m20 singlemass flywheel machining

[Dyno4mance]

You do realize it doesn't effect the acceleration of the car at all, right? Under load, the engine isn't going to accelerate any faster or slower.

You do realize you are wrong, right?.....a car with a lighter flywheel will accelerate quicker as the rotational mass of the engine is lighter alowing the rotational mass to accelerate quicker and in turn alow the drivetrain and then the car to accelerate quicker...
A heavy flywheel will alow smoother take off...
and to address OP I removed 7 lb from the original SM flywheel with no issues and also removed a further 5lb from the reciprocating mass and the valvetrain, the thing now revs ike a sport bike

[kendogg]

You do realize you are wrong, right?.....a car with a lighter flywheel will accelerate quicker as the rotational mass of the engine is lighter alowing the rotational mass to accelerate quicker and in turn alow the drivetrain and then the car to accelerate quicker...
A heavy flywheel will alow smoother take off...
and to address OP I removed 7 lb from the original SM flywheel with no issues and also removed a further 5lb from the reciprocating mass and the valvetrain, the thing now revs ike a sport bike

I probably would if infact I were wrong.

http://forums.bimmerforums.com/forum/showthread.php?t=1150599&highlight=flywheel&page=3

Here's 2 posts I like to quote from this thread (which are correct):

a ltw flywheel won't get you a half second on a road course. I'd be shocked if you could show it improved a normal person's lap times by a hundredth of a second.

My comparison was phrased the way it was for a reason.

The LTW flywheel, assuming the cars dyno the same, and have the same mass, will accelerate exactly the same. F=M*A Same HP (same F), same weight (same M)... always going to get the same A.

If we look at the tire bit, we are talking about taking how much weight off the flywheel? around 10 lb?
lets say 10 lb evenly distributed about a disc of diameter 254mm (that makes it 10 inches... makes the math a bit easier)
inertia of said disc is 1/2 * M * r^2
so we have 0.5 * 10 * 5^2 = 125 lb-in sec squared

now we look at the difference in two tires:
a 235/40-17 ranges in weight from 20 to 25 lb.
lets take only 4 lb of that and say its all near the outer surface.
a 235/40-17 has a diameter of about 24.4 inches. we'll put that difference in mass at about 24 inches.

inertia of a hollow cylinder (hoop) will be M * r^2
so 4 * 12^2 = 576 lb-in sec squared per tire (you've probably got about 4 of these on your car.... )

see where I'm headed with this?

Stock flywheel is around 25 lb iirc. (i'll throw one on a scale tomorrow if i remember.) OBD-II M3 flywheels are under 23 lb. so a 20+ lb difference will be difficult with another flywheel while still using a conventional clutch arrangement.

as for the numbers, if we assume that the mass saved by the ltw fly is doubled, then the inertia there is doubled... but still half of the difference in inertia of one tire.

If we keep our 4 lb difference on the tire as the baseline, and we keep leaving gearing out of the system, to match the inertia change itself, we need to make the flywheel:
(4 * 576) / 0.5 / 25 = 184.32

184 lb lighter.

I don't see us easily finding a way to make the flywheel 184 lb lighter than it is now...

if we correct for gearing:
1:1 5th gear and a 3.15:1 final drive.
we'd only need a 58.5 lb lighter flywheel to equal the change in tire inertia.
3rd is a 1.66:1
so that gets us to only needing a 35.25 lb lighter flywheel than stock to equal that change in inertia from the different tires.

as for an equation that proves that it helps, whats the mathematical symbol for wallet? ;)

Keep in mind, this is in reference to an E36 (~25 lbs flywheel stock), so the numbers are slightly off, but being they're starting with a heavier flywheel, it even proves my point further.

[StereoInstaller1]

LTW flywheel is ricer crap no matter what you guys say. The intertia of your car means the .00001% of weight you shave basically does dick...but think what you want, I will still think you are a clown with a car that rattles while you tell yourself that you are a racer.

BTW: Cars built for racing (ya know, ones that take a trailer to the track) are a whole different ballgame. I only laugh at the clowns rattling at a stoplight.

[Chaos Theory]

You don't make peak power at low rpms so wouldn't getting to your power band quicker be considered a benefit?

[StereoInstaller1]

You don't make peak power at low rpms so wouldn't getting to your power band quicker be considered a benefit?

well of course it would IF you were actually making a difference...but shaving a couple pounds off that spinning mass also means you are likely to have to slip your clutch more, so launching sucks. As soon as you are moving you have all the spinning mass of your tires/wheels/brakes,then all the whirly bits in the drive axles/differential/driveshaft/transmission...well, if you think shaving 10 pounds off the clutch is gonna help do anything except make zoomie noises while you are sitting at a light (fully negated by the goddamn rattles IMO) well, that just makes you a ricer.

None of the above rant applies to real race cars BTW. Ones that take a trailer to the track, ones that have no chance of getting anywhere on the street for fear of IMMEDIATE Police attention, y'know, RACE cars...they need lightened flywheels. If your car has a license plate it is NOT a race car, period.

[Jand3rson]

Hmm quicker revs vs the engine having to labor to move the flywheel is reason enough to swap em for me. When I swapped out the one on my M50 back in the day it was like night and day. The slight rattle oh wheel it's an old car.

I'm going to do a lightened one on my M50. The only thing you want to be careful of is going too light (removing too much material). The last thing you want is a flywheel grenading on you.

Luke, did you run out of Vagisil a little early this month?

[gearheadE30]

my lightened single mass doesn't rattle.... it's at 15 lbs right now.

[ZekeTheSneak]

I was thinking shaving it down to 13 pounds, from what I've heard everything works out ok. Are people cutting them down themselves? Or having a machine shop do the work. I have plenty of friends with lathes and the mechanical skills

[Jand3rson]

I was thinking shaving it down to 13 pounds, from what I've heard everything works out ok. Are people cutting them down themselves? Or having a machine shop do the work. I have plenty of friends with lathes and the mechanical skills

You need to have it done by a machine shop, or someone who can do it exactly right. If it's not done perfectly and balanced properly, it will spin out of balance and cause serious damage.

[ZekeTheSneak]

Thanks, yah I'm going to call around after the holidays. Thank you all, didn't think it would start such a bitchfit about rattles but this is r3v, happy holidays!

[F34R]

You need to have it done by a machine shop, or someone who can do it exactly right. If it's not done perfectly and balanced properly, it will spin out of balance and cause serious damage.

1+
Think of it JUST like a tire, if it is not balanced it will wobble.

I just got mine done from my Uncles machine shop. Cost 64 dollars and weights almost the same as JB, UUC flywheels. Went with 13lbs.

Here is a picture of it:


By e30f34r at 2010-11-25


By e30f34r at 2010-11-25

[AndrewBird]

Where exactly is the rattle you guys speak of coming from? I've never heard of a lightened flywheel rattling. I don't see how a solid piece of steel can rattle, so it must be something else, right?

[F34R]

Where exactly is the rattle you guys speak of coming from? I've never heard of a lightened flywheel rattling. I don't see how a solid piece of steel can rattle, so it must be something else, right?

It is from being too light, or done wrong. Also you got to think about all of the given things in play: pressure plate, torque from engine. Everything could make an issue if done wrong.

Could snap and shatter if too much is removed. I have heard of 11lbs being run with a 6 puck, no issues. But I WOULD not do it, I felt happy with 13lbs.

[Sean]

It is from being too light, or done wrong. Also you got to think about all of the given things in play: pressure plate, torque from engine. Everything could make an issue if done wrong.

Could snap and shatter if too much is removed. I have heard of 11lbs being run with a 6 puck, no issues. But I WOULD not do it, I felt happy with 13lbs.

Mine rattles and it was a Metric Mechanic one...

My understanding is it's from the transmission? Mine only rattles when I have the clutch in (as in, the tranny is turning in neutral)

[Dyno4mance]

I probably would if infact I were wrong.

http://forums.bimmerforums.com/forum/showthread.php?t=1150599&highlight=flywheel&page=3

Here's 2 posts I like to quote from this thread (which are correct):









Keep in mind, this is in reference to an E36 (~25 lbs flywheel stock), so the numbers are slightly off, but being they're starting with a heavier flywheel, it even proves my point further.

Idiot....I guess because "techno 550" (or should I say "notech 550") said it over on bimmerforums it must be correct