# Idle Speed - How Low is Too Low?



## Atarchus (Aug 4, 2020)

I have a 461ci engine with a mild hydraulic roller cam (230 @.050) with Edelbrock EFI. I currently have the idle set at 650rpm, it idles pretty smooth and sounds nice, drives perfect and everything is great. Can I go down to a 600 idle safely? I know lower idle will lower oil pressure, so I was just wondering if there is such thing as too low of an idle?


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## PontiacJim (Dec 29, 2012)

Atarchus said:


> I have a 461ci engine with a mild hydraulic roller cam (230 @.050) with Edelbrock EFI. I currently have the idle set at 650rpm, it idles pretty smooth and sounds nice, drives perfect and everything is great. Can I go down to a 600 idle safely? I know lower idle will lower oil pressure, so I was just wondering if there is such thing as too low of an idle?


Why mess with a good thing? All you can do is try it and see. Too low can cause oil pressure to drop - watch your gauge. Too low can also have the engine stalling out - especially if power brakes and a hard braking situation. Some cams need a higher RPM to make vacuum, so that could be an issue and also become a braking issue with power brakes. Too low could cause insufficient cooling as it may not draw enough air across the radiator.

Just a few things to watch for, but you can certainly give it a try.


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## Atarchus (Aug 4, 2020)

PontiacJim said:


> Why mess with a good thing? All you can do is try it and see. Too low can cause oil pressure to drop - watch your gauge. Too low can also have the engine stalling out - especially if power brakes and a hard braking situation. Some cams need a higher RPM to make vacuum, so that could be an issue and also become a braking issue with power brakes. Too low could cause insufficient cooling as it may not draw enough air across the radiator.
> 
> Just a few things to watch for, but you can certainly give it a try.


I have electric fans, so no worry about cooling and I still have about 13in vacuum at 650rpm, so I don't think I'll have any issues going lower. I might just leave it at 650, I was just curious if there was a certain RPM that was widely seen as the danger line for too low.


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## Lemans guy (Oct 14, 2014)

Factory settings were like 550 and 600, 650 you can look that up. But your motor is not factory, it has a stroked crank and is bored. So your idle would not necessarily be factory either. Maybe one could get it there. I am with PJ if it is already that low and runs good that is nice.

many hot cams require a bit higher idle, but you can always see how low you can go. But Inwould not go lower if it gets rougher, idle speed and smoothness of idle matter as well.

one can go real low and it is chugging and almost stalling but still runs.

How low can you go? Each engine combo is different but not lower than a factory 400 engine with whatever trans you have. Auto trans and manual have different idle settings.


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## Mine'sa66 (Oct 30, 2019)

650 certainly isn't a lot. I'm not sure what's to be gained. In addition to losing oil pressure you're also losing coolant flow, so keep an eye on that. Not just overall overheat issues, but hot spots in heads that might not show up in your temp gauge. I'm of course assuming a mechanical water pump here, but as the rpms get low, pressure can drop off quickly and while there will still be flow, pressure will be lower potentially causing spots. Other minor concern is that your alternator will also start to lose output. Spin that alternator slowly, your fans kick on, voltage drops, amperage increases, you start wearing things out.
Food for thought.


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