Is a little rev a good thing?

anaxemurderer · Post by **anaxemurderer** » Wed Feb 11, 2009 10:59 am

I've always been told that its a good idea to give my V8 a little throttle blip before i turn it off. Something about helping to clean off the plugs. Obviously I don't have a turbo or anything, its a fairly standard rover 3.5 on carbs.

Is this actually true?

Nick

topcatcustom · Post by **topcatcustom** » Wed Feb 11, 2009 1:02 pm

Wouldn't have thought so unless it has been left idling for a while before you turn it off, obviously not a good idea on a turbo as after the engine stops the turbo is still spinning at 150000rpm or something ridiculous and no running engine= no oil for turbo bearings!

kiwicar · Post by **kiwicar** » Wed Feb 11, 2009 1:10 pm

It's a one of those old wives tales, no reason to do it appart from it sounds nice. Been around for years, was said to be good for all engines at one time or another. It ws said to be good for FS1Es when I was at school, "because the oil injection puts an extra squirt of oil vepour into the cylinder, this stops rust forming on the bores while it stands overnight" I think there is a word for this, but people believe it anyway.
Mike

CastleMGBV8 · Post by **CastleMGBV8** » Wed Feb 11, 2009 1:23 pm

Third opinion, no just a waste of fuel. not only what you burn when you blip the throttle but with a carb engine there will still be fuel sucked in on the overrun when you switch off, and this will wash the oil off the bores causing more wear.

Off course I used to this just to here the lovely exhaust note of my modified MG Midget, but that was many years ago

FWIW

Kevin

Ian Anderson · Post by **Ian Anderson** » Wed Feb 11, 2009 1:42 pm

Ok Technical reason
People consider aircraft engines to be highly maintained etc and what is good on them "must "me good for the car?

Well
In a plane (Light aircrft / cessna type) the normal procedure is to run it dry of fuel by switching off the fuel pump.
As the fuel in the bowl runs out the mixture leans out and causes the revs to rise just as it dies!

So people thought it must be good to rev the engine just before turning off.

Well no - unless you use the same method by running the carb dry

I'd also agree that the bore wash would not be beneficial

Ian

ramon alban · Post by **ramon alban** » Wed Feb 11, 2009 2:13 pm

Ian Anderson wrote:So people thought it must be good to rev the engine just before turning off.

Well no - unless you use the same method by running the carb dry

Hello Ian, I know its not the same as the OP asked re Carbs, but with my Efi Vitesse from Day 1 in 1993, I have habitually raised the revs gradually to something non-destructive (say 4000 rpm) prior to parking up and then switch off the ignition immediately.

The gradual throttle movement does not fire the ECU acceleration circuits so the mixture in not enrichened.

My perception is that the slightly extended period of high rpm (a slow blip if you please?) raises the oil pressure nicely to pump some extra lube round the system and because the ignition is instantly OFF, then the injectors can NOT fire any fresh fuel into the bores and I get the best of three worlds.

# Extra lubrication into all the crooks and nannies - and

# No fuel around to wash it off - and

# Less friction and wear on the next cold start.

What do you think?

CastleMGBV8 · Post by **CastleMGBV8** » Wed Feb 11, 2009 2:59 pm

Ramon,

Can't see any problem doing that with EFI because as you stated no fuel will be injected with the ignition off.

I doubt that you get any extra benefit by revving to 4000RPM there has got to be sufficient oil pressure at say 1500-2000RPM to give the element of protection you are suggesting, bearing in mind that the Buick/Rover engine was designed to work on volume rather than absolute pressure in the pre crank driven oil pump engines, the later ones are not that different, just a more efficient oil pump.

Kevin.

Ian Anderson · Post by **Ian Anderson** » Wed Feb 11, 2009 3:07 pm

Ramon

You got me there.
Now when the ignitionis cut what does it do? (All the electronis skulduggery!) If it first cuts the spark and then the fuel pump and ecy possibly correct but with the whole lot cutting together my thinking is you would be injecting more fuel than at idle and this would be left in the inlet and eng up washing the bores. How much damage will be done in reality - probably not a whole bunch!

The extra oil might be a good thing but if you are that worried why not run an upper cylinger lubricant (Castrol R is my favourite!) give that historic racing smell and nobody can figure from where it comes!

Oh and if you run turbos I believe the correct shut down procedure is to run the car at idle for 3 - 5 minutes before shutting down after hard work to allow the whole lot to cool as far as possible and not boil the oil in the turbo bearings through heat soak. And also any high performance turbo system also normally has a cooling fan run on set to keep the under bonnet air moving for this reason. I bet the manufacturers never say that as they need to sell the replacement spares!

Ian

mgbv8 · Post by **mgbv8** » Wed Feb 11, 2009 8:39 pm

A mate of mine who races an old BMC A series engine always runs the revs up to about 4000 for a few seconds before shutting it down after idling back through the pits. I must ask why next time I see her!!

stevieturbo · Post by **stevieturbo** » Thu Feb 12, 2009 12:54 am

mgbv8 wrote:A mate of mine who races an old BMC A series engine always runs the revs up to about 4000 for a few seconds before shutting it down after idling back through the pits. I must ask why next time I see her!!

Because they daft ??

Some people do things, just because they think, or are told by old hands, with no real proven reasons for doing so.

Same way some lunatics think its a great idea to give a car a big rev in intial startup. That one almost makes me cringe.

I start the car, drive it. When I want to stop..I stop, and turn it off again. I have never had any problems with this routine, nor have billions of other road users.

ppyvabw · Post by **ppyvabw** » Thu Feb 12, 2009 3:58 am

stevieturbo wrote: Same way some lunatics think its a great idea to give a car a big rev in intial startup. That one almost makes me cringe

Ewwwwwww. My brother does that. (Not because he thinks it's beneficial, just because he's an idiot.)

Straight to 5000 rpm the second it fires. It actually does make me wince.

ChrisJC · Post by **ChrisJC** » Thu Feb 12, 2009 8:27 am

ppyvabw wrote:
stevieturbo wrote: Same way some lunatics think its a great idea to give a car a big rev in intial startup. That one almost makes me cringe
Ewwwwwww. My brother does that. (Not because he thinks it's beneficial, just because he's an idiot.)

Straight to 5000 rpm the second it fires. It actually does make me wince.

My brother used to do that with his MK1 Astra. You could hear metal crashing into metal for a few seconds until the oil got to the top.

New engine was required in short order.....

Chris.

matchmetisse · Post by **matchmetisse** » Thu Feb 12, 2009 12:16 pm

mgbv8 wrote:A mate of mine who races an old BMC A series engine always runs the revs up to about 4000 for a few seconds before shutting it down after idling back through the pits. I must ask why next time I see her!!

I'm suprissed it doesn't carry on running ,always used to on my 1380 mini if the tickover was too high.

topcatcustom · Post by **topcatcustom** » Thu Feb 12, 2009 12:18 pm

matchmetisse wrote:
mgbv8 wrote:A mate of mine who races an old BMC A series engine always runs the revs up to about 4000 for a few seconds before shutting it down after idling back through the pits. I must ask why next time I see her!!
I'm suprissed it doesn't carry on running ,always used to on my 1380 mini if the tickover was too high.

Mine too!

Boosted LS1 · Post by **Boosted LS1** » Thu Feb 12, 2009 7:03 pm

ppyvabw wrote:
stevieturbo wrote: Same way some lunatics think its a great idea to give a car a big rev in intial startup. That one almost makes me cringe
Ewwwwwww. My brother does that. (Not because he thinks it's beneficial, just because he's an idiot.)

Straight to 5000 rpm the second it fires. It actually does make me wince.

I'll give a new engine a burst when it fires for the first time because this beds the rings in. After that it's life as normal.