Light flywheel: Worth it?

[Evoluzione]

I'm coming to the conclusion that light flywheels are just a waste of money unless they are attached to an all out competition or track car. Here's my thoughts:

Does the engine rev any quicker? Does it make any more power? Is the car any quicker?

Ok, so you say it must because it has less work to do, but hang on, the engine is trying to pull (lets say on average) a ton of metal down the road, so is a (say) 5kg saving going to do much?

The lack of engine inertia cause three problems:

Difficult to set off from standstill, especially with a stronger clutch fitted

Idles rougher

The revs drop quicker in between each gearchange, does this last point alone work against anything gained?

My main question is this: Has anyone ever measured the effects?

[Evoluzione]

Thanks for all the replies on this, it's made for an interesting read and got some brain cells moving about a bit for me.

[Evoluzione]

andygtt said:

lets not forget a dyno is just a tool to establish one factor of performance which JUST measures power... and unless physics have just left the room, imo any dyno recording a 'bhp' increase for lightening a flywheel is clearly not measuring correctly and is surly just showing how variances can make it inaccurate?
Because Im pretty sure physics says BHP is a measurement of torque as a formula of the RPM its recorded at?.... and lightening a flywheel cant have any effect on these?

I can guarentee I can measure the effect of my lightened flywheel FAR more repeatable and accuratly..... I know how much it exactly cost and therefore the effect on my wallet... its FACT and REPEATABLE.... but meaningless in the context of my car going faster, but an important factor if i choose to miss-read the OP!!!

Like the OP I was actually interested in getting some useful discussion about whether a lightened flywheel is genuinely worth is and if anyone had actually got some measurable increases in performance from using one.... IMO by performance the OP was clearly asking for real worth car going faster 'performance'... Id take meaningful calculations over missleading dyno readings... but then i'm not the OP.

You're welcome to approach it from which ever angle you like, but I do think we're both looking at it a similar way or for similar results. Some background:
I generally build 2ltr turbo engines for 4wd cars, but my test hack is a fwd car. I use this because it's a fraction of the cost of the 4wd version and due to lack of transmission and different engine bay design it's a whole lot easier to work on when you're constantly changing things or doing tests for various things.

The engine is currently pushing out around 400bhp at a relatively low 1.5 bar, next stage will be wind it up to 2 bar and see what power figures are, not to actually push it down the road any quicker (it won't), just to see what it will put out so I can wave my willy around and it may get transplanted into something with a strengthened 4wd system.
At the moment it's pretty useless as a daily drive, high lift cams, very little in the way of restrictions in the air passages, horrible paddle clutch and of course a light steel flywheel.

Peak torque arrives at approx 4000rpm and it hits like a sledgehammer, 1st gear is useless, second gear is ok until 4k, in third gear it just about holds grip in the dry, but not a chance in the wet. It generally just pulls you all over the road and smokes the tyres, a car with half the power is quicker on normal roads, not on the motorway though when it really gets into its stride, but again (due to the traffic laws) pretty pointless. Even controlling the power on a track day is difficult.

Making the power is easy, it's harnessing it and making it road driveable that is more difficult, hence me pondering over making a heavier steel flywheel. It would help with the clutch take-up problem (along with a less vicious clutch) and may also take the edge off the lower gear shenanigans, but at what (if any) cost?

I guess some form of gear related boost control would be next on the list....