LWFW to avoid RMS damage - 986 Forum - The Community for Porsche Boxster & Cayman Owners

jaykay · 09-20-2009, 08:36 AM

Just curious as to whether anybody knows whether a light fly wheel could mitigate crankshaft and RMS damage by reducing the overhung weight at the back of the crankshaft. I would think the DMFW at 40 lbs, slightly unbalanced, on a slightly untrue crank could cause undue crank shaft deflection resulting in RMS damage and leaks. I would think by the time you have an RMS leak you already have engine damage.

I was thinking of a LWFW just to prevent this scenario but I am just learning about all the negatives associated with it. I have a very low mileage engine (m96) that I would like to make reliable.

What flywheel would I use to be safe? Do I need a clutch to go along with it? It is not a race car so I would like to keep it as streetable as possible. What are the risks? Will a dynamic balance problem be caused?

Thanks,

jaykay

jhandy · 09-20-2009, 07:31 PM

You will have a balance problem that may cause harmonic resonance failure of the crank. You will have chatter unless you by an certain clutch ( sprung or unsprung) I dont remember. You will have trouble resurfaceing the after market wheel, if they dont make your inserts anymore. Look up flywheel and jake raby in the search. Do the underdrive pulley- 200$ and 10 HP. less rotating mass.

violametallic-S- · 09-20-2009, 09:19 PM

If you have a sprung clutch with a LWFL combo, then the sprung clutch takes in all the vibrations. Thats what ive been reading lately.

Side note, where would one get a underpully you speak of? 10hp gain?

jaykay · 09-20-2009, 09:29 PM

I am running an underdrive pulley now......the one I have is from Mantis racing in Canada. I am sure there are others. I am told it gives +7hp.

violametallic-S- · 09-20-2009, 10:06 PM

Quote:

Originally Posted by jaykay

I am running an underdrive pulley now......the one I have is from Mantis racing in Canada. I am sure there are others. I am told it gives +7hp.

Did you notice a difference?

jaykay · 09-21-2009, 05:59 PM

I desnorkled and put the pulley in at the same time.....so I did feel like the engine had been opened up a bit and was more responsive. The awesome sound from the intake while on the throttle helped psychologically aswell. I am going to look to coming up with an intake tract with no resonance chambers in the search for more sound..

I have seen a dyno showing +5 for the snorkle so that + 7 from the pulley theoretically gives +12!

Your accessories turn slower of course (If I recall correctly...20%). Parking and at full lock my power steering pump will wine. Buzzing around in the power band of the engine at the track all day can damage the power steering pump so slowing it down is a benefit.