Lightweight vs OEM flywheel for FI
 

In anticipation of installing my turbo kit a few months ago, I installed a clutch and at the same time, went with at 12.8lb flywheel. I immediately noticed more response from the engine, quicker revs, etc - it definitely improved the feel of the car.

Now after going FI I'm having some issues with the new clutch and I'll be replacing it soon. I'm curious to hear some opinions on whether to stick with a lightweight flywheel or to go back to the OEM. I've read conflicting opinions, with some people saying the lightweight flywheel doesn't offer the same benefit on a turbocharged car, and that the turbo will spool faster with a heavier flywheel due to the increased load on the engine. Would this faster spool be cancelled out by the fact that it takes more work to actually spin the flywheel?

Any real-world thoughts/experiences here? Thank you!

I would normally consider them exclusive for purposes of assessing benefit factors. That plus your clutch selection may limit your flywheel options. The increased initial load on motor to get the drivetrain moving from a heavier flywheel can be countered in the ignition timing and proper tune for the FI application alone. The overall benefit of a lighter flywheel for a sports car is definitely there, more so than found within alternative FI applications for towing, offroading, etc. I also don't believe you're concerned with mpg after going FI...

I went with a streetlight not a prolight. Sometimes I think my clutch heats up to fast even with a streetlight and having a lighter flywheel that may not be able to dissipate the heat more than a heavy flywheel with more mass may not be in my best interest for a Day to Day driver.

One thing for sure is, get Cusco motor mounts. It's a HUGE must. My engine had so much play with the factory mounts it was crazy. The factory motor mounts with 300RWHP likes to roll in mud like a pig in shit.

I have the same clutch/flywheel setup as you, and it's what's been giving me problems. It was perfect for the first 3000 miles, but then began dragging, locking me out of gear at stoplights, as well as slipping badly sometimes - especially starting on an incline. Slipped badly when I tried to pass someone in 4th gear on a back road today too. I've been considering an Exedy Stage 2 clutch, but the revised version uses the OEM flywheel and a lightweight Exedy flywheel is pretty pricey. Could stick with ACT but I'm nervous after seeing this clutch give me problems so quickly. Decisions.

But I hear you on the motor mounts - I'll be doing the Perrin mounts, as well as some transmission/shift bushings when we get in there to see what's going on with the clutch. LOTS of slop in the drivetrain at that power level for sure. I can only imagine what it's like for the guys with 350+ tq.

How is it that you upgraded the clutch and are still having issues? What issues are there, slipping still?

Usually, aftermarket flywheels accomplish the weight reduction by changing material not size, i.e. steel to billet aluminum, though i have no idea what the oem flywheel material and thickness is, and if oem has that treated finish layer to reduce vibrations, etc. While they are likely physically smaller in thickness as well, I wouldn't assume that you need that mass to combat heat on a daily drive. Biggest drawbacks should just be increased NVH and reduced mpg. Some people might change gearing or ignition timing and anti lag tunes, but never heard of switching to heavier flywheel for turbo spool...

Oh damn, I'll have to be sure to avoid those clutches. Sounds like oem would have held up better, sorry man!

Yep - that's exactly why I'm asking - I've read the turbo spool thing on different websites, but I've never actually had me tell me that they did that in practice. I love the way the ACT flywheel made the car feel (and I loved the clutch too at first lol) - this decision has more to do with the decision of which new clutch to go with/how much I want to spend.

honestly, your wasting your time thinking about this flywheel
its means nothing in terms of gains.. its a very gimmicky mod

if its causing your problems now swap it out for stock

going FI changes everything.. and with that a huge list over other headaches.. so be prepared for that

I am having the same bs clutch / shifting problems with the same act setup on my girlfriends car. I sent my first one back to see if somthing was wrong with it. I got a 2nd one in the meantime and started having the same issues in less than 700 miles. I did all the standard things to adjust, bleed and replace. But it barley helped. As far as the lighter flywheel goes. It was great when she was na. Now with the supercharger, it has had the occasion to stall when creeping in a drive trough or in stop and go traffic. Some may be tune related and it's worse on e85.

Headaches for damn sure. If going FI expect to dish out 10k+ for a real tune, turbo kit and all the supporting mods.

Stay OEM. Having your car sound like a broken POS isn't worth the gains, when you won't notice them anymore after a week of driving. Chatter Chatter Chatter

I have zero chatter with a disc clutch and streetlight flywheel. Now I had a puck clutch with a prolight flywheel once and holy crap! Going through the McDonald's drive though sounded like I was throwing a rod bearing with my foot off the clutch peddle and no gas.

While it's not a FR-S or BRZ I have done the boosted and lightweight flywheel combo before.

I ran a SPEC lightweight flywheel on my 99 Saab 9-3 with the OEM Viggen clutch disk and pressure plate combo running 18 PSI on a TD04-15T. There are a couple things that will cause your car to stall in the first few days of driving until the auto adapting feature of the ECU adjusts for when the engine has accessory load being placed on it while at a stop or coming to a stop (a/c compressor and radiator fans). The other option you have is to get a custom tune to take care of the base tables and not need an adaption period.

You'll notice your revs drop much quicker in between shifts so you'll need to watch for that when going back into gear. You'll be a little more bogged down from a dig until you get used to holding your RPM a little higher to get going from a stop. After all that it's nothing but positives, especially when you get your turbo spooling. That reduced mass will translate into a faster acceleration of the motor.

So it's not that there are negatives so much as it is minor driving style adjustments. Now in terms of clutch I never played around with puck style clutches. If you have concerns about your clutch bite and feeling on/off with the clutch stick with an OEM disc style clutch with a slightly more aggressive bite and a higher rated pressure plate for better clamping load. This will help you have a more OEM feel with the clutch.

I think there is some confusion regarding what I'm asking here. To clarify the situation and my thought process:

-Car is already turbocharged with all necessary supporting mods including oil cooler and ACT clutch/lw flywheel. Everything is tuned by Moto-East and running beautifully.

-Money is not the issue here, and I'm not some dumb kid that doesn't understand how a lightweight flywheel works.

-There were no issues with the flywheel whatsoever - I love the way it made the car feel. Even after turbocharged, any stalling issues were eliminated through tuning.

-Now after only 3000 miles, the clutch is giving me problems, and I want to switch to a different clutch. Once of the ones I'm considering (Exedy Stage 2) uses the OEM flywheel rather than a lightened one.

-The question was whether or not it made any sense at all to go back to an OEM flywheel after already upgrading. The ONLY argument I have ever read toward a heavier flywheel, is that the turbo may spool a bit faster due to the increased load on the engine.

-If I wouldn't notice the difference switching back, the I would use the Exedy Stage 2 and go back to the OEM flywheel.

From the responses here, it seems that there is enough of a difference, and it makes sense to stick with a lightweight flywheel and appropriate clutch - so this is what I will be doing.

Thanks.