You guys worry to much.
Better to REV engine before shutting it off
- Thread starter TallPaul
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unless you have an accumulator to charge, revving the engine before shutdown is a waste... at least on a piston engine it is, i don't know anything about rotaries.
keep in mind, raising the throttle at idle will momentarily cause a significant drop in vacuum followed by the RPMs jumping up and vacuum rising as well.... it's entirely possible that by revving it up you can actually generate more vacuum... especially if you have a lumpy cam where vacuum at idle sucks(... bad pun).
keep in mind, raising the throttle at idle will momentarily cause a significant drop in vacuum followed by the RPMs jumping up and vacuum rising as well.... it's entirely possible that by revving it up you can actually generate more vacuum... especially if you have a lumpy cam where vacuum at idle sucks(... bad pun).
Reving the engine before shutdown was a battery charging thing we did back in the 50's after turning off all lights and things with our weak generators.
Doing it actually leaves unburned fuel in the cylinders, washing the oil off them and down into the oil. You will lower your oil viscosity, deteriorate the additives, and have more wear on startup.
Doing it actually leaves unburned fuel in the cylinders, washing the oil off them and down into the oil. You will lower your oil viscosity, deteriorate the additives, and have more wear on startup.
^^^Not true at all in a modern automobile.
Maybe on something with a carburetor, but it's just not happening on a fuel injected vehicle.
And those 'weak' generators actually burnt out headlights for many of us who revved them too hard at night! I can still hear my Dad yelling to keep the revs down after dark.
Maybe on something with a carburetor, but it's just not happening on a fuel injected vehicle.
And those 'weak' generators actually burnt out headlights for many of us who revved them too hard at night! I can still hear my Dad yelling to keep the revs down after dark.
Originally Posted By: RobertISaar
unless you have an accumulator to charge, revving the engine before shutdown is a waste... at least on a piston engine it is, i don't know anything about rotaries.
keep in mind, raising the throttle at idle will momentarily cause a significant drop in vacuum followed by the RPMs jumping up and vacuum rising as well.... it's entirely possible that by revving it up you can actually generate more vacuum... especially if you have a lumpy cam where vacuum at idle sucks(... bad pun).
Yeah but the amount of extra blowby created by the sudden rev will never be removed by that little increase in vacuum, plus I don't think anyone is talking about a rumpy cam that idles 11" of vacuum...
unless you have an accumulator to charge, revving the engine before shutdown is a waste... at least on a piston engine it is, i don't know anything about rotaries.
keep in mind, raising the throttle at idle will momentarily cause a significant drop in vacuum followed by the RPMs jumping up and vacuum rising as well.... it's entirely possible that by revving it up you can actually generate more vacuum... especially if you have a lumpy cam where vacuum at idle sucks(... bad pun).
Yeah but the amount of extra blowby created by the sudden rev will never be removed by that little increase in vacuum, plus I don't think anyone is talking about a rumpy cam that idles 11" of vacuum...
^^^Agreed. And on my street toy I do have an accumulator that holds a lot of oil.
No revving required, it fills the second you start the car and stays filled the entire time it is running unless some truly epic driving event is generating some outrageous g's!
No revving required, it fills the second you start the car and stays filled the entire time it is running unless some truly epic driving event is generating some outrageous g's!
the way i've seen a lot of people with really high-dollar engines do it is to rev the engine for a few seconds on shutdown to get the oil pressure up to fill the accumulator, then close the valve feeding it, let the engine idle, then shut it down.
then on startup, they open the valve just before cranking to build oil pressure before they engage the starter. after that, they leave it open so that it will do it's job of "buffering" the oil supply until they pressurize it for shutdown again.
i would think it would work quite well.
then on startup, they open the valve just before cranking to build oil pressure before they engage the starter. after that, they leave it open so that it will do it's job of "buffering" the oil supply until they pressurize it for shutdown again.
i would think it would work quite well.
Originally Posted By: L_Sludger
Am I dreaming, or did TallPaul actually make this thread?
I couldn't help myself. It has been a lot of fun discussing this absurd topic.
Am I dreaming, or did TallPaul actually make this thread?
I couldn't help myself. It has been a lot of fun discussing this absurd topic.
My mother in law (who lives with us frequently) does this every time she parks her 4 cylinder Nissan truck. She parks in the garage since we are not supposed to have pickups in the driveway (gotta love the HOA's). From in the kitchen we hear VROOM-VROOM-silence. She revs it to about 4K twice in a row and turns off the key at the peak of the second rev.
I have suggested to her that it is pointless, my wife suggests that I choose my battle wisely.
I have suggested to her that it is pointless, my wife suggests that I choose my battle wisely.
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