Aztec Performance Ltd

iTrader: (234)

Am looking at either buying a light alluminium flywheel or have mine lightened. Whats the optimum weight for a road car?

Bob

BART!

The 4.2 kg Fidanza one has proved itself already....

LB4

I have read on here that 8kgs is the lightest you want to go for saftey sake.

Gary

Aztec Performance Ltd

iTrader: (234)

Options:

Exedy Billet steel ~4.5kg
Unorthodox Racing Alluminum ultra light 4.99kg
Fidanza 4.3kg
Toda Racing Chrom-moly 4.6kg

fuz

got a fidanza fitted on my bugeye no problems except for more

chrome

any more info about how 'low' you should go and why's and why nots?

Aztec Performance Ltd

iTrader: (234)

or original flywheel lightened to 7.5kgs.

Whats the weight of stock item anyway?

greasemonkey

Standard one is about 11kg as it comes. Speaking of which...

What you've probably heard is that around 8kg is a sensible lower limit for lightening the standard flywheel. There's no implication that purpose-designed lighter ones are inherently unsafe tho.

A lot depends on what clutch you have, how sensitive your left foot is, whether you do a lot of "town" driving and and so-on. Either way, if you get the oe fly lightened, it needs to be done at a place with experience and the willingness to warrant their work. Consequences of a flywheel disintegrating are not pretty!

crusher

Chrome,
As far as I'm aware the heavier flywheels help to smooth out engine speed variations...so you get a smoother idle and a higher reluctance to stall...the lighter flywheels give improved revability if you like..as there's less inertia and mass to move..so engine revs more easily..but the sacrifice can be a rough idle,and the tendency to need more revs from standstill...These tendencies are more exagerated the wilder you take the cam profiles for example...idle can become really rough..hence you then tend to idle at slightly higher revs to keep the engine running...

Aztec Performance Ltd

iTrader: (234)

GM: Glad you asked about the clutches....

1) SPEC Stage One High clamp pressure plate, steel-backed woven organic disk, bearings and tool. Ft/lbs of Torque 410

2)SPEC Stage Two High clamp pressure plate, segmented chatter-free Kevlar disc, bearings and tool. 470 ft/lbs of Torque

3) Unorthodox Racing Ultra G Stage 1 - Bronze Ceramic setups are an excellent choice for everyday drivers and weekend racers

4) RPS Max series clutch - This clutch can handle up to 445 ft/lbs of torque. This is one great clutch for street/racing use

Clicky:
http://www.subarustore.com/clutches.html


Have emailed them for model suitability. Unorthodox stands out.

Aztec Performance Ltd

iTrader: (234)

Lightened stock flywheel 7.5kgs for £85 but I think I'll go for an aftermarket one under 5kgs. Any thoughts on the different materials ie Alluminium, chrom-moly, steel?

stevebt

iTrader: (8)

i use a 7.5kg stock flywheel and its mint, was one of the best £ for £ mods ive done. i do know people who have lighter ones but in my opinion why go too light when the lightened stock flywheel is so good.

when i put the flywheel in and drove for the 1st time it felt like you needed another gear when you were at speed in 5th

CataIunya

I have heard from none UK modders that lightened flywheels are not recommended because of the lack of balancing in the flat 4 design, the heavier the flywheel the less the crank vibrates/moves etc any tuners comment on that ?

madou

I switched to Fidanza from standard, no issues at all, much improved pick-up, easier to control exact engine speed, heel and toe very easy

"I have read on here that 8kgs is the lightest you want to go for saftey sake."

Findanza flywheel is very well made, what do you mean by saftey ( sic ) ? I was concerned that it would be too light and impact stable idle etc, this has proved not to be the case

911

I think if you using this on the road 5Kg is ok. If you drive in competition on racing tyres then 8 is better. The mass of the flywheel will get you a more repeatable start.
On the safety side, a poorly machined '8' from a stock flywheel could burst at very high rpm, and you may loose some toes......
The professional '5''s as stated above should be safe as houses!
911

Aztec Performance Ltd

iTrader: (234)

911: cheers mate...cant put up with the blasted judder so am going for a lightened aftermarket fly and uprated clutch....then comes the TD05FE

Any ideas as to the different materials used for flys?

Bob

harvey

iTrader: (48)

My experience is basically in line with 911.
Standard fly wheel, or at least the ones I have weighed have been 11.9 - 12 kg. A competant machine shop will have no problem bringing this down to 8 kg and the difference is hardly noticable. It is still possible to get good launches with a degree of latitude and tick over is not affected.
Using a 4.6 kilo fly wheel from Roger Clark Motorsport and staying with standard cams made no difference on the road other than stalling the car frequently for the first few days until I got used to the new set up. On the drag strip however the lighter flywheel made launching a much more precise art and the new engine will have a heavier flywheel and clutch assembly.
In terms of value for money ie. bhp / £ a fancy flywheel is not good value and I cannot say that I felt any performance gain even with the 4.6 kg but I guess every little bit counts.

Aztec Performance Ltd

iTrader: (234)

Harvey,

I find that suprising that you felt no noticable gains. I thought that a light fly would result in a sharper throttle response and acceleration as the engine can turn the lighter fly more easily?

harvey

iTrader: (48)

I have no doubt that taking 4 or 7 kg away from the flywheel weight will make it easier for the engine to spin up but personally I could not detect the difference other than outlined above and thinking about it I do wonder if removing 7kg rotating weight will make a noticable difference to a 300 or 500 bhp or whatever engine.

easyrider

Its also got to turn the wheels and move a 1100kg+ car,i admit i cant preach on this as i have only driven a RS2000 with a waifer thin flywheel,but i fail to see there would be a great deal of difference apart from it reving quicker when not under load.It would definately be more noticable on a light car(Caterham ect)

But i do stand to be corrected though

easy

Aztec Performance Ltd

iTrader: (234)

Whats the general concensus:

Worth going lighter on flywheel?
Have std flywheel lightened to 7.5kg or will this risk 'bursting' at high rpm?
Buy aftermarket flywheel or is this really not worth the cost?
Stick with a std flywheel?

Bob

greasemonkey

Correct. However, it also, as Harvey says, makes launching a much more technique-critical operation. Thus there is a compromise between ultimate throttle response and acceleration, and giving sufficient margin for error that you don't compromise the performance of the car by stalling/bogging down off a standing start.

Of course if you don't compete with the car (or don't compete in circumstances where standing starts are absolutely vital) the priorities become slightly different, but even then you don't want to volunteer for a fly/clutch combination that starts to p*ss you off due to its jumpiness/stall tendencies when driving slowly around town.

Having seen the amount of material removal necessary to bring a standard fly down to 8kg or so, I'd be a bit reluctant to go any further. Even so, as mentioned further up, this job, if you have it done, needs to be done by an experienced firm as you don't want to have to deal with the consequences of a failure.

There definitely are worthwhile gains to be made from running a lighter 'fly, but both it and the clutch need to be considered as a unit. It's all very well getting a 4.something kilo one, but if you matched it with a paddle clutch for example, you may not find the result easy to live with.

kevin stanton

i'm running 6.8 with no problems

StickyMicky

ive posted on this a few times and i still dont have a clear answer in my head, would a lightend flywheel make your car quicker down the strip, in real terms, i can compleatly understand the sitting there out of gear reving thing, but as posted above, when you drive you still have to drive the gearbox and wheels etc etc

so i cant see any gains to be had, considerd this for a while, but ive yet to see any hard evidence to sugest that its a positive mod

911

As an ex drag racer and current hill climber these are my personal thoughts:
In competition, the starts are absolutly critical, especially speed events such as the above.
The 8Kg+ flywheels give the engine the ability to over come the mass of the car/tyre grip to launch the car off the line with the MINIMUM risk of stalling/bogging. The variation in start line surface/weather/driver/engine temperature/Intercooler etc etc etc is huge, the 8+ f/wheel helps overcome these real variations and still get a good start, every time.
The 8- f/wheeels have far less capacity to overcome the variables, so the driver must be far more accurate at summing up the conditions and still get a good start. This is MUCH harder than it seems.

When you are off and away from the start, the engine has to accellerate the car (and the flywheel). If the 8+ is fitted, it will take more of the engine to build revs compared to an 8- f/wheel, BUT, against a car weighing 1200Kg the difference is about 5Kg in 1200. However, the 5 Kg is at the engine and the other mass is via gears etc, and I can't spend the time rationalising that lot mathmaticaly nowadays!
OK, you are now read to change to 2nd gear, the flywheel is revved-up and you change gear fast, the engine speed does not drop much (I said change fast!) if you have an 8+ wheel, it is full of energy, so off you accellerate again. If you have the 8- wheel then this is where you may gain (back to the 5Kg in 1200 ratio again). And so on...
I believe that the control you get in achieving consistant starts with the 8+ wheel outweighs the snappy throttle responses in gear shifts. But, just to add a little more:
On a hill climb you do one killer start, and then may be 12 gear shifts. On a rally you do one ok start as you now have a zillion shifts to make to catch-up the time with. The start is nowhere as critical.
So, for the raod and added fun/pub chat/interest go for the 8- wheel, for serious competition stick to the 8+ wheel as you need every 1/100 second you can find!
Whew, 911

Aztec Performance Ltd

iTrader: (234)

Cheers guys. V informative. Have eliminated going for an aftermarket flywheel.

Can get a 8kg lightened stock flywheel from Alyn@ASPerformance.com for £85 or purchase a secondhand stock skimmed flywheel for around £50.

911

Go for the 8kg, make sure the clutch surface is smooth and true and enjoy!
911

cong

ive got a lateral organic clutch and lateral lightned flywheel weighing 6.8 kg and it pick up really smooth and faster then a oe flywheel and picks up better at higher revs

highlander68k

I read somewhere (probably on here) that an 8+ flywheel is better for the likes of quarter miles runs due to the fact that the inertia of the heavier flywheel prevents the engine speed dropping too quickly during a gear change. The lighter flywheel is not as good on quarter miles due to the speed at which the rpm drops during the gear change.

This sounds logical, but due to my lack of engineering and physics degrees, I cannot back this up.

I can say though that with a 4.5 kilo flywheel and an AP organic clutch setup, it does seem pretty good on a good thrashing session (compared with standard). As an example, running my 94 wrx at santa pod with less than .5 bar of boost, I managed to get a 14.00 quarter mile. This was running a standard 240 ecu map, about half the boost I should have had (due to electronic boost controller problems). This was where other similar wrx's were getting 14.5 and 15 second runs - although there were many getting 12s and 13s

Aztec Performance Ltd

iTrader: (234)

Doh....after all that I fell in love with a Fidanza flywheel and bought it

About 4.2kg I think...lovely piece of kit.

Looking forward to having it fitted (along with many other goodies)

Bob