Best idle speed

Tom's36coupe

Tom's36coupe

Well-known member
Just wondering what the best idle speed would be for the Flathead. I have been running about 800 but lately tried about 500 and it sounds pretty cool! Is that too low, almost feels like its going to stall....If it is higher around 800 or so is that starting to get into the advance on the distributor?
 
also, around where i live there are a lot of stop lights and i take my truck out of
gear and my foot off the clutch. the low idle speed makes it easy to slide back in gear. the ford service Manuel says to set idle speed so the car will go about 3 mph in high gear on level ground
 
If the engine is tuned right and running good these engines will idle real slow. You want to adjust the air mixture valves real good at a slow idle. As long as they don't stall when you snap your foot of the gas pedal you can't get it to low. People are amazed when they hear them, or can just about hear them running. G.M.
 
Stock 8BA 475 rpm. if ford-o-matic 425 rpm. if you have a built up motor with a cam its where ever it idles best for you.
 
I have been adjusting the idle screws some and its amazing how much it impacts the rpms. Had them turned out 1 full then tried about 1/2 a turn and the rpms picked up a bit. With 1 turn out on both carbs it seemed to be rich at the exhaust pipes.
 
A lot of people like to show-off on how slow their engine will run. That is a big mistake, if you have much traffic driving to do.
At slow idle, your water pumps do not pump water, you don't exchange as much air in the engine compartment and your oil pressure drops.
On the highway, it doesn't make any difference, of course.
MIKE :)
 
Mike got it right. Contrary to what has been said here it is entirely possible to idle too slow. Not only is proper coolant flow suppressed but also proper oiling of the internal parts. The camshaft/lifters and cylinder walls/pistons must have oil cast onto them from the rotating crank assembly. This will not happen if RPM is too low. Ford introduced squirt hole rods which were used during the last few years of production to improve the slow speed oiling of internal components.
 
jdl said:
Stock 8BA 475 rpm. if ford-o-matic 425 rpm. if you have a built up motor with a cam its where ever it idles best for you.
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I should have stated that those idle settings are from the 49-51 Ford shop manual. I have mine set at 500-550 range seems o.k.for my driving habits.
 
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