Prolonged Idle Periods

[AL427SBF]

I've read several recommendations on idling etiquette, and some from very reputable performance motor builders. What has been said is that it's not advisable to let the motor sit and idle for extended periods of time, give it a quick rev once in a while. Interestingly, with that sage advice comes no explanation why, just do it. I'm thinking has to be oil pressure, need to keep the oil circulating for a lot of reasons, particularly on hot days in stop'n go traffic. Don't know about the rest of you, but there are times when I'm not looking for attention with repeated quick revs at a stop, sometimes that's perceived as an invitation for a 1 block blitz to the next red light, no thanks. There are some electric aircraft oil pumps out there that are reliable, small, light weight and give you 50 psi steady state pressure at the flip of a switch. Just thinking that would be an option if oil pressure is the only concern with extended idle periods.

[CHANMADD]

These pushrod engines require a certain amount of oil to be splashed onto the camshaft to lubricate the lifter /cam surface.This is also controlled by the rod side clearances, which ifbto tight will speedbup cam and lifter deteriotion if you idle for too long. Remember when a motor is started new for the first time it is taken directly to about 2500 rpm and kept there so the the cam and lifters can run in without grinding away.......

[AL427SBF]

Thanks CHANMADD, kind of what I thought, exsessive idling = unnecessary oil starved wear & tear. Sounds like an electric oil pump might be the way to go.

[ERA Chas]

No it's not. You don't need 50psi at 800RPM.
If you're in a street situation stopped at lights or traffic, just pick up the throttle to 1200 or so RPM and hold it. That's not a challenge to anyone and you shouldn't worry if it is.
You're also speeding up the water pump a bit which helps with temp control.
You're in a Cobra-don't worry what others think.

[olddog]

Another issue talked about is fuel loading up. Large ports result in low velocity in the intake track at idle. This allows fuel to drop out of suspension and form on the walls. Large droplets drag along and eventually drip into the cylinders where it washes oil off of the cylinder walls, causing excessive wear.

Large cams with a lot of valve over lap exasperate the problem. At idle, the intake vacuum sucks exhaust gasses backward into the intake manifold, reversing the flow for a brief moment. In order to change directions, the velocity must go to zero, allowing fuel droplets to form. In addition to this, air can get momentarily pulsed backwards in the carburetor, resulting in some air going past the jets a second time. So there are small pockets of intake charge with double the fuel.

On extreme engines you will hear them idle, and over time the idle slows and the engine starts burning richer. If you let it idle for an extended time, when you rev it, it will act like starting a flooded engine with a WOT. It will blow black smoke and putt putt until it clears its throat. An engine like this should not be allowed to idle very long.

[olddog]

Originally Posted by AL427SBF

Thanks CHANMADD, kind of what I thought, exsessive idling = unnecessary oil starved wear & tear. Sounds like an electric oil pump might be the way to go.

The FE guys with the solid lifter blocks are generally the ones who sit around and worry about the cam not getting enough oil slung on them from the crank shaft, as no oil is pumped to the lifters. These engines rely 100% on oil getting splashed on the cam. A hydraulic lifter is always dripping some oil onto the cam lobes. A flat tappet lifter has to have a layer of oil between it and the cam lobe or there will be metal to metal wear. A roller lifter does not slide on the lobe as the roller is more like a tire rolling on the ground. Although the roller itself is a bearing that requires lubrication, I would think a roller lifter does not require nearly as much oil as a flat tappet. Certainly not on the cam lobe.

I'm not sure a small block with a hydraulic roller lifter has any risk of not getting enough cam shaft lubrication at an idle.

Pistons rely on splashed oil as well. You never hear of a piston failure from lack of oil during extended idling.

Some of this concern may be for engine designs that you are not using.

[AL427SBF]

Well I'm in the small block hydraulic roller lifter category so probbaly ok "as-is", thanks for the input.

[blykins]

Not necessary with a hydraulic roller. Let it idle where it wants and don't give it a second thought.

If it were a rowdy solid roller, I would just keep the idle at around 1100-1200 and again, not give it a second thought.

[AL427SBF]

Thanks Brent, with that input I won't give it a 2nd thought.

[CHANMADD]

Some of the high end roller lifters, solids and hydraulics have oil bleeds drilled to directly feed the needle rollers in the lifters......