio to 3.07, but will retain the stock Jaguar 'box.

Would you happen to know what the actual weight of your lightened flywheel would be?

[andyp]

Moe

It's not so much the $400, it's having to pull the enginbe again if you don't like what you've fitted.

David will obviously tell you what he has but I have tried both a 12lbs and 20lbs flywheel in addition to standard on the 4.2 motor.

On a track I'd take 12 pounder, on a fast road car I'd go for the 20 pounder.

And what did I fit to my car in the end?

That great big lump of metal from Jaguar.

Andy

[mouton]

Well, my experience is a little different.

I have a CJ lightweight flywheel, installed pretty much as a fluke and by the very generous assistance of CJ as they were rebuilding my engine at the time and gave me an incredible deal -- and did not have my original flywheel in Texas. I threw a rod big time on Sears Point Raceway so the old block and crank were throwaways!

The biggest advantage of the alloy flywheel was the ease of stamping degrees on it well BTDC and ATDC. In practice I was unable to detect any difference in idle, pickup, or overall performance.

As is often the case, however, this was a new engine and so differences would have been due to much other then the flywheel, you'd expect. But the old engine was extremely robust too -- just a perfect stock XK engine.

The other item is that this is a 3.8 and so the original steel flywheel was only a few pounds heavier than the alloy version. 4.2 may need a little more flywheel. But my opinion is that it makes very little difference either on the street or on track.

Jerry