Revving an engine before shutdown?
 

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.

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 :)

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...

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

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.

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.

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.

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

-Wayne

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

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

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.

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

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.

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!

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.

A lot of cars with turbos here in sonyland (aka Japan) have "turbo timers" (after market accesory) that let the car idle for a good 5 minutes or so before they shut down on their own. Of course, by then the owner is either in their house or some resturant.

We also do the idle before drive routine over here too.

Now ... I tend to think that warming the car properly before driving is a probably a good idea but ... I don't seem to see too many folks gunning their cars and killing it too. Come to think of it, I don't see the kids on the mountain passes nor the Skyline GTR folks doing it either. Rather they let the car cool down before the kill the ignition.

hmmmmmmm

I bought a Callaway VW Rabbit years ago, and the owner (who worked at Callaway as well) told me never to rev a freshly started turbo motor...ever...until it was at operating temp. That was about the only thing he told me not to do with that car. Remembering now, that was very fast.

Should never have sold that car :)

I've come to believe that idling the motor when cold is the worst thing you can do - oil is thick and sluggish, and the flow is the worst it'll ever be. I always run @ 2,000 RPM until the internal engine thermostat bounces open a few times in quick sucession (90 seconds, 2 minutes - you can't see it do this with a 5 bar oil pressure gauge), and then drive it, keeping revs down and load light until the oil is up to temp. The owner's manual says to not idle the motor to warm it up, too.

I was always told the theory behind the "blip and shut down" was to get a spurt of oil flow to the top end, but I was also told the contra-theory about washing the oil off the bores.

Turbo cool-down procedures are a different beast again, especially when you don't have to drive through your neighborhood off-boost for 3-4 miles before shutdown.

The factory put a 10-30 second "turbo-timer" that cuts fuel but keeps the ignition running on the 930's, apparently to burn off as much fuel as possible and keep pumping oil through the turbo bearings even if you switch the key off whilst it's red-hot...

Some folks do the fast-idle thing on shutdown on 930's to ensure that the turbo scavenge pump gets its act together, and swear by it. I find that mine will puff oil on startup when it feels like it, regardless of what you do. :)

I'd bet if you took 2 identical cars, did the quick blip-and-cut-off thing with one and not the other, you'd see little or no difference between the two that you wouldn't see otherwise.

With a CIS fuel injected engine the fuel would be switched off as soon as you kill the ignition. Therefore I would expext LESS fuel to be present in the system as the engine would have tried to suck it out of the lines.
With Motronic I would have thought the injectors would have stopped pulsing when you switch off and again I cant see a bore wash issue here.
Carbs a different story entirely

I've always heard the reason for the blip was to build oil pressure to insure everything is well-coated with oil while the engine is off.

Personally, all of this is bunk. Rates right up there with Harley owners that think it's necessary to rev their engines at every stop light.

Just turn off your engine. If it was important to rev your engine, it would be in the owners manual.

Real simple, isn't it? :D

And, re start and go, the owner's manual does say "start and go" (garage warmups are bad).

Some strong opinions here.

As I have been told over the 40 or so years I have been around cars, trucks and farm machinery, the process of shutting down might be of some benefit to the engine, depending on the type of engine. The process never involved "blipping" the throttle, rather gently raising the RPM a little and then cutting the ign/fuel while there was still some oil pressure. If the engine uses a carb and the butterfly is nice and tight, some oil will be sucked onto the valve stems and piston rings. Diesels will do it too since the fuel cutoff IS the switch. The key is there must be a good vacuum or nothing happens.

Some of the statements here are as ignorant as the myth itself.

Always enjoy your posts, Milt (even though you haven't posted very often here) - would be fun to read your comments on, or at least a list, of the ignorant statements. :D

+1

And warm up procedures are in there with that too. Here in CA, the engine is pretty warm to start with. If you stay away from WOT redlines for the first 10 minutes after cold start, that's about all that matters.

I had neighbors once who would sit in their running truck and SUV for at least 3 minutes before starting to drive. It was nuts, especially because they would always get a new model within 2 years. ;)

George

Revving an engine before shutdown is one of those myths like:

"You have to come to a full stop before re-setting the Odometer" :rolleyes:

Or: "KN filters increase HP" :eek:

Any others? :(

We should have a "Myth-list" on PP. :D:D

I would think on turbo cars its very bad because you dont want the turbo spinning at 30,000 rpm when you cut the oil to it. As for starting and imediatly driving off i find the car warms up much quicker when its sitting still and fresh air isnt being blown over it. But i dont follow any sort of regiment as far as thats concerned because there doesnt appear to be a definitive way to do it

As a long time Triumph man, I can tell you Harley owners do that to keep the engine from quitting. They may never get it started again. :)

I was hoping someone else would answer this, so I wouldn't have to give away my age.:D

Some of the muscle cars we had in the late 60's and early 70's had run on problems. Probably due to some combination of high compression, advanced timing, lean idle (for smog in 70's), cheap gas, and a hot motor (as we always ran em hard all the way to wherever we where going).

So when we pulled up at our destination; we just blipped the throttle & cut the ignition. This sent a rich gas mixture into the engine, which prevented the run on (i.e. dieseling). If you didn't do this, some of these cars would sit there and diesel for about 20 seconds (pretty embarrassing).

Some cars got around this by putting a solenoid on the throttle stop. When you cut the ignition, the solenoid would deactivate, allowing the throttle to close down all the way.

Hope this helps as I'm feeling old now...:p

Engine rev with the vehicle at rest can only occur with the ignition ON. Whatever happens before ign. ON is different from what happens after ign. OFF (engine can't rev with the ign. OFF).

Opening the throttle introduces more fuel into the intake. Ignition OFF immediately after this event will leave excess hydrocarbons (unburnt fuel) in the chambers. Not good for long term cyl. wall lubrication.

The racey rev from Cadenet's on-camera shutoff procedure is of no consequence to most of us - it's not his car anyways, but repeated practice is bound to have a cumulative effect.

YMMV .... with throttle blips. :)

"So when we pulled up at our destination; we just blipped the throttle & cut the ignition. This sent a rich gas mixture into the engine, which prevented the run on (i.e. dieseling)."

I remember the symptom well. It happened on most early emission-equipped vehicles. The richer mixture probably cooled the chamber parts just enough to raise the preignition threshold.

Sherwood

Those who warm up by idling are heading down the wrong path. It's well known that you should never do this, cold....even noted in the manual. I never touch the gas pedal at startup, either. It's about 30-60 secs of idle (get to hear my sold throwout bearing rattle)then she's on the road.....never lugging her in any way and keeping the RPMs around 3K,..(usually 3rd gear for a while, once on the backroads....). Once I see around 150 degrees F, then we invite 4Ks (but no higher). THEN, when operating temp is hit, we dance well upward on the RPMs! Usually at 10-15 minutes on the backroads, I'll see around 150 degrees (during this southern winter) then at the interstate entrance ramp ramp, we start generating some real heat!

Just standard operating procedure for me (and her).

Blip? Nadda...........

Best,



Blipping the throttle just before shutdown (on a 911) is not something I would do, at all. (WTF?) I let her settle for about 30 secs and turn her off.

Forgot to add an opinion about cold starts. If one is from the, "let the car sit until the engine is at operating temperature" camp, then what about the other lubricants in the vehicle? Don't they get an equal chance to warm up too? That includes gearbox, wheel bearing, steering box, etc.

If the engine has modern emissions equipment (i.e. catalytic converter), in order to reduce emissions (greatest at startup), starting and driving is quickest way to bring the cat up to temperature.

Sherwood

Gunter - DONE!

i always thought it was a racer's practice to combat fouled plugs...