m20 singlemass flywheel machining

[nando]

Cliffs:
Lighter Flywheels allow engine to change RPM faster.
Makes Getrag rattle more apparent.
Lower inertia makes engine easier to stall (only affects inexperienced drivers).
Great for speed shifting, annoying for granny shifting.


For DD cars, if your normal shifting tends to 'beat' the engine into the next gear, you should lighten your flywheel. By 'beat' I mean the flywheel rpm is higher than transmission when clutch is released. If the transmission 'beats' you into the next gear you should not lighten your flywheel.

Race cars: You will almost always 'beat' the transmission to the next shift, thus lightened flywheels are a good idea. Also, r3v matching will be easier and less likely to break the rear end loose when de-clutching under high lateral load with a poor r3v match.

Huh?? What race car driver is downshifting without rev matching first? if they aren't, their transmissions aren't going to last very long. Not to mention a whole host of other problems you cause by not rev matching (like uh, unsettling the car's balance right before a turn, locking the rear wheels, etc).

You shouldn't EVER force the trans and engine to match RPM by just letting out the clutch. Just look at some of the recent threads where guys have destroyed their pressure plates by doing just that.

I rev match every gear every time I downshift. It's not just a "I can heel-toe" snobbery thing, it's highly satisfying to do correctly, and far smoother than forcing it into gear and letting out the clutch.

I can also downshift way faster than I can upshift (my tranny has high miles and balky synchros, so I tend not to upshift quickly). Having a lighter flywheel helps that happen.

as far as it "stalling easier" and other such nonsense - whatever. we're talking about shaving 5-10lbs off the stock one, not using a 6lb aluminum race flywheel. There's no real drawback to a ~13lb stock flywheel. my transmission has almost 300,000 miles, and the rattle is hardly noticeable.

[clavinZERO]

12.5 lb left on stock shaved flywheel is what I have. No problems. Fun. Little harder to drive. Wouldn't go back. 245,000+ miles on transmission and sound (rattle) did not change versus the stock weight flywheel.

[Kershaw]

ok... to the guy that posted a link "demonstrating a dyno" posting the same numbers....

WELL NO SHIT. a lightweight flywheel doesnt add any horsepower.

but like nando said, any rotational mass you remove WILL make you accelerate faster. lets say you buy a lightweight flywheel and do 9lb enkei rpf1s. only an idiot will not notice the difference in acceleration. braking. turning. and road feel. the suspension doesnt have to work as hard to rebound the reduced weight.

tell, does it take more energy to roll 100lb ball or a 10lb ball? also tell me, did your muscle mass increase any between the two? hmmm... things to think about.

my rx8 has a 8.98lb flywheel. and it feels fucking awesome.

[ZekeTheSneak]

you guys fight alot. I'm doing this for the r3v matching and fun. Now who has had there harmonic balancer lightened? Heard that does wonders as well. BTW i have a clutch stop so I can handle the tricky starts.

[TwoJ's]

I didn't read through all of the banter in this thread. But I didn't notice if anyone mentioned the reason that flywheels weigh as much as they do on street cars... They store kinetic energy, and make the engine feel smoother to an extent. The smoothness is more noticeable on an engine with less cylinders. Also, it is a good thing to have that rotational mass when you are engaging the clutch. You won't need to rev the engine as high to engage without stalling.

Like it's been said, for a street car there is no reason (aside from the "fun factor" that's been mentioned) to lighten a flywheel. But whatever floats your boat I guess. I sure wouldn't get all worked up about it like Luke if someone decides to do it to theirs.

EDIT: I see that we are (I am) beating a dead horse here. Disregard and carry on.

[KennyT]

Huh?? What race car driver is downshifting without rev matching first? if they aren't, their transmissions aren't going to last very long. Not to mention a whole host of other problems you cause by not rev matching (like uh, unsettling the car's balance right before a turn, locking the rear wheels, etc).

The text you bolded should have read engine not transmission. My previous post is edited to fix that.

To explain things in even simpler terms, with an unshaved or dual-mass flywheel in a racing enviroment every shift can be performed in less time than it takes for the engine to spin up/down (matching the new transmission input shaft rpm). Thus the flywheel should be lightened to allow the engine to change rpm as fast as necessary to match shift speed.

If D Stock allowed lightened flywheels mine definitely would be. The several cars I've driven with a light weight flywheel were great fun.

[Aptyp]

also to note, with 13lb flywheel you can still granny shift. It actually made it even easier to relax and drive. Considering in my last E I shifted around 2000rpm and barely ever broke that daily driving, it made car feel much, much better.

So 13lb flywheel is plenty streetable and smooth. Don't know about anything lighter, though.

[ZekeTheSneak]

Thank you all, now should I get the harmonic balancer reduced as well?

[kendogg]

Thank you all, now should I get the harmonic balancer reduced as well?

I've refrained from saying anything, but I have to. That is by far the dumbest thing I've ever heard of anybody doing. The harmonic balancer has a purpose. Do some reading from people who've replaced their harmonic balancer with lightweight crank pulleys and ask them how long it took for oil pump or bearing problems. It's a stupid idea, I don't care if some of the ricer boys in here have done it. Even pro racing teams run true harmonic balancers, most of the elastometers similar to a stock BMW one. And no, they aren't lightweight. Look at how big the S54 one is. Know why it needs to be bigger? Take a wild guess. And it has nothing to do with revving, because that engine freerev's quite quickly.

[ZekeTheSneak]

Just saw products online about the hb so just wondering, same place that had reviews on lightweight flywheels. They sell both light flywheels and different hb's

[kendogg]

Just saw products online about the hb so just wondering, same place that had reviews on lightweight flywheels. They sell both light flywheels and different hb's

Right, because companies that sell parts are always 100% truthful about what said products do to your engine..... On that premise, why are we not all buying Tornado's for their increased fuel economy???

[avery0829]

Getting a quote today on my flywheel -ZeketheSneak

[quickervicar]

I lightened mine, but was conservative with it. Plus, my Spec PP & disc weighed in @ .8# more than the Sachs stuff did. IIRC, I am around 3# lighter as a total system. I love it. Perfectly streetable and fantastic on downshifts.

[ZekeTheSneak]

Ryker machine in Tacoma is machining it for 60 bucks not bad

[ZekeTheSneak]

So a fallow up, Flywheel machined for $60.00, then today i pick it up after being balanced it was 13 grams off. Another $60.00. I will have a picture up tonight or tomorrow but i am impressed with the work.