dangarza

Along the same lines as the post about the "cooldown" period (useless for NA engines):
I've seen some guys "blipping" the throttle (perhaps to 2,000 or 2500 rpm) and then immediately shut down the engine as the revs are still coming down.
Is this a Good practice? Bad practice? Useless?
Anyone care to comment on the "physiology" of doing this? (Forcing a few piston cycles with no combustion, I suppose?

Daniel

Siepel

Hi Daniel,

I'm not sure about N.A. engines, but I follow a 20 second idling before shutdown as a good practise coming from turbo engines.

You need to idle about 20 seconds or so to ensure that the turbo parts (vanes etc.) are rotating at a minimum speed before shutdown. If you don't do this, after shutting down the engine the oil pressure will be Zero, but the turbo will still be spinning hard, causing excess wear in the bearings (as there is no pressure for an oil film anymore).

In the case you discribed there should still be oil pressure (as the engine itself is still rotating), but maybe (because we don't have direct cylinder injection) there could be a bit of unburned fuel in the inlet channel, no ignition anymore, sucked through the engine and destroying the catalyst because it ignites in there (the latter is an uneducated guess however).

Hope this helps a bit!


Siepel

slalom44

I recall years ago some people used to blip the throttle with cars that had carburetors to make it easier to start. If the check valve by the fuel filter did not work properly, the fuel line would empty back into the fuel tank, leaving the fuel line full of air. You still had fuel in the reservoir of the carburetor (I believe it was part of the accelerator pump), but an empty fuel line meant that you had to crank the engine for a fairly long time to get it started. Blipping the gas would give you a little extra vapor in the cylinders with a cold engine, therefore requiring less cranking to get it started.

Electric fuel pumps in modern cars eliminate this problem. Theoretically, I can't see any benefit to blipping the trottle since the car has a fuel-rich start already. But this practice will leave excess unburnt fuel in the catalytic converter. The S2000 has a preheater for the converter that burns the unburnt hydrocarbons during startup to bring the converter to operating temps faster. I would guess that flooding the system with excess fuel could possibly reduce the life of the converter since it wasn't designed to take this extra fuel. You might also get the smell of gasoline if you parked your car in a garage.

Gernby

I wouldn't do this. Who wants to look like a punk ricer boy every time they cut the car off.

dangarza

Thanks slalom 44. I like your answer. Not that I've ever done it, (Not even years ago, on cars with a carburetor) but it was being done by a guy who drives collectible cars. (with no fuel injection or catalytic converters, for sure). Your answer makes sense.
Thanks
Daniel