PassionFord - Ford Focus, Escort & RS Forum Discussion

It doesn't matter who said it was a complete waste, use your own brain.
A lot depends on what you expect and want from a lighter flywheel, F1 for example have NO FLYWHEEL.
A lighter flywheel is something that I have used on 70%-80% of the cars I've had, there is a VERY slight downside, with the lack of inertia, pulling away it will be more prone to stalling due to the lack of inertia, so 200-300 rpm more needed, and a slightly longer slip of the clutch, but seriously nothing that you would ever remember having to do when used to it, nothing at all different than getting used to another car you're using.
Another disadvantage of a lightened flywheel is when using hairy cams, the idle will be a bit lumpier, cams with more lift/longer duration have poorer cylinder filling at lower speeds due to air speed being slower so less efficient mixing of petrol air, so you will get a slight lumpiness, but nothing horrendous at all on a BD16, esp with modern ecu and mapping, the reason is the engine gives a kick every 90 degrees not linear over the whole 360 degrees.
If the engine was set up/mapped correctly you are really not going to notice anything that would worry you smoothness wise.
If you are concerned about the above then it asks the question how long does your engine idle in use, why are you bothering tuning and engine that spends it's time idling, ie working it out logically is it even 1% of the time idling stopping you from gaining benefits for 99% of the time ?
That's the downside, apart from the wallet hit of course, now for the good bits,
Less rotational mass allows the engine to accelerate faster, though it will produce NO MORE POWER, it will produce that power quicker, at idle it will rev up far quicker, and also drop far quicker, having no inertia(weight) to keep it rotating, think more 4 cylinder motorbike response from the throttle, it won't be as snappy as these but you get the idea, bikes don't use flywheel either.
The engine uses less fuel, with a lighter flywheel, as it sees less weight to lug around, the gearbox will have a easier time and last longer, when you are charging along and go to grab the next gear the revs don't "hang up" they drop quicker aiding gear changes, changing down a quick blip of the snappier throttle will also give a far better change.
Taking a standard 2wd cossie flywheel I weighed it at 8.9KG, the first lighten was to remove the massive section of meat on the reverse side of the flywheel by the ring gear, not all of it, but there is loads to remove SAFELY*, this took mine down to 6.6KG, so a very useful 2.3KG loss for around £30, so 2.3KG lost doesn't sound a lot does it ?
Picture the scene as a kid I used to play on the roundabout(playground one!!) I noticed that when my mates were near the outside edge of the roundabout it was so much harder to get up to speed, but when they were near the centre it was so much easier, it's the same with cars/engines just petrol powered not human powered, but this shows the importance of where the weight is taken from, the vast majority was removed from the outside right next to the ring gear, I don't have the formula to hand, but it is exceptionally disproportionate in weight removed from flywheel(where most are heavy around the outer edge) has a far far larger effect on the car than the weight lost from it.
Clutches wear better as don't have as much resisting force of a heavy flywheel trying to continue to spin as you're letting the pedal up, when changing down the slower flywheel/engine needs to accelerate to match the newly needed speed for that gear, less resistance is seen to this acceleration so down changes also get better, with less wear.
In short over my 27 years of driving would I use a lightened flywheel again, absolutely 100% without hesitation, and what I've had done to my sapphy.
Is there are time I wish it wasn't done yes is the answer, on my old celica RA28, I was running full race cams, twin 48's, "clockwork" ignition, it was a shit to drive below 4500rpm in town etc, where inertia would have helped to a extent, but wouldn't have been a patch on a correctly mapped ignition curve!!
It was all worth it though once out of 1 and 2nd gear, but could easily get down to 6mpg, and had a few flameouts from the engine/carbs!!
Sorry it's a bit long winded, but each to their own expectations, circumstances.
To give you an idea further slotting of my flywheel saw the weight drop to 5.8KG, all this was on the same bathroom scales, all with ring gear fitted, it could have been further lightened by drilling etc, estimated to be down to 3.8 to 4.4KG, but weigh up the costs!!
6.6KG just for an idea was the weight of a standard saxo VTS flywheel for example that i weighed, albeit on different scales.
Consider if you want performance 100% of the time you are moving, or want to sacrifice performance for a very slightly better idle, if all your car ever does is idle then you may want to ?
I seriously liked the way my RA28 idled angrily as I called it, gave it character, and would happily idle for the normal amount of time needed in traffic, but in q's was a pain in the rear as plugs sooted/got wet, but this wasn't the vastly better efi that we are blessed with now.
*SAFETY, avoid diy, unless of course you know what you are doing!!, and I would suggest ONLY using someone experienced in this, done incorrectly they can "grenade", horrific injuries are possible, even possibly loss of limbs, a chunk of flywheel weighing say 2KG has a lot of inertia at 6000rpm, and will and has gone through trans tunnels after exiting the bell housing, a "battle" between your lower leg and the chunk would be an easy bet.
Done correctly they are 100% safe however.
tabetha