Fireguyfire
Active Member
What do you guys and gals recommend to set engine idle at on a 440 engine, and secondly how are you going about setting engine idle speed if you don’t have a tachometer?
Engine idle rpm
- Thread starter Fireguyfire
- Start date
Depending upon several things, the OEM idle speed can vary between 550rpm - 750rpm. Usually, about 600 rpm in "P" works pretty well. IF you have no tach and some time, here's a way I prototyped back in the early 1970s.
First, with the engine fully warmed-up to operating temperature (air conditioner operating long enough to cool things down with the lh door open, IF equipped). Apply the parking brake fully and firmly! Then, with your lh foot on the applied foot brake pedal, shift the trans into "D" and see how it feels, the engagement should be smoooth, yet firm (after all, it's a TF). Then, slightly blip the throttle to see if it responds to that input. THEN (the reason the parking brake is firmly applied), carefully take your foot off of the foot brake and go to the rear of the car and put your hand near the end of the tail pipe. You will be checking for the smoothness of the gas flow AND the smell of the gas flow (to detect hydrocarbons which if they are tooo much, means a too-rich mixture). Hydrocarbon smell should be minimal.
If the gas flow is smooth, yet the "D" engagement was a bit harsh, turn the idle speed down 1/4 turn. Then go back and check the gas flow for smoothness. When the idle speed is too slow, you'll be able to feel each individual pulse out of the pipe. When you get to that point, then increase the in-gear idle speed to just where the gas flow becomes smooth again. Or maybe another 1/8th turn of the idle speed screw from there, for good measure. Remember, this is IN GEAR idle speed, for which the FSM generally has no specs.
Then, when you get there "in gear", put the shift lever in "P" and you can tweak the idle mixture screws a bit to ensure they are at "lean best idle". You can use the engine cooling fan noise for a speed reference. Blip the throttle lightly to check for good response, then let the engine settle back down to its hot base idle. Apply the foot brake, holding it, as you put the trans in "D" to check for smooth engagement, then recheck the pulses at the tail pipe outlet. If still good, then put the trans in "P" and check to see that the engine stops quickly when you turn the ign key OFF. Then check for a good hot restart action, which probably should not need any throttle pedal action. If everything acts well, you're done.
THEN, when you get to where you can hook the engine up to a dwell tach, you can further fine-tune the idle mixture and adjust the hot base idle speed after those tweaks.
NOW, this works well with a single exhaust car, less so with a dual exhaust car, as to the exhaust pulses and such. Although you probably could stuff a shop rag in the side the heat rise is on, provided of course, that the passage in the intake manifold is still operational.
End result is that you have the base idle speed slow enough that the car idles smoooth in gear, or as smooth as the cam will let it. But also fast enough that it will not overheat in gear, with the a/c on, in traffic.
My adventures of using a vac gauge to set the idle mixture and such were not good, back in the later 1960s after I bought a vac gauge for such things. It was not accurate enough for what I wanted, unfortunately. When I got a quality dwell tach, I was much happier. Just my experiences.
All of this might take 15 minutes or so AND REQUIRES a working parking brake! Proceed at your own risk! But once you get the reference points down, then verified later with a dwell tach, you'll know how to set things up again, later, to duplicate the results. AND you can check things with or without the air cleaner installed. AND you can compare the results with the factory specs, to see how close you might be to them, for a general reference.
Take care,
CBODY67
First, with the engine fully warmed-up to operating temperature (air conditioner operating long enough to cool things down with the lh door open, IF equipped). Apply the parking brake fully and firmly! Then, with your lh foot on the applied foot brake pedal, shift the trans into "D" and see how it feels, the engagement should be smoooth, yet firm (after all, it's a TF). Then, slightly blip the throttle to see if it responds to that input. THEN (the reason the parking brake is firmly applied), carefully take your foot off of the foot brake and go to the rear of the car and put your hand near the end of the tail pipe. You will be checking for the smoothness of the gas flow AND the smell of the gas flow (to detect hydrocarbons which if they are tooo much, means a too-rich mixture). Hydrocarbon smell should be minimal.
If the gas flow is smooth, yet the "D" engagement was a bit harsh, turn the idle speed down 1/4 turn. Then go back and check the gas flow for smoothness. When the idle speed is too slow, you'll be able to feel each individual pulse out of the pipe. When you get to that point, then increase the in-gear idle speed to just where the gas flow becomes smooth again. Or maybe another 1/8th turn of the idle speed screw from there, for good measure. Remember, this is IN GEAR idle speed, for which the FSM generally has no specs.
Then, when you get there "in gear", put the shift lever in "P" and you can tweak the idle mixture screws a bit to ensure they are at "lean best idle". You can use the engine cooling fan noise for a speed reference. Blip the throttle lightly to check for good response, then let the engine settle back down to its hot base idle. Apply the foot brake, holding it, as you put the trans in "D" to check for smooth engagement, then recheck the pulses at the tail pipe outlet. If still good, then put the trans in "P" and check to see that the engine stops quickly when you turn the ign key OFF. Then check for a good hot restart action, which probably should not need any throttle pedal action. If everything acts well, you're done.
THEN, when you get to where you can hook the engine up to a dwell tach, you can further fine-tune the idle mixture and adjust the hot base idle speed after those tweaks.
NOW, this works well with a single exhaust car, less so with a dual exhaust car, as to the exhaust pulses and such. Although you probably could stuff a shop rag in the side the heat rise is on, provided of course, that the passage in the intake manifold is still operational.
End result is that you have the base idle speed slow enough that the car idles smoooth in gear, or as smooth as the cam will let it. But also fast enough that it will not overheat in gear, with the a/c on, in traffic.
My adventures of using a vac gauge to set the idle mixture and such were not good, back in the later 1960s after I bought a vac gauge for such things. It was not accurate enough for what I wanted, unfortunately. When I got a quality dwell tach, I was much happier. Just my experiences.
All of this might take 15 minutes or so AND REQUIRES a working parking brake! Proceed at your own risk! But once you get the reference points down, then verified later with a dwell tach, you'll know how to set things up again, later, to duplicate the results. AND you can check things with or without the air cleaner installed. AND you can compare the results with the factory specs, to see how close you might be to them, for a general reference.
Take care,
CBODY67
Fireguyfire
Active Member
Great advice, thanks!
I use a Dwell Meter that reads RPM.
Have the meter hooked up, get the car up to operating temperature, (Here's where I work backwards), with foot on brake, put the car in DRIVE, Turn on A/C if equipped, set an RPM that's smooth for when you will be sitting at a Red Light. The Neutral Idle RPM will be where ever it ends up at.
My 505ci idles at 1000rpm in Neutral, 800rpm in DRIVE with foot on brake and 730rpm when A/C is turned on. Any lower and it chugs and can stall at Red Lights.
Have the meter hooked up, get the car up to operating temperature, (Here's where I work backwards), with foot on brake, put the car in DRIVE, Turn on A/C if equipped, set an RPM that's smooth for when you will be sitting at a Red Light. The Neutral Idle RPM will be where ever it ends up at.
My 505ci idles at 1000rpm in Neutral, 800rpm in DRIVE with foot on brake and 730rpm when A/C is turned on. Any lower and it chugs and can stall at Red Lights.
Ripinator
Old Man with a Hat
Bite the bullet and buy a dwell / tach meter. This tool is as fundamental to you as a screw driver. . . especially if your engine uses points ignition. These meters are all over E-Pay, and our member @halifaxhops has several for sale too.
Thanks Rip. I have them for all skill levels and prices are all over the place 40 and up. I would recomend a starter set, Tach/dwell, timing light and a vacuum guage to have on hand.
My best investment was a dial back timing light with rpm readout. Found a 10-15% off coupon on either ORiellys or Autozone, purchased it on their website for pick up a went and got it. I believe with taxes it was under $70. Using this was how I found my mechanical advance was off (advance was kicking in at idle speed making it impossible to set low idle) It was either 550 rpm or 900 rpm. Also used it to dial in my vacuum advance to the correct curve per the factory specifications.
For dwell tach multi meter multi use tool with thermometer probe. Harbor freight has one for around $40. Instructions are iffy but not too bad. LCD Automotive Multimeter with Tachometer Kit
Mine came with a temperature probe(I used gloves and just held it on the radiator and thermostat housing.). With all the tools I own I still haven’t sprung for a cheap laser thermometer.
Mine came with a temperature probe(I used gloves and just held it on the radiator and thermostat housing.). With all the tools I own I still haven’t sprung for a cheap laser thermometer.
A digital dial back light is great. The analouge ones are usually off so I run from them.
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