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From digest.v6.n912 Wed Jul 23 07:26:31 1997
From: "Carl Buckland" <>
Date: Tue, 22 Jul 1997 23:55:44 +0000
Subject: Measuring Lt. Flywheel Effects

Neil Maller answers: From: "MALLER.NEIL"<>
Date: Mon, 21 Jul 97 18:07:38 -0500
Subject: Re: <E36> Lightened Flywheel Q

>From: scott bennett <>
>Date: Sun, 20 Jul 1997 23:08:49 -0400
>Subject: <E36> Lightened Flywheel Q

>Well I've been hearing great things about the lightened
>flywheel and thought I would pose a couple questions I had.

>My understanding is the stock M3 flywheel is 28Lbs. The
lightened one is 10 Lbs. This is about 1/3 the weight and

>I do not doubt that the revs feel quicker i.e. the
>transmission spins up and drops off faster. This will
>certainly make a car feel faster and more responsive. What
>I doubt is that this 20 Lb mass reduction yields significant
>rear wheel HP gains. Has anyone put a car on a chasis dyno
>before and after this mod?

Neil says

This was discussed in detail not long ago. Lightening the flywheel cannot result in increased steady state horsepower as measured by a dyno. After all, the flywheel is not an energy creating device. However since a flywheel does absorb and store some of the energy generated by the engine during acceleration, a lighter flywheel does result in increased transient state energy delivered to the rear wheel, and some therefore measurable acceleration improvement.

It would be possible to calculate these gains. However to do so one would have to know the inertia of both the stock and lightened flywheels, not their weights. Flywheel weight alone is not a good measure of the effectiveness of a modified flywheel. Indeed it would theoretically be possible to have a heavier than stock flywheel which nonetheless had lower inertia (although I can't imagine why...).

Neil Maller
96 M3, stock high inertia flywheel


Neil's comments are right on the money, and describe the effect well. No one ever said that a lightened flywheel would increase horsepower, but it sure does DEcrease acceleration times. Herb Adams, in his book CHASSIS ENGINEERING, says that "..the effect of reducing rotational inertia on driveline parts has 15 times the benefit of just reducing the weight of the car." I have been intrigued with this statement for months, and wish that I had followed his suggestion a long time ago and gone to a lightened flywheel. I am not an engineer (obviously), but I do have enough seat time to have a fairly refined butt dyno, and I can tell you that the difference in how the engine spools up is not subtle, but positively sensational. I wish that I had done some quarter mile times (yeah, sure, I go to the drags all the time) before I installed my lightened flywheel, so that I could provide reliable, numerical evidence. I didn't, so believe what you choose, but I can think of absolutely no reason NOT to go to the lightened flywheel. It is the single most important modification that I have made in quite a while, and I have made quite a few.

BTW, I recommended that those interested in getting a high quality lightened flywheel "call Anthony at BMP." This seemed to offend

Rob Hatrak <Hatrak_at_ix.Netcom.Com>

All of this BMP stuff recently is bordering on pimping

I get GREAT deals from Mark _at_ Bekkers. Everyone please call him so that = I too can get drastic discounts in return for the referrals and the = reduction of his advertising costs.

Rob Hatrak
Sin City Chapter
95 M3

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Dear Mr. Hatrak,

.............I have nothing to gain by sharing my personal, imperical exercises other than the joy of sharing and receiving back worthwhile information. . If Mr. Hatrick has something specific to offer, than I invite
him to do so. In my opinion, telling the list that "I got a part from a well known
supplier, but you will have to guess who it was" is worthless blathering. As Mr. Maller points out above, not all lightened flywheels are created equally. The one that BMP supplies is first class, just like most of the other products that they sell. I also do business with Korman, Will Turner, Dinan, and even the Factory, and all of them have supplied, for the most part, products worthy of putting onto/into a BMW. I have on many occations mentioned each of them by name, and supplied phone #'s. If I try out a *specific* product, I will continue to identify who sold me that product, so that others can know of at least one source for that product. We had that whining about "don't have any commercialism on the Net" thread beat to death a year ago. Sorry you are offended, Mr. Hatrick.


Carl Buckland
Salt Lake City, Utah
E36 M3, #27, CSP

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