Lightened Flywheels

[mid life crisis]

i have milled out heaps of flywheels for speedway and get them rebalanced after the machining. in 20 yrs ive never had one exploded or even seen one let go . the closest to that i saw was the rear flange of the crank snapped of a car taking the clutch and flywheel and gearbox with it . if your doing any sort of track work a scattershield is a good investment to stop bits comming into the car u have to have a scattershield in every sedan class in speedway right from street stocks to super sedans . not sure if it's the same fpr circuit cars tho

[skyla]

Funny thing tho, my road car (also RB20DE) eats the rallycar for breakfast under acceleration anywhere in the rev range and it still has the std flywheel.

Rach, before you put they flywheel in do some standing sprints (you still have a timer thingy right?) and some more after. Want to see how the numbers change.

Yeah but thet red GTS of yours is a bit of a freak (I mean in a good way) and has more power than the rally car, so it doesn't really surprise me that the red ones quicker. Shane do you have any problems with driveability and gear changes with the rally car?

Good call hadn't thought of testing things with the G-Tech, will let you know the results when the time comes.

Edited September 20, 2007 by skyla

[GTS4WD]

Depends what you want to do to the car:

Drag:

You want a heavier flywheel to keep momentum (and hence revs up) between gear changes..

Circuit:

Your revs will drop and climb quicker, shortening braking distances and reving out quicker..

Pros of lightened flywheel:

Revs out quicker..

Revs drop quicker..

Cons of a lightened flywheel:

Its harder to get car off the line quickly..

Harder to match up revs in double clutch, heal and toe etc.

Heat is tranfered to clutch, preassure plate etc, because the flywheel is thinnner, so it cannot take as much heat as a stock flywheel so it transfers heat to things it is in contact with..

The price..

Plus the bitch of installing it..

Anywhooo..

thats my rant..

[scathing]

Drag:

You want a heavier flywheel to keep momentum (and hence revs up) between gear changes..

Not being a drag racer, I can't say for sure, but is that actually correct?

A lighter flywheel gives you more in-gearacceleration, which is the ultimate goal in drag racing. If you want to keep your revs up during a gear change, you just keep your foot on the throttle. Its not like your right leg is busy doing anything else.

The revs falling away faster also makes it easier to pick up the next gear, as you're not sitting there waiting for the revs to drop to mate to the next gear. On the way back down, a lighter flywheel makes the engine more responsive to a blip of the throttle on a heel-toe. I found it harder to change gears slowly with my lightened flywheel since the revs fall away too rapidly, but easier to change gears fast.

The only place where its a con is on launches, where the car is a little more finicky, but if you're doing a drag launch you're not as likely to bunny hop or stall the car. It takes a little while to get used to, and I still launch roughly at a set of lights, but if I'm giving it a hit out of pit lane or on a drag strip I don't have any issues getting the car away. Unless you've got so much grip you can do a full-bore clutch dump and not wheelspin, you can always cure your launch slowness with more RPM.

[Eug]

Not being a drag racer, I can't say for sure, but is that actually correct?

it's been proven in drag applications that a heavier flywheel is faster for turbos, as you stay on boost while you change gears. unsure for NA though

[skyla]

So speaking hypotheticaly, it would be a good idea to use a short shifter with a flightened flywheel, as the short shifter reduces the amount of throw and allows for quicker gear changers? I'd imagine this would help in keeping revs from dropping to much between changes and loosing too much speed.

[Cubes]

it's been proven in drag applications that a heavier flywheel is faster for turbos, as you stay on boost while you change gears. unsure for NA though

Proven by who?

Its impossible to stay on boost while you change gears.

I've ran with the std heavy and a lightened and the lightened wins hands down.

The differences I have noticed was the car required a few more rev's to get off the line without bogging down.

Getting out of the hole was easier and wheel spin was easier to control.

Gear changes felt easier and quicker at WOT with big decrease in missed gears; the box had iffy syncro's.

The car felt noticeably more brisk in first and second gear; it felt as if it had more torque and would accelerate quicker. Response improved.

Technically for a typical turbo'd car which rev's high and has a low diff ratio (numerically higher) the motor accelerates/revs faster to provide the same road speed acceleration as a larger n/a v8 for example. The lighter flywheel allows the motor to accelerate faster due to a decrease in inertia; as a result this WILL translate in to improved road speed acceleration. Especially in the lower gears.

A lightened flywheel does next to nothing for the higher 4th gears etc as the motor rev's out considerably slower; as a result the resistance to acceleration or deceleration (inertia) has little effect.

Hope that made sense.

[unarmed_skyline]

cubes thats exactly how i though it all worked but i dont have one so cant comment either way

[Eug]

Proven by who?

Its impossible to stay on boost while you change gears.

I've ran with the std heavy and a lightened and the lightened wins hands down.

The differences I have noticed was the car required a few more rev's to get off the line without bogging down.

Getting out of the hole was easier and wheel spin was easier to control.

Gear changes felt easier and quicker at WOT with big decrease in missed gears; the box had iffy syncro's.

The car felt noticeably more brisk in first and second gear; it felt as if it had more torque and would accelerate quicker. Response improved.

Technically for a typical turbo'd car which rev's high and has a low diff ratio (numerically higher) the motor accelerates/revs faster to provide the same road speed acceleration as a larger n/a v8 for example. The lighter flywheel allows the motor to accelerate faster due to a decrease in inertia; as a result this WILL translate in to improved road speed acceleration. Especially in the lower gears.

A lightened flywheel does next to nothing for the higher 4th gears etc as the motor rev's out considerably slower; as a result the resistance to acceleration or deceleration (inertia) has little effect.

Hope that made sense.

ok i suppose i should have worded it more specifically if you're going to be picky.

well not stay on boost whiles changing gears, but staying in the rev range where you would be making boost - since you're not dropping down in rpm so quickly; and having to build up again

proven by the rigoli's and their old drag subaru. i'm sure there's other variables involved and no doubt it would vary from individual to individual, but they found faster 1/4 times by swapping back to the standard heavier flywheel.

[Cubes]

The inertia of the flywheel has absolutely nothing to do with keeping the car on boost when flicking through the gears.

When you click the next gear, release the clutch and open the throttle back up the road vs engine rpm is fixed.

The only affect it will have is that a heavy flywheel will be harder on syncro's and your driveline. It wil chirp gears easier.

Once you start accelerating the motor has to overcome the flywheels inertia; this is where lightened flywheels have their advantage. Which is why track cars run lightened flywheels; to increase response due to less inertia.

Exactly the same reason why the GTR runs 2 smaller turbo's instead of 1 large turbo. To reduce inertia as a result increase response when rolling out of those corners.

Obviously there is the extreme; if you go too light its not a good thing. Possibly what the suby experienced due to its high grip levels.

Drag subaru. Drag = large amounts of grip. Huge amounts of grip requires a lot of torque to get off the line without bogging down; possibly this is what you meant by falling off boost?

For a street RB; you can't go wrong with a nice 5kg lightened flywheel.

Throw a set of slicks on it with a big turbo and you may find it bogs a tad on the launch. Which hurts 1/4 times.

[scathing]

well not stay on boost whiles changing gears, but staying in the rev range where you would be making boost - since you're not dropping down in rpm so quickly; and having to build up again

But whether your RPM falls at all is a function of your throttle, not your flywheel.

You could have a 1 gram flywheel, that practically bends space/time with how fast it drops once you lift off the throttle, but if you never lift off the throttle (say, go to part throttle when you hit the clutch) you can keep your RPM up in whatever band you want.

That RPM rate of drop only matters for street use. On the track or strip you can drive around that rate with very little cost or difficulty, but reap the rewards of less drivetrain inertia.

[Eug]

i suppose it also comes down to driving style as well (i.e. flat shifting, granny shifting, revmatching, whatever). regardless, i still wish i had put one in when i did my clutch, i'd be around mid pack with the gtsts i reckon

[scathing]

i suppose it also comes down to driving style as well (i.e. flat shifting, granny shifting, revmatching, whatever).

Exactly.

And it doesn't matter if you win by an inch or a mile.....

[screamin']

Yeah but thet red GTS of yours is a bit of a freak (I mean in a good way) and has more power than the rally car, so it doesn't really surprise me that the red ones quicker. Shane do you have any problems with driveability and gear changes with the rally car?

Good call hadn't thought of testing things with the G-Tech, will let you know the results when the time comes.

Only thing I've noticed is the dirty big flat spot around 3000 - 4000rpm. You've seen the dyno plot from the Dyno day a while back aye? Can be a real b1tch coming out of turns, I really struggle to get off them when I've just dived up under someone. Have to actually kick the clutch to get it going, so they don't pass me like i'm standing still!

Yeah I know the red one has more poke, but i would honestly expect a lighter car on semi-slicks, with a lightened flywheel (and flat shifting!) would at least get the jump off the line in the first couple of gears.

[MissR34]

omg im so confused now..........................

so should I get a lightened flywheel????? or would you like more info on how i drive to help me decide LOL

it appears that everyone has there opinion on it, but im a wee bit confused on it all still , my bad

just think ive got gazzanats in about 3 weeks and i dont know how my clutch is gonna take it cause im doing the go to whoa, and cause ive burnt the clutch a couple of times, im just preparing myself for the worst if it comes down that i need to replace the clutch, might as well do the flywheel as well...

the guy at extreme clutch here in adelaide did say that some cars take well to lightened flywheels and others do not (eg BA falcons or whatever they are called), and that my little N/A RB engine should be ok with the lightened flywheel........................thats why i asked

[djr81]

Yes you should get one.

[Cubes]

I think the important thing to remember is once the car is moving the lightened flywheel is a good thing.

Getting the car moving is the more challenging part with a lightened flywheel; especially if it doesn't have enough torque to break traction to start with. Which depends very much so on your setup; diff condition, tyre size and tyre type (semi's etc).

If you have the torque to break traction then I'd recommend a lightened flywheel; if not it may make the car a bit of a pig to drive.

If its 4wd.. Again the same thing; 4wd's can and do break traction when launching quite easily; if you run a big turbo with sticky tyres its easier to bog off the line so you may end up going backwards and not screaming off the line like it used too.

[SKiT_R31]

omg im so confused now..........................

so should I get a lightened flywheel????? or would you like more info on how i drive to help me decide LOL

it appears that everyone has there opinion on it, but im a wee bit confused on it all still , my bad

just think ive got gazzanats in about 3 weeks and i dont know how my clutch is gonna take it cause im doing the go to whoa, and cause ive burnt the clutch a couple of times, im just preparing myself for the worst if it comes down that i need to replace the clutch, might as well do the flywheel as well...

the guy at extreme clutch here in adelaide did say that some cars take well to lightened flywheels and others do not (eg BA falcons or whatever they are called), and that my little N/A RB engine should be ok with the lightened flywheel........................thats why i asked

if your keeping it na especially, i say definitely do it, it makes alot of difference, the whole car heaps snappier and more fun.

theres no power change, but the car accelerates faster and easier, with obviously less direct load on the engine, likewise if you lightened the entire drive train (flywheel, clutch, balancer, accessories, tail shaft, wheels) the car would be alot quicker without the engine actually making any more power, and lets face it, with n/a's unless you want to spend big bickies, there aren't a great deal of mods out there to chose from. You will shave a tad off your 1/4 second time and it will be snappier in the twisties/track, you will need to control the load more with your accelerator as you'll have less built up momentum, taking off changes a bit but isnt harder and you learn it quickly - if you lighten the rest of the drivetrain (wheels/clutch/shaft) it would feel great to take off in.

I noticed no negative change in economy, and even with high end cams never stall with my low and lumpy idle, if you can afford it, its a great mod.

pretty much the reason why people say they're easy to stall, is because apparently they never learnt to drive... for a smooth take off you should pick your revs (say 1000rpm or 1500rpm - depending how quick you take off) hold the revs at that, as you ease the clutch out apply more throttle to keep the revs at that so that when its engaged the car is moving at that rpm, you do this quckly and smoothly watching the tacho and learning the sound of the revs, its how you take off smoothly, with a lightened flywheel, with the less momentum, obviously it takes a few launches until you get a feel of how much the engine slows and how much throttle you need.

one big bonus for me was how quickly the car free rev's, as i do not down shift without rev matching, so blipping the throttle is heaps easier and much more direct (doesn't slowly rev then get quicker as the car makes torque - well not as noticeably, more just jumps to the exact revs) so you can down shift quicker and smoother, with more accuracy.

is harder to snatch second on-the-spot though, if that worries you (haha - burnout)

[Cubes]

Skit 31.

What cams are you running? Duration/Lift?

Got any audio/vids of how it lopes over? Very keen to have a listen.

[NA_R33]

Theres a reason Pro Stock Drag Cars (6 speed manuals) have the lightest drive train components possible ie, carbon tailshafts and what not, i think people get hung up with the fact that a lightened flywheel makes the car easier to stall from a standstill. This is where it ends, less rotating mass = more power/torque whatever you want to call it, therefor the car will go quicker regardless of application in general terms... its as simple as that.