Revving an engine before shutdown?

[Trotskyite]

Please bear with me on this one, I am slowly debunking a lot of the car myths I was raised on. I was taught to give a car one last quick rev as I turn off the ignition. I was told it primed the carb for the next startup, and I see the logic and how it doesn't apply to a more modern fuel injected car. Is there any benefit for any fuel system, or is it a flawed practice entirely?

[DARISC]

Originally Posted by Trotskyite

Please bear with me on this one, I am slowly debunking a lot of the car myths I was raised on. I was taught to give a car one last quick rev as I turn off the ignition. I was told it primed the carb for the next startup, and I see the logic and how it doesn't apply to a more modern fuel injected car. Is there any benefit for any fuel system, or is it a flawed practice entirely?

If you have CIS it's not a good idea because the large dose of unburned gas left after quickly shutting down after blipping the throttle will wash away some oil deposits that are better left where they are. Or so I understand it.

Another interesting question is "How to properly warm up my 911?", the answer to which is counterintuitive to many people's thinking.

[Trotskyite]

Okay, I'll bite. How do I properly warm up my 911? I can't be doing it right, it takes forever to get past the first hash for me. I'll be halfway to work before I feel confident in giving her some revs, and I have already missed my on-ramp opportunity by then

[Komenda Fan]

I've always been taught that blipping the throttle prior to shutting it down is detrimental to engine life, as Darisc stated. Shame, always so tempting to give it one last prod...

[Danny_Ocean]

[gigem75]

Even with a carbed car with an electric fuel pump a blip for gas for the next start is not necessary before shutting down. Why would would one want to wash down their cylinders with raw gas by bliping the throttle before shutting off the engine. I have always let the idle stabalize and let it gently shut off.

It was 28 the other morning and a few pumps before cranking she fired right up. Takes some throttle action to get the revs to 2k, let it run there for minute or less. When taking off there are a few pops after a 1/4 mile the engine is running fine and pulls great. Oil is obvioulsy not hot so that is the only thing that limits my application of throttle in the mornings.
70T Webers

[Steve@Rennsport]

Its a bad idea on every count as that leaves unburnt fuel in the cylinders and contributes to washdown and thats detrimental to piston, ring & cylinder life.

That practice is good for your mechanic's financial well-being, but bad for your pocketbook.

[slodave]

Eh, does the same apply for Motronic? My dad had that habit and transferred it to me. It's been done to this engine for 24 years.

[madmmac]

Seems like I read somewhere that with a sump system you are actually better off letting it idle for 20-30 seconds prior to shutdown.

[Wayne 962]

I hardly think that revving the throttle before you turn it off would cause any damage...

-Wayne

[DARISC]

Originally Posted by Trotskyite

Okay, I'll bite. How do I properly warm up my 911? I can't be doing it right, it takes forever to get past the first hash for me. I'll be halfway to work before I feel confident in giving her some revs, and I have already missed my on-ramp opportunity by then

Start the engine.

Let it idle for about 30 seconds while you buckle up, check your gages and mirror.

Drive off and use VERY LIGHT throttle (here's the part that threw me until it was explained in very logical terms by the likes of Randy Webb, Pete Zimmerman, Steve Weiner and a few others whose knowledge runs deep):

Keep the revs between 3000 + 4000 rpm until the temp is well on its way up.

Again, it's extremely important to do this using a VERY LIGHT throttle foot because asking a cold engine to deliver a lot of power is even more damaging to the engine than lugging it (which you are doing, to an extent, if you ask it to pull when cold below 3000 rpm).

There's an extensive thread about this on Rennlist.

There will be those who say Poppy Cock! Read the thread, consider all the sources, and I'll bet you won't.

Cheers

David

[Wayne 962]

It's okay, normal and proper to quickly rev the up and down a bit when trying to start up from cold - helps to get the fuel flowing in the carbs and MFI. For fuel injected engines with cold start - no need to touch the gas. For fuel injected engines with a hand throttle - pull it until the engine idles at about 2000 or so and let it warm up from there. It's also okay to drive with the hand trottle engaged until the car is warmed up, but this does put additional wear on your transmission syncrhos.

-Wayne

[Hugh R]

I've heard the same discussion for 35+ years. You rev the engine and shut down, you've burned the fuel in the cylinder. You crank the engine, and you have raw gas on the cylinder walls? After its been sitting overnight? Maybe in one cylinder that the intake and exhaust valves are completely closed, otherwise, I don't think so. Just how much oil do you think that gasoline is washing off the cylinder walls, and where would the oil go? Answer, sitting on top of the top compression ring!

Posted later, gotta agree with David, my old and now gone Aston Martin DB4 burned a quart of oil every 30-40 miles (I'm talking a lot of smoke) and when I pulled it apart, 5 of the 6 oil scraper rings and several other rings were literally broken in two. Cause, the previous owner would fire it up in sub-zero temps and roar off.

[Nickatnyt]

Originally Posted by Hugh R

Cause, the previous owner would fire it up in sub-zero temps and roar off.

Where in God's green earth did the PO live? Did this Aston have studded tires or a plow on front of it?

[jonbot]

There's this TV show named "victory be design" hosted by Alain de Cadenet, if you've never seen it, you have to, it's awesome. Anyways, I noticed every time he shuts down one of the cars he's just driven, he revs it up, then shuts it off while it's revved. This guy is a very respected ex-racer, and on the show he drives some of the rarest cars in the world. I've wondered for a while if this somehow benefits the motor, and this would line up with the idea of burning up the remainder of the gasses in the cylinders.

[Trotskyite]

Originally Posted by jonbot

There's this TV show named "victory be design" hosted by Alain de Cadenet, if you've never seen it, you have to, it's awesome. Anyways, I noticed every time he shuts down one of the cars he's just driven, he revs it up, then shuts it off while it's revved. This guy is a very respected ex-racer, and on the show he drives some of the rarest cars in the world. I've wondered for a while if this somehow benefits the motor, and this would line up with the idea of burning up the remainder of the gasses in the cylinders.

Exactly! I watched those last year and noticed the same thing. He doesn't do it on all cars either, leading me to believe there was a legitimate reason. We are talking cars worth millions too.

[old man neri]

Originally Posted by Trotskyite

Exactly! I watched those last year and noticed the same thing. He doesn't do it on all cars either, leading me to believe there was a legitimate reason. We are talking cars worth millions too.

Could just be for the camera. A lot more dramatic to rev it a bit and shut it off rather than just letting it idle for a bit. Besides, everyone loves the sounds of those cars.


As for start up, I noticed on my car when I start it when it's really cold (-15C) that I have to give it gas right away after start up to keep the RPMs up until the few misfires work there way out, it only takes about 15 seconds. It really does not sound happy idling at those temperatures right away.

[DARISC]

Originally Posted by old man neri

Could just be for the camera. A lot more dramatic to rev it a bit and shut it off rather than just letting it idle for a bit. Besides, everyone loves the sounds of those cars.

HA HA! Exactly my thought! Good T.V. show, eh?

As for start up, I noticed on my car when I start it when it's really cold (-15C) that I have to give it gas right away after start up to keep the RPMs up until the few misfires work there way out, it only takes about 15 seconds. It really does not sound happy idling at those temperatures right away.

Same with my SC intil the WUR kicks off in about 30 seconds.

..

[Trotskyite]

Originally Posted by old man neri

Could just be for the camera. A lot more dramatic to rev it a bit and shut it off rather than just letting it idle for a bit. Besides, everyone loves the sounds of those cars.


As for start up, I noticed on my car when I start it when it's really cold (-15C) that I have to give it gas right away after start up to keep the RPMs up until the few misfires work there way out, it only takes about 15 seconds. It really does not sound happy idling at those temperatures right away.

To be honest, it isn't a showy kind of revving, it seems pretty purposeful. Just a quick blip and kill. Is Alain a Pelican? Alain, we need an explanation!

[Mo_Gearhead]

Quote: "To be honest, it isn't a showy kind of revving, it seems pretty purposeful. Just a quick blip and kill. Is Alain a Pelican? Alain, we need an explanation!"
________________________

I ain't him!
But, this is a 'urban legend.'

Stop the car, apply the park brake, shut off ignition.
Done.