It might be a good time to talk to some Supra owners running a bit bigger turbos than the 14G or 16G and ask them about the slower spool-up of their T66 and T72 turbos and why they post slower ETs after the Fidanza flywheel installation.

Also, spool-up has nothing to do with peak horsepower or the amount of airflow of the turbo at the particular boost level - once the particular boost level is achieved. No matter if you hit 12 psi at 3.5K RPM or 4K RPM, 12 psi at 6.5K RPM is 12 psi at 6.5K RPM with the same turbo - no matter how you look at it, the turbo will produce the exact same amount of airflow, resulting in the exact same amount of horsepower. Even the faster spool up won't make the car any faster - unless one lets the RPM drop down to 2K between shifts. No matter if you hit 12 psi at 3.5K RPM or 4K RPM with the same turbo, if the RPM dropsdown to only 4.5K between shifts, the faster spool up as absolutely no effect on the performance (unless the full boost is realized at a higher RPM than the shift drop-off point - which is what may happen with bigger turbos).

If you think that lighter flywheel will produces faster spool-up, see how much boost and how fast you can build it by reving the engine in neutral or with the clutch disengaged. Since there's less load on the engine with the lighter flywheel - just like with the tranny in neutral, one should be able to hit 20 psi by 1K RPM with the clutch disengaged or the tranny in neutral, right? Yet, it's not somehow happening. Makes you wonder why guys with A/Ts are able to build up boost - and why guys with M/Ts are not... Maybe the load on the engine might have something to do with it...

Don't get me wrong here , I don't have anything personal against Fidanza or lightened flywheels in general , but the extremely exaggerated claims many people have come up with - such as "my engine revs MUCH faster", "my car is MUCH faster", "my car feels like a bike now", etc.

The engine with the lightened flywheel WILL rev noticeably faster only in neutral or with the clutch disengaged. Once the car is in gear, it's impossible to say that the engine revs 0.2 second faster to the redline in 1st gear, 0.3 seconds faster in 2nd gear and 0.5 second faster in 3rd gear. If the engine revs 1 second faster in all gears combined, the car would also be 1 second faster in the 1/4 mile because the RPM of the engine are directly proportional to the speed of the car - which means that the faster the engine engine revs, the faster the car accelerates - and I don't know of anyone who would knock 1 second off his ET and go from low 12's straight to low 11's only as result of installing the Fidanza flywheel (otherwise my flywheel would be made of titanium and weigh 2 lbs ).

As for the faster spool-up, turbos are spooled by exhaust energy that is not dependent on the RPM of the engine. Faster reving engine will not necessarily make the turbo spool up faster too. On the contrary, the less air-fuel mixture is needed to bring the engine to certain RPM, the less exhaust energy is produced in the process. If lighter flywheel and less engine load produced more exhaust energy resulting in faster turbo spool-up, rally cars wouldn't need anti-lag systems and the turbo would spool-up faster at part-open throttle than at WOT and full load. The reason why smaller turbos spool up faster than bigger turbos is because they require less exhaust energy to spool. If the amount of exhaust energey is reduced even further as result of less engine load - in form of part-open throttle or lightened flywheel, the turbo spool-up is going to be even slower.

However, lightened flywheel has a similar effect as weight reduction, aluminum driveshaft or lighter wheels due to less rotational mass, although the frictional losses of the drivetrain are still present and remain unchanged. Since the engine doesn't accelerate only the flywheel, but also the clutch, tranny, transfer case, driveshaft, rear differential, axles, brake discs, wheels - and the entire 3200 lbs mass of the car (in case of AWD DSM), the effect of the lightened flywheel might possibly translate to 100 lbs weight reduction. Can anyone tell that engine of 3100 lbs car revs faster than engine of 3200 lbs car once in gear? No. Otherwise one could also say that 1G FWD Turbo Laser revs the fastest - or faster than 1G AWD Eclipse because it's much lighter. Or are there any wizards able to tell apart a car with the stock flywheel from a car with the Fidanza, FWD from AWD or 12-second car form 13-second car just from listening to audio files?

In any case, the Fidanza and namely the ACT flywheel are also excellent safety feature for engines with higher-than-stock redline, where the stocker can't and shouldn't be trusted.

Here's a simple test for all the guys with stock flywheels planning to purchase the Fidanza: Invite a friend that had the chance to drive your car on several occassions over to your house, tell him that you just had the Fidanza flywheel installed, how happy you're with the purchase, how much faster the engine revs, how much faster the car feels and what not - just like many people say in this thread - and ask him to take the car for a spin to see what he thinks - and I guarantee you that he'll come back, confirm every single one of your words and claim that the Fidanza is the greatest shit since sliced bread - 'til you tell him that he drove the car with the stock flywheel. It's all in the hype.

Well, the truth is that once the clutch is engaged, the RPM of the engine are dictated by the vehicle speed in that particular gear no matter where the RPM may drop during the shift when the clutch is disengaged. The only time this doesn't apply is during the initial launch from a stop. While a lighter flywheel is going to be easier to accelerate due to less mass, a heavier flywheel will store more kinetic energy due to more mass.

The more kinetic energy the flywheel stores, the less horsepower it takes to accelerate it. The reason why one revs the engine to particular RPM prior to launching is storing the kinetic energy in the flywheel and the rotating assembly of the engine, as well as the rotating assembly of the turbo. A lighter rotating assembly will take higher RPM in order to store the same amount of kinetic energy. However, a lighter rotating assembly will also lose the stored kinetic energy at greater rate. Engaging the clutch during the initial launch is just like applying brakes on the engine. While a lighter car is easier to stop once the brakes are applied, a car with lighter flywheel is easier to stall as the clutch is being engaged. That's the reason why the clutch must be engaged at slower rate with the lighter flywheel than with the stocker and at higher RPM in order to achieve the same horsepower itransfer rate to the wheels and therefore also the acceleration rate of the car off the line. However, slower clutch engagement rate will also result in more heat build up.

If one puts a car with a lightened flywheel on a dyno - where accelerating the mass of the car is replaced by accelerating a roller of specific weight, one could see that even the HP gains are not proportional to the RPM or HP curve of the same car with the stock flywheel. While N/A cars will produce more HP in the low RPM range with the lighter flywheel and the gains will gradually become smaller as the RPM climb and HP increases, turbo cars won't even see such sigtnificant gains even in the low RPM range due to the fact that their turbos will spool up slower and their engines consequently produce less HP at any given RPM point during the turbo spool-up. With large turbos, the engine might actually lose more HP and torque in the low RPM range with the lighter flywheel than it will gain by reduction of the rotating mass - which, in case of high HP cars, may be actually desirable in order to make it easier on the drivetrain.

In any case, I don't entirely oppose lightened flywheels since they are, in fact, beneficial in particular situations, but the ridiculous hype, 40 HP increase claims, cars revving like bikes while being much faster than with the stock flywheel, etc. Most people install the lighter flywheels with aftermarket clutches - after driving with their slipping stockers, and rather than crediting the clutch for the performance gains they experience due to greater and better horsepower transfer to the wheels, they credit the chunk of aluminum. If someone claims that the Fidanza flywheel knocked even only 0.5 second of his ET of his 12-second car, picture what reducing the weight of each wheel by 10 lbs would do for him.