23 replies to this topic

[Nathan]

During my trip to Goodwood last month I noticed a common practise when it came to warming up engines, constant short bursts of throttle. Why is this done?

What is the ideal/proper procedure to warming up a motor?

[imaginesix]

I would think idle speed until oil pressure comes up, and then bring up the engine speed as much as you are in a rush to get it warm.

But blipping sounds cool.

[Nathan]

I think the backround car was an Auto Union.

The Mercedes guys would start with blips to around 2500 then go up to 3500, I assume once oil temp and pressure reaches a certain level.

[primer]

During my trip to Goodwood last month I noticed a common practise when it came to warming up engines, constant short bursts of throttle. Why is this done?

Were they two stroke motorcycle engines? Some two strokes tend to shut off at idle (due to tune?) thus have to be constantly blipped to keep them running.

What is the ideal/proper procedure to warming up a motor?

For road cars, manufacturers manuals almost always recommend not to idle rather start and drive away slowly and let the car warm itself. BMW handled this nicely in their M3, they had indication lights on tachometer which cautioned the driver to keep the engine RPMs below a certain threshold before things were warmed up nicely. Foreplay before hard action.

[GeorgeTheCar]

I wonder if it is a way to warm up an engine or just a habit leaned when carburetted engines would not run cleanly at low rpm when cold so you would run them at what ever rpm they would run relatively cleanly then drop them back to an idle and repeat and then just passed on from mechanic to mechanic

Edited by GeorgeTheCar, 27 July 2009 - 03:23.

[Jonathan]

What is the ideal/proper procedure to warming up a motor?

Here in New England on a cold winter day, many people will start their cars and just let them idle until the engine becomes warm ( ~ 20 minutes or so) and then hop in and drive off. While it maybe the most comfortable way to get to work in the morning, it certainly isnt the best way for the car to be warmed up.

IMO the best way of getting a normal road car up to temperature is to first start it and let it idle until full oil pressure is reached (15-20 seconds on a normal day.. maybe a minute or so on an especially cold day), and then to drive it gently at low to moderate RPMs (1,000 to say 2,500 RPM) until the the coolant reaches near normal operating temperature. Letting a car idle until it reaches full operating temperature means that it will be running cold for a long period of time when the fuel/air mixture is overly rich, something you generally want to avoid.

Race motors typically are tuned for high RPM power and don't run especially well in the low to mid RPM ranges. Attempting to drive a highly tuned race motor in the 1,000 to 2,500 RPM range is likely to prove something of a challenge. The procedure mentioned here (Gently "blipping" the throttle) makes the engine accelerate and deaccelerate and helps generate heat quickly with out exposing it to load at RPM ranges where it doesn't run very well. As the engine begins to warm up higher and higher RPMs may be used. Finally when the motor is near normal operating range, it can then be driven "gently" by race car standards until full operating temperature is achieved.

IIRC, some pre-1960ies vintage motors often times required special "hot" spark plugs to get the motor up to temperature, and then once full operating temperature was achieved the mechanics would then swap out the "hot" spark plugs, and then quickly replace them with a cooler running plug that would carbon foul at low RPM but would run comfortably for extended periods of time at high RPMs.

[Bill S]

On my race engine, there would be too much oil pressure if I were to run in hard from cold, and I'm nervous about spinning a bearing.
I've seen that happen on a few rally cars, where they've been sitting around for a while waiting for a stage to clear. The guys got into them with not warm-up and a short time later you could hear a conrod or two rattling away.
Also on my racer I often pre-heat the oil with a camping water heater.

[Nathan]

Were they two stroke motorcycle engines?

No. There may have been two strokes that did, but I'm not a bike guy

IIRC, some pre-1960ies vintage motors often times required special "hot" spark plugs to get the motor up to temperature, and then once full operating temperature was achieved the mechanics would then swap out the "hot" spark plugs, and then quickly replace them with a cooler running plug that would carbon foul at low RPM but would run comfortably for extended periods of time at high RPMs.

This explains the spark plug swap on all those Silver Arrows.


Thanks for the great explanations!

[GreenMachine]

The engine builder's instructions for warming my race car are explicit - steady idle of 2500 rpm. Keep revs down until oil reaches 80 degC, when it is good to go. His view is that hard use before the oil is up to temp is the biggest single cause of engine wear/failure.

[gordmac]

With a competition engine I would run it at a constant speed rather than blip the throttle. Every time you blip it the accelerator pumps in the carbs will squirt fuel in, I don't think the rich mixture would be good for the engine. Maybe not such an issue with injection?
I have heard that the old all alloy Lotus engine (Sunbeam rally car) could jump the cam timing if blipped when cold as the engine hadn't expanded enough to tension the cam belt.
Never mind the sixties engines needing plug changes, we used to have to do that with an evo 4 rally car.

[ferruccio]

Most race engines these days require cooling sytem to be pre-heated by an external heater before starting the engine from cold

[Paul Ranson]

Hypotheses... If a race engine will hold a 'fast idle' it's because the ignition is very ********, so after a while the exhausts melt. The heat is intended to be in the oil and water, so cycling between idle and higher rpm does a better job of warming up. The engine does more work accelerating itself than holding a speed, so that warms it faster.

Or not.

Paul

[carlt]

If they were starting/ warming up classic race cars they prob had weber carbs and race cams .
they won't run at all on start up unless you 'blip' the throttle

[gruntguru]

With a competition engine I would run it at a constant speed rather than blip the throttle. Every time you blip it the accelerator pumps in the carbs will squirt fuel in, I don't think the rich mixture would be good for the engine. Maybe not such an issue with injection?

Agree entirely. Steady speed is the go. Aim for a balance of lowest speed with least enrichment. This balance will change as the engine warms up.

[FrankB]

Here in New England on a cold winter day, many people will start their cars and just let them idle until the engine becomes warm ( ~ 20 minutes or so) and then hop in and drive off. While it maybe the most comfortable way to get to work in the morning, it certainly isnt the best way for the car to be warmed up.

OT - Here in old England the criminal element of our wonderful society regularly go out "frosting" on winter mornings. Cruise around the suburban streets looking for cars sitting on drives with the engine running, trying to de-frost the windscreen and warm up the cabin while the owner is back inside the house having a last cup of coffee. By the time the coffee is finished your car is long gone - and I shouldn't think the insurance companies are particularly sympathetic.

Edited by FrankB, 10 August 2009 - 13:03.

[mariner]

I think the "blip" explanation for carbs is probably the origins of this - anyway blipping sounded cool!

In terms of what revs to use, if a pushrod engine has a steep cam profile and non roller tappets( lifters) then cam scuffing is a possble risk ar low revs, espeically with a dry sump. This is because the cam relies on oil splash from the sump for lubrication. As a dry sump scavenges the oil out there is not enough oil mist in the sump until the crank gets whirling it at high RPM.

So the advice I have always received is to keep the revs up above 2,000 to avoid scuffing but not so high as to raise the oil pessure above about 100-120psi ( 8 bar) or you risk blowing an oil line at start up. Juggling at thaose rules with a big carb means blipping it.

BTW somewhere on the nostalia forum ( I think) is a wonderful explanation on starting a turbo offy- that is REALLY complex

[Wilyman]

A Volvo rally car I was involved with in the late '70's had extensive head work done. The engineers advice was a slow warm up, their concern was that the bronze valve guides could loosen because of different metal temp. variation.

Wily TNF*118

[tristancliffe]

Idling is bad for engines, particularly cams. At half engine speed, the cam lobes wear very quickly at low speed. At higher speeds (i.e. driving gently) then tribology predicts (and practice proves) less wear. You are also less likely to be running rich at idle (with carbs), so less washing of oil from your bores.

In short - idling kills engines. Far far better to get in and drive, and just put warmer clothes on if it's cold outside.

On a race car it's often impractical to drive them before going out, so a fast idle reduces camshaft wear and reduces bore washing (amongst other things). Blipping is added partly because it apparently sounds cool (but is usually only done by people who don't know what they're doing - if you ever hear people trying to cure a misfire in the paddock and checking by revving it up to 500rpm+ you can be sure that a) the misfire will still be there and b) the engine won't last long or won't produce good power) and partly because engines also prefer to run at different speeds periodically.

Ever heard the old running in advice of not staying at constant revs for too long? Same reason! (although this advice often tells you to avoid full throttle, when actually you want to get enough combustion pressure to bed the rings in).

Rant over

[RacingMonk]

I seem to remember Keith Duckworth being asked the best way to warm up an engine and he said something to the effect of bring up the revs to the point where you hear most internal mechanical noise then hold it there until the noise dies away.

[gruntguru]

I seem to remember Keith Duckworth being asked the best way to warm up an engine and he said something to the effect of bring up the revs to the point where you hear most internal mechanical noise then hold it there until the noise dies away.

Good for diagnosis too - if the noise suddenly gets louder, you know somethings broken.

[Greg Locock]

I seem to remember Keith Duckworth being asked the best way to warm up an engine and he said something to the effect of bring up the revs to the point where you hear most internal mechanical noise then hold it there until the noise dies away.

I think you may be misinterpreting a quiet joke.

[McGuire]

I think you may be misinterpreting a quiet joke.

Exactly. That should indeed produce the maximum engine temperature in the minimum elapsed time. Duckworth had a flair for the sardonic.

[gruntguru]

Exactly. That should indeed produce the maximum engine temperature in the minimum elapsed time. Duckworth had a flair for the sardonic.

Hmm, I think a brick on the throttle pedal (then walk briskly away) would be even quicker.

[Fat Boy]

A legitimate reason to blip the throttle is that that the (mechanical) water pump on a race engine generally turns very slow. It's meant to work at high rpm, not idling. So, if you just let the engine idle all day, it may not move any water which could cause ugly localized hot bits. By blipping the throttle here and there and getting the revs up for short periods of time, you can move the water around and keep things happy.