Hi all, I'm getting my clutch fitted soon before my map and i was thinking of getting a flywheel fitted at the same time whilst its all apart. After reading plenty of threads about some horror stories of cheaper types, machined oem wheel failing, running issues etc if they are too light... it all got a bit confusing lol.

I've been looking at the RCM lightweight flywheel which comes with everything ready to be fitted.

I'm just wondering if anyone has fitted one of these to a daily and can confirm they don't cause any issues like bad idle/hunting, juddering etc. The last thing I want is to fork out for this and end up having the original put back on!

My cars an 04 wrx.

Thanks in advance. Aaron.

 

I dont have a lightweight flywheel fitted but like you, I had been researching them recently as Im in the process of changing my clutch and flywheel. From what I have read (and Im no expert), it seems one of the most important factors is what the car is used for and how it is driven. For track use they are ideal as the lighter wheel spins up quicker so throttle changes are more responsive. Due to the flywheels reduction in weight, the engine revs drop quicker during gear changes but on a track, gear changes would likely be quick and engine revs always quite high. Drag racing they are not ideal as they lack rotation inertia at the initial pull off the line and need to get spinning. For daily driving they can be harder to get on with in traffic due to stop/start where the chance of stalling is increased. Pulling away is also different from the OEM wheel (unless youre pulling away like a race driver) as the engine needs more revs and more clutch slip to get the wheel spinning.

Personally I dont drive like a race driver everywhere, every day so my nanny gear changes would be effected as the engine revs drop quicker when the clutch is disengaged.

As for the technical stuff (again, Im no expert but this is what I researched) making the flywheel lighter can negatively effect the engine as it was designed with the weight of the flywheel at one end and the crank pulley at the other, it balances the engine. Reducing the weight at one end could disrupt this balance and alter the 'harmonics' I think its called and increase vibration and the chance of engine knock. Now some have said to change the crank pulley aswell for a lightweight one but apparently this will not 'rebalance' the engine, it will only make the harmonics worse.

IMO the flywheel and crank pulley are a certain weight for a reason, when the engine was designed all sorts of calculations and tests were made until they arrived at the correct weight for both items. You could argue a 'slightly' lighter wheel or pulley would have a positive effect due to tolerances but the lightweight flywheels and crank pulleys on the market are not slightly lighter, they are alot lighter. You may get some replies that say Ive got a lightweight flywheel and done 20k miles with no issues but that does not mean the engine is happy, I think poor harmonics can really effect the internals of an engine. Or, the engine really is okay and the Subaru engineers are useless lol

Basically, I went with a new OEM flywheel and Pink Box Exedy Clutch as Subaru use Exedy as standard (on the 2008 STI anyway) and its uprated from the OEM one.

 

Thanks for the reply. You've actually bought up a few points there that actually make a lot of sense. I think your right on the money. I have actually read stuff in the past about lightened crank pulleys, I think it was back when I had my evo... and they had actually caused premature wear to cranks/bearings due to extra vibration and harmonics. So I think my money will probably be better spent elsewhere!

Thanks again.

 

No worries, I'm sure many people buy lightweight flywheels and enjoy the benefits - again, it depends on the cars usage, track or road etc - but it 'could' potentially be wearing the engine. I guess if the car is for track use then the engine may be highly tuned and be overhauled/serviced so often that the need for a lighter flywheel out weights the increased engine wear.

Also for reference, I weighed a brand new Subaru OEM flywheel today, Im not sure if the same flywheel is used in all the Scooby engines so I can only speak for the 2008 2.5ltr STI Hatchback...

Subaru OEM Flywheel part number - 12310AA410 - 8.9kg

 

Interesting thread. I was debating getting some rcm pulleys the next time the belts need changing, but I'm re-considering now. My car is a daily drive and goes through a lot of traffic.

 

I had RCM pulleys fitted and TBH, it feels no difference to drive. But when replacing them, WOW! what an weight difference. I would say its 1/4th of the weight.

 

I had an ACT Streetlite flywheel on my previous car, little extra noise between 2.5 and 3k revs, but one of the best mods I did, have a Prolite to go on my blob now.

 

I have an API-supplied/fitted CC Stage 2 clutch and OEM lightened flywheel. Been going strong since around 2011.

However, I do treat the trans. with sympathy (always get the car rolling before mashing the throttle, etc.)

 

Both a lightened flywheel and rcm pulleys on mine, not a daily driver but have no issues driving it in traffic just needs a little more revs setting off