How slowly can your engine idle stably ( w-o load / rocking ) ?

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TE Chea - 20 Mar 2007 10:26 GMT

I think this minimum idle speed indicates [i] engine's low end
torque [ii] how healthy / efficient an engine is ( @ least during
low rpm ) [iii] how good the petrol is ( lousy petrols give less
torque ).
In this humid air @27-33ºC, my honda F20A
www.autozone.com/servlet/UiBroker?UseCase=RG001&UserAction=beginRepairGuide
originally ( with cheapo 4-1 exhaust*manifold, & carbon core
spark cables ) could idle @ 680 rpm & no lower, but after I [i]
disabled its internal EGR ( worse than useless in cooling
combustion / cylinder head temperature ) [ii] corrected a few (
electrical ) design flaws [iii] replaced * with a 4-2-1 *, & spark
cables with tri-core 0.2 ohm cables [iv] cleaned injectors using
detergent, this F20A ( with just mineral oil w-o fullerene ) can
idle @ 580 rpm ( per tachometer ) using BP ron97 ( has the best
v-f-m in m'sia ; Vpower costs 11+% more ) : mpg is @ an all
time high.
I'm sure engines can idle slower in dry air, none with
carburetors that I've owned can idle this slowly I presume
those with vtec / supercharger, or 1 coil for each s-plug (
distributorless ), can idle slower than a F20A can.

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Mike Romain - 20 Mar 2007 15:27 GMT

Well, I for one like to use my heater and wipers and stereo at idle so I
want my engine running 'at spec' or in my case 650 rpm to keep the
alternator turned on so I don't kill my battery.

I think 'pulling power' at low RPM tells how healthy the engine is. My
carb engine will walk up sand pit walls as low as 400 rpm without stalling.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
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> I think this minimum idle speed indicates [i] engine's low end
> torque [ii] how healthy / efficient an engine is ( @ least during
[quoted text clipped - 16 lines]
> those with vtec / supercharger, or 1 coil for each s-plug (
> distributorless ), can idle slower than a F20A can.

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Steve - 20 Mar 2007 16:20 GMT

I also like my cam lobes to stay pointy rather than rounding off, which
is possible with flat-tappet cams due to collapse of the oil film if the
cam is turning too slowly. Another good reason to stick with specified
idle RPM.

Roller cam engines could safely idle at cranking speed, I suppose. I've
read that the Chrysler 5.7 Hemi factory idle speed is rather low (~5xx
RPM) for efficiency. But I'm sure the alternator is selected to have
sufficient output at that speed, the oiling system still delivers
adequate volume, the water pump circulates enough coolant, etc. etc. etc.

> Well, I for one like to use my heater and wipers and stereo at idle so I
> want my engine running 'at spec' or in my case 650 rpm to keep the
[quoted text clipped - 31 lines]
>> those with vtec / supercharger, or 1 coil for each s-plug (
>> distributorless ), can idle slower than a F20A can.

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Steve W. - 20 Mar 2007 19:44 GMT

Well I have a carbed engine in the shop that idles at about 60 RPM. It's
a 35 HP Fairbanks-Morse. It weighs about twice what that entire Honda
weighs though.....

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Steve W.
Near Cooperstown, New York

"Life should NOT be a journey to the grave with the intention of
arriving safely in an attractive and well preserved body, but rather to
skid in sideways, BBQ in one hand, martini in the other, body
thoroughly used up, totally worn out and screaming: "WOO HOO what a ride!"

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lugnut - 20 Mar 2007 20:48 GMT

>> Well, I for one like to use my heater and wipers and stereo at idle so I
>> want my engine running 'at spec' or in my case 650 rpm to keep the
[quoted text clipped - 35 lines]
>a 35 HP Fairbanks-Morse. It weighs about twice what that entire Honda
>weighs though.....

Yep! And, it is WFO at less than the Honda should idle.

Lugnut

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Steve B. - 21 Mar 2007 00:31 GMT

> I'm sure engines can idle slower in dry air, none with
> carburetors that I've owned can idle this slowly I presume
> those with vtec / supercharger, or 1 coil for each s-plug (
> distributorless ), can idle slower than a F20A can.

You must have owned some carb cars that were in pretty poor shape.
Both of my old girls *can* idle just fine in the low 400s (and on
plain ol' unleaded). I would never leave them there because you don't
get enough oil pressure for comfort and the alternator cuts out.

Last time I cleaned the throttle body on the Cadi ('94 Deville) I
adjusted the manual idle l and it had no trouble idling at 450rpm
either.

Steve B.

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