today i decided to be a ricer lol. i revved my motor and the rpms took forever to drop is this normal. in my old si i would rev it and it drop down fast. this seems like it just hangs there..

 

Our cars do that... I think it is an emission thing?! Maybe someone else can shed some light on it.

 

This is normal. It takes a while to rev down when you are sitting and just revving the motor up to a high rpm. We have all done it so no worries about feeling like a ricer lol

 

i believe its called rev hang? and i do believe it is an emissions thing

 

Pump the cluth pedal it tends to make the revs go down faster, at least in my exp.

 

wouldn't that be from the flywheel? the weight of it?

 

I thought the flywheel determined how fast the car revved up not down. Could be both, I'm sure someone with more experience will chime in.

 

Cool.

Some people seem to think it's the drive-by-wire throttle system making your lift from the gas pedal smoother. Others seem to think it's the lighter-than-typical flywheel.

Wonder what it actually is. Shall we take a poll? This is the interwebs, right?

 

Its our drive by wire system.

 

A lighter flywheel will typically gain and drop RPM faster. The speed at which the engine is decreasing RPM under no load is controlled by the ecu. It has a lot to do with fuel mixture, pressure across the turbo, and intake pressure.

Without getting too technical, its fine. If it dropped quickly, you risk a backfire anyway (exploding unburnt fuel in the exhaust stream rather than in the cylinder)

Most race/race style cars will have a light flywheel so the engine doesn't have to waste torque to spin the flywheel due to its higher moment of inertia. However, on a large vehicle, like a truck with a diesel engine and a low idle, a heavier flywheel keeps the vehicle from stalling, and also smooths out engine vibrations by acting as a mass damper for the rotating system.

 

Think it was Robevo that said the slow rev hang was controlled by the ECU to help completely burn fuel for emissions purposes, and that it could be tuned out to drop revs faster.

Dunno.. sounds good to me