Idle speeds and RPM's

[Pakrat]

OK well, as I mentioned on a different thread, once I finally got my header leak under control I was feeling like I was on a roll and decided to tweak my timing and carb and hook up my tach and stuff like that. Well, I settled on 16 degrees BTDC and ended up leaning out the carb just a tad, my question is what if anything can be found out about if it is running at peak or not by knowing the RPM's now? I mean the car sounds excellent, it has never felt better either. Both idle and acceleration felt great. Here is what the tach had to say for my 3spd manual. Intitial start idle was at 650rpm's and once it hit operating temp it was at around 850rpm's. 2nd gear wound up to about 3800rpm at 60mph once I hit the on ramp and when I hit 80 in 3rd gear it was cruising at about 2700rpm. Does that sound about right or efficient? I have no idea what the engines redline would be, but I always imagined my highway RPM's would be higher than that before the tach and rarely brought it over 70 but it would seem I can go even faster with little or no worry (not that I want to though with drum brakes).

 

[mustang70]

What gears are you running? I have 3:1 in mine and turn 3K at 70 mph. But then I also have a short tire.

 

[Pakrat]

2:79:1 but that is more what I believe is in there still, not what I have actually verified. I figured I'd do that when I get the whole thing on stands for winter storage.

 

[mustangdave]

Your initial start r.p.m.'s is backwards. If you are running a choke, it should idle higher, then settle to a lower r.p.m. Was that a typo or is your engine telling you it's ready for takeoff?

 

[Pakrat]

Nope, the choke is disconnected, my car just runs better without it. Well actually I have noticed little difference when cold, but with it connected the hot starts were never that, well, hot.

Why, is 850 too much? All I have to do is lean the idle out a little more to knock that down don't I? It sure doesn't sound like a plane, it idles very nicely at this range and does not smell rich at all. I know all my newer stock cars idle at more like 500, but there isn't much I can say my old car and my newer cars ever have in common, and let's face it, at least with the Mustang, stock settings are always enimic and geared more towards economy than they are performance.

 

[mustangdave]

650 is great for a stock engine and 850 is great with a small cam; there's nothing wrong with your idle r.p.m., it just struck me as odd that it went up. Now that we know your choke is disconnected, it's all good. Without the choke, the engine is struggking to idle until it warms up and then it smoothes out; I've ran mine that way for years but hope to change that with the new Holley Avenger.

 

[Pakrat]

OK cool, yeah the CAM was upgraded along with the 4V carb intake and headers, the basic improvment package for beginners. You hit the nail on the head too, it is not at 650 for very long, but it does struggle in the begining and you have to tease it with the pedal for a few seconds before it will smooth out and continue to idle instead of choking itself out. It is really weird. When cold the car sparks instantly when you turn the key with or without the choke but needs help to maintian it without where as when hot it takes a few seconds of cranking before it will catch but idles fine instantly wihtout yet if the choke is attached a hot start seems near impossible. Things like this I have learnt to simply accept and not question, I just do what it takes to run happily regardless of if it is kosher or not, like a quirk, we all have them.