the way i understood it was, the lighter the flywheel, less load on the crank, thus freeing up more horsepower. recently i heard from a friend/engine builder that for boosted cars it's not good to have a light flywheel because it wont produce as much power because it's revving too fast. again i always thought, the faster the rev the faster you gain power.
so i have 2 questions with this being said.

1) is there any truth to that?

and 2) if this is not true, how light is too light? meaning what is the best weight to go with for a daily driven boosted car?

thanks in advance for the help.

 

The lighter flywheel purpose is 2 fold. It's not necessarily a Better/Worse ideology, more of a is-it-better-for-my-purposes thinking.

The amount of POWER has nothing to do with it in the long run. The POWERBAND is what changes with a lightened flywheel. When it comes to using a turbocharger, the benefit (or detriment) really comes with the turbocharger used, and how your driving style is. Yes, Lighter flywheels remove a lot of rotational inertia off of the rotating assembly, but there's a bit more to it than just a "weight saving" aspect.

When it comes to most of our smaller displacement engines, (under 2.0 litres), the peak hp that a car makes is really going to be in the upper rpm range, about the last 3K rpms, in which, unless you plan on driving that hard on a street on a daily basis, really isn't the point of POWER that you should look at. Instead, you need to focus on the entire range of power that you plan to make. Lighter flywheels can be a hinderance if your purpose is to not shift as often, and keep the power at a lower part of the band, which is the 3000-7000 range on most VTEC engines (this number generally is different with different engine applications, so this is simply an example.)
When you have a lighter flywheel, that is normally for NA applications, peak torque and power are in the upper band, and each faster shift that is made with the lighter flywheel keeps the rpms right at the rpm range to keep peak power and torque. The drawback for some people is that if you don't shift fast enough, the engine drops down faster OUTSIDE of the powerband, and you feel slower.

How does this affect turbocharged applications? It means that if the turbo car is outside of its powerband, the same thing happens. If the turbo is large, this means that it will take longer for the turbo to recover spool characteristics effectively. (For hondas, anything larger than a 60 trim, could POSSIBLY result in slower response, but that depends upon static and effective compression, displacement, final drive etc). Smaller turbochargers give a bit more torque than power, so imagine the result of something like a larger displacement NA motor. The lighter the flywheel, the faster it will fall out of its band if you don't shift fast enough. That being said, 8lb flywheels aren't that ideal, but 12lb ones, or stock for VTEC engines are just fine.


I personally went with a slightly lighter flywheel for my turbo road-race application. Some LS owners like to uses slightly lighter flywheels, especially if they use really efficient turbochargers with headwork. Most VTEC engines don't need it. Stock will work.


Modified by TheShodan at 6:44 PM 11/7/2007

 

thank you so much. what a great response. A++++