Light weight flywheel - good idea?

[Cobra 29]

I have a FMS 351W crate motor that is rated at approximately 425hp. The doc says it has a steel billet flywheel. My ERA Cobra has 3:31 rear gears and a Tremec 5 speed. When I switch to the Tremec TKO600 RR (2.87 first and .82 fifth gear), I want to consider changing to a lighter weight flywheel for quicker engine revs but do not want to lose much "street manners" especially pulling away from a stop.

Anyone know what the weight is on an FMS steel billet flywheel? The engine was assembled in 1995 / 1996. Some performance flywheels are steel or alumimum, some weigh as little as 15 lbs. Are these light weight flywheels a good selection for spirited street driving? I would like to see quicker revs.

[LMH]

Driving my brothers FFR with a light aluminum flywheel isn't bad at all, and it's a 302. These vehicles are so light that I personally don't think it makes it hard to drive. Especially with your 351w, I don't think you'd have a problem.

My 68 Camaro was another story!
Larry

[Tim Brewer]

Aluminum flywheels will quicken your revs, but I wouldn't say you will notice a BIG difference between the two. I doubt your car will lose any street manners. Go for it, I did..
Tim

[DavidNJ]

The issue is moment of inertia, of which weight is a component. The low inertia setups also have a small radius, 4.5, 5.5, or 7.25 vs 11"

[Cobra 29]

DavidNJ, I am not sure I understand your reply. I am planning on installing a standard diameter clutch and flywheel but as I understand the replacement flywheel could be 15 lbs in weight versus the 40? lbs of stock or steel billet (one that I am using now) flywheel.

[speed220mph]

Cobra 29
The rule on flywheel weight is as you go bigger with the engine, lighter with the car and higher on the gear ratio, you can go lighter with the flywheel. All of these factors say to go with a lighter flywheel. It's all about inertia.

[scottj]

Cobra 29,

As you have said, the aluminum flywheel, though lighter, still retains the stock diameter so the effect will not be that noticable. Where as the low moment of inertia units, as DavidNJ has said, are much smaller in diameter. These units have very noticable effects due to the much lower polar moment of inertia. I've run an aluminum flywheel on the street and found no drivability issues at all. I now run a 7-1/4" low MOI unit and can't say the same anymore.
Scott

[DavidNJ]

Scott,

Could you elaborate on your setup and experiences?

Thanks,

David

[scottj]

Originally Posted by DavidNJ

Scott,

Could you elaborate on your setup and experiences?

Thanks,

David

David,

I was running a 3.54 gear, a Richmond 5spd, an aluminum flywheel, and an 11" Long clutch behind a 434 cid small block. It has a Super Victor intake and a solid roller with 264*/272* @ .050, 106* LS, .690/.666 Lift.
With that cam it may seem hard to believe that it was very easy to drive on the street, but it was, and initially most of the miles were on the street. The weight of the aluminum flywheel was a non-issue as the car was very easy to get rolling. The problem I had was downshifting the Richmond on the roadcourse. I would not recommend that trans for serious track use. The Richmond was replaced with a Jerico 4spd, a 7-1/4" Quarter Master button clutch, and a reverse mount starter/bellhousing. As you can imagine, on the street the button clutch won't tolerate slipping at all and the Jerico requires very precise upshifts and downshifts when at part throttle. In short, it's a lot of work but it can be done without damaging the equipment.
On the track, the low polar MOI allows lightnening fast downshifts as the revs can be matched very quickly. The clutch and trans swap accounted for 5-6 seconds off my lap times.

Sorry for being long-winded.


Scott

[DavidNJ]

264*/272* @ .050, 106* LS, .690/.666 Lift...now that's a spicy meatball!!! A non-carbon button clutch really can't take any slipping. They heat up quickly. A 7.25 will be much better than a 5.5" or 4.5" though. In any case, they are all unsprung. With the 5.5" clutches in oval racing, the rule of them is they get virtually all their wear in the paddock.

What people have done in the Supra and I believe Evo communities is use carbon clutches. These are really light. However, they can take an incredible amount of slipping. Depending on the manufacturer, when hot some become very grabby. Too grabby for driving in traffic. Others, I believe including Tilton, are still managable.

The typical setup in those environment is to use an OE diameter clutch with a double or triple disc 7.25" carbon clutch. Sometimes the outer part of the flywheel is not solid.



Does the car idle ok with the light setup, or did you need to raise the idle?

Thanks,

David

P.S.
What valve spring and rocker setup do you use?

[scottj]

David,

Idle was left unchanged @ 1200 rpm.

As far as rockers... I don't remember if this motor has a Jesel or a T&D shaft system. Valve springs in all my motors are 9995 Gold Stripe Isky Tool Room springs.

I get the impression that you are involved in circle track racing?


Scott

[Cobra 29]

I was not expecting the advanced course on smaller diameter clutches to reduce weight as well. What makes of regular diameter flywheels (157 tooth) have others had? What about light weight steel (billet?) versus alumimum?

[LMH]

Fidanza aluminum is what we used on my brothers car and it's what I will use on mine. It has a changable disc surface as well as changable counter-balance weights or zero balance depending what your engine requires.
Larry

[DavidNJ]

Was talking to Gordon Levy today about Mustang suspensions (someplace to put my motor before a Cobra is available) and I asked if he knew about a clutch I could use.

Well, apparently he had worked out a setup with Quartermaster. In is not listed clearly in the Quartermaster catalog; and not at all on their web site. It is 18# and with lower inertia because of the smaller diameter. Not as low as a 7.25" or 5.5", but much less than an 11". Cost is managable, under $1000 with aluminum flywheel. The disc is sprung, which makes engagements easier. Torque is either 500# with an organic lining, 600lbf-ft with a metallic. Unfortunately, that is two small for a strong 392, 410, 427, or 434. But should be great for a 289, 302, 331, 347, 351, and less than extreme 392 or 410.



Anyway, I very happy because I found my clutch!!!

[914fan]

As far as lightened flywheels you should not have any problem. Lets look at it this way. Some small 4 cylinder engines have flywheels lightened to 10 or 12 pounds. The flywheel weight affects cruising more than anything. Your rpm's will build faster with a lighter flywheel, however if everything else is still heavy then you have to ask what the point is. With a heavier flywheel you can cruise using less fuel. the heavier fly has more Inertia. It is important to consider all aspects of rotating weight. A good balancing job includes the flywheel, pressure plate, and associated bolts. If youe engine was balanced to a good degree a lightened fly can throw off your balance job. The weight of everything else (pistons, rods, crank) will compensate for a lighter flywheel, and you should see no problem. As I said I have seen many stret 4 cylinder cars running 10-12# flys.
A LMOI fly sounds like bs. I could be wrong, but if you remove weight from the outer edges of the fly it that not the same in effect as running a smaller fly. Say a 10 in disk lightened mostly on the outside is equivelant to a 9 in disk or therabouts. And you retain the abiliy to run a larger (more surface area) clutch. Again I could be wrong.

[mylesdw]

Originally Posted by 914fan

The flywheel weight affects cruising more than anything.
<snip>
With a heavier flywheel you can cruise using less fuel.

I disagree; at a steady speed the weight of the flywheel is virtually irrelevant and will have an insignificant effect on fuel consumption.

Removing weight from the flywheel is exactly the same as removing weight from any part of the car except that gearing comes into account so that removing 1 lb from the flywheel is equivalent to removing around 15 lbs from the body weight (in first gear). The effect is the same; it allows the car to accelerate faster for a given force applied.

[DAVID GAGNARD]

I've been driving a 3200 lb 65 Mustang since 1995, it has a 35 lb. steel flywheel and a 350hp 351-W...........test drove my road race car this past week, 331 cu in, 472 hp, 15 lb aluminum flywheel and light weight where ever I could in the driveline, have not wieghed the car yet, but it should come in around 2600lb or a little less, at 3000 rpms in forth gear I steady gave it the gas till it was 80% full throttle and in a few seconds I let off cause I thought the clutch was slipping, that's how fast the rpms came up, did it again a few times with the same result, but then I have never driven anything like this before and was used to a lot less hp and heavier rotating mass..........that thing winds up realllllllllllll fast and no doubt the alum. flywheel along with a few other light weight components made the difference...............

David

[DavidNJ]

The flywheel comes balanced to the rotating assembly: 0, 28 oz-in, 50 oz-in. Anything really high reving should be internally balanced if possible. Although that is difficult with a short stroke crank and heavy rotating pieces.

The problem with the lightweight stuff comes when moving from rest and light throttle, low engine speed stuff. The inertia keeps it from stalling. With low inertia, you need more finesse on the throttle and clutch.

[mylesdw]

Originally Posted by DavidNJ

The problem with the lightweight stuff comes when moving from rest and light throttle, low engine speed stuff. The inertia keeps it from stalling. With low inertia, you need more finesse on the throttle and clutch.

A 'quick' calculation shows that lightening the flywheel should have little effect on moving from rest. If you went from a 40lb to a 20lb flywheel you would need to raise your rpm by just 100rpm when moving from rest to have exactly the same energy stored in the rotating assembly. I doubt whether one would notice the difference.

[quickjack]

So, instead of 7,000 rpm you need 7,100 to move from rest?