Lightened flywheels

[JiMiH]

Apart from obviously being lighter and therefore requiring less effort to turn them, what kind of difference are you going to notice in the hot seat if you get a lightened flywheel?

Better acceleration?

[lad13s]

you will hit the higher revs quicker becauseit has less time to spin up the lighter weight

thus u can get the power down sooner, i think aceleration is the same, just onset is quicker??

someone will be able to help u out in more detail no doubt.

[Billzilla]

No negatives on mine at all.
I went from a 7kg flywheel to a 3kg alloy one, and the idle didn't change at all, nor was the low-rev torque worse.
It even pulls better in top gear at any revs. ;)

[Matty]

Got mine shaved down, makes a great improvement to throttle blipping (eg heel n toeing).

Bill, just curious to ask - several people have said to me "don't go too light as you will lose low end torque" - but as a mech engineer I can't see how that argument possibly stands up, inertia is inertia and the less the better... (perhaps some unevenness in reciprocating speed affecting the combustion cycle?)

I don't get it and I think it's BS and the opinions of those who have really light FW's seems to back up the fact that there's nothing to lose (except maybe easier to stall).

[Billzilla]

Yeah, I can't figure it either.
But I'm sure that different people with different engines get different results, so who am I to differ?
As for stalling, yeah, mine's a right little darling like that but I'm pretty used to it now.
Got the tyres changed the other day, and the tyre guy wanted to drive the car up onto the lift. I let him, but warned him it's a bitch to drive if you're not used to it. He laughed, and said that he's driven ported rotaries and so on. He only stalled it three times, so I was naturally impressed! :lol

But seriously, I agree that for a performance engine there's relly not a lot of negatives to a light flywheel. I've seen a couple of cars that have them too light though, and they're very hard to get off the line.
For example, we could go lighter with my racing car flywheel, but I really don't want to. ;)

[Hypertune]

Noticeable positives
- Improved acceleration
- Better engine braking
- Improved throttle response
- Can be fitted during routine maintenance

Hidden positives
- Crankshaft resonant frequency is higher
- Less H.P to wheels lost accelerating internal engine mass

Noticeable negatives
- Reduced fuel economy – (Now you believe you are Fangio)
- Your girlfriend hates the way you now drive
- Poor idle quality (only on poorly built & or tuned engines)
Large camshafts & or very tight squish make more difference
- Driving in traffic can become tiresome when combined with H/D clutch
- Difficult to show your friends

Hidden negatives
- Danger of flywheel fragmentation through excessive lightening of standard/inferior unit
- Too light, & F/W total mass (heat sink) is insufficient to prevent F/W face warpage through clutch heat

[JiMiH]

Does the type of lighter flywheel used differ from car to car?

What sort of flywheel would you be looking at for an R32 RB20DET?

[GTSBoy]

You could go for any type.

Lightened (shaved) factory ones give you the smallest decrease in mass along with potentially the highest risk of shattering and taking off your leg (didn't stop me doing it to my Alfa!!!)

Lighter brand new steel FW is safer and saves a bit more weight.

Alloy is possibly physically less strong, but saves the most weight, and is only mildly painful to pay for.

Basically you would do for an RB20 whatever you can afford....but most of them are already very throttle responsive, so for the street, the expense might not be warranted. If you were circuit racing it would be a different story.

cheers

[HoonBoy]

I've done ten's of thousands of kay's with a lightened flywheel and heavy duty clutch in Sydney traffic. You have to think more when doing hill starts and if you are cruising at freeway speed, you may have to change down a gear more often on the steep bits.

It reved out quicker and felt "sportier" to drive :rolleyes:

The only anoyance I had was if you raced into a corner and then stepped on the clutch for too long before going down a gear it would drop revs too quick and stall, it tought my mum how to clutch start the engine :)

It is something I would definetly do again.

[karl_2ltGC]

hoonboy, what motor?

[Forg]

Originally posted by Matty
Bill, just curious to ask - several people have said to me "don't go too light as you will lose low end torque" - but as a mech engineer I can't see how that argument possibly stands up, inertia is inertia and the less the better...
It's probably coming from people who're letting the revs drop off too much when changing gears or something; 'cos the engine's obviously going to drop revs more quickly.

A negative that Hypertune didn't mention, which I was warned about but can't prove or disprove, is that the engine may be harder to rev-match 'cos it's less apt to stay at a constant level of revs. That is, a car can become "jerkier" to drive.

[HoonBoy]

Karl, it wasn't a mitsu engine ;)

Forg, yeah my car was a bit jerkier to drive, especially if you were on and off the throttle at high revs, ie slowing down after a blast throught the lowere gears.

[Hypertune]

JiHiM,

The type of lightened flywheel differs from car to car.
In the same way engines & driveline configurations differ etc...
Unless you're a bofin with a knack for making things work, you need to use a flywheel that is specifically for your vehicle/engine/driveline configuration.
I've added two pictures of R32 Skyline flywheels that we sell...
The flywheel for the R32 RB20DET - it's a 4.8kg chrome molly unit.
It's the same weight as the R32 RB26DETT, yet it's not interchangeable.
Infact, they don't even look and cost the same... (btw: Retail is $924 AU)
http://www.toda-racing.co.jp/product/parts/flywheel/rb20det.jpg
Here's the RB20DET unit...
http://www.toda-racing.co.jp/product/parts/flywheel/rb26dett.jpg
And this is the RB26DETT unit...

[joshinthecity]

Great thread guys.

Exactly what this forum is all about.

Interesting questions, well answered.

j.