225 Slant needs a good idle. what rpms are you spinning?

-
gdizzle

gdizzle

Well-Known Member
Joined
May 25, 2015
Messages
954
Reaction score
56
Location
los angeles
I think I asked this once before, but I want to be as specific as possible here.
66 dart, slant, sedan, super six conversion , carter bbd, HEI conversion, 904 auto.

ok, so after engine is completely warmed up and driving, if I come to a stop light, remain in drive with foot on brake, my idle is about 580. Feels sorta low, but what do you guys think?

what do you guys get while in gear, at a stop, engine fully warmed.
 
as long as the headlights aren't dimming, and the oil pressure is sufficient, and there are no other adverse issues from a low idle speed, I see no reason to jack up the idle to some unnecessary spec.
 
Idle speed specs are just as "unnecessary" (i.e., necessary) as every other spec on the car. 580 is too slow. Shoot for 700 in Park with the high beams on. If you have A/C, shoot for 800 in Park with the high beams on and the A/C off.
 
I agree that you should speed that thing up a little bit, but, there is something really soothing about a smooth, low idling Slant.
I have the one in my 62 Savoy so low, that you can watch each individual fan blade swing by.
 
maybe there's no drag on the engine, because there is little frictional losses on his engine. I'm just saying, if the engine WANTS to idle lower than some arbitrary number, say 700, does it really NEED to be sped up to this arbitrary speed? I imagine the idle speed specs are an average recommended speed, taking into account fresh oem engines. Maybe his engine is an outlier, and doesn't require 700rpm idle speed.
 
rustycowll69 said:
maybe there's no drag on the engine, because there is little frictional losses on his engine. I'm just saying, if the engine WANTS to idle lower than some arbitrary number, say 700, does it really NEED to be sped up to this arbitrary speed? I imagine the idle speed specs are an average recommended speed, taking into account fresh oem engines. Maybe his engine is an outlier, and doesn't require 700rpm idle speed.
Click to expand...
I agree!
When I was a kid, just learning about working on cars back in the middle 70s, I remember very distinctly that the mark of a good tune up was how low you could get it to idle and still be perfectly smooth.
Oldsmobile Nailheads were the best. You could get those things down so low you could just about grab a fan blade and stop it.
 
rustycowll69 said:
maybe there's no drag on the engine, because there is little frictional losses on his engine.
Click to expand...

There are significant frictional losses on his (and every other) engine.

if the engine WANTS to idle lower than some arbitrary number, say 700, does it really NEED to be sped up to this arbitrary speed?
Click to expand...

The engine doesn't "want" anything -- not a Cherry Coca Cola Slurpee, not a cigarette, not a pot of gold, not a pot of chicken soup, and not to idle at 580 rpm. It's idling at 580 rpm because the speed is not properly adjusted. The correct speed isn't arbitrary; it's what happens when all the relevant adjustments (idle mixture, ignition timing, idle speed screw) are set correctly, and the result is that everything works optimally in terms of how the car starts, runs, and drives. That's not arbitrary (or random, or magic), it's just how it works. The carburetor's idle transfer port and vacuum spark advance port are in very specific locations relative to the throttle plates, for example, and everything's calibrated based on the throttle plates being where they're supposed to be. You've got some lattitude, of course; it's not like the car won't run (or will run like crap) if you don't hit the spec dead on target, but 580 is far enough below where it should be that there are going to be problems—some of which are already mentioned (line voltage droop).

I imagine the idle speed specs are an average recommended speed
Click to expand...

It doesn't work the way you imagine.
 
What the book says and what your vehicle likes are 2 different things. I can dial mine down to below 300 in park and it will still run until I put it in gear, dies, to slow to run. The only real benefit is that you'll be saving gas and that's about it, if your oil and volts are happy at that idle, then so be it.
 
Well
Dan
is right
For proper low-speed operation the Transfer-port sync is very important. And this sync operates quite far up the rpm band in neutral. I'll wager you can hit 2500 on the sync, and maybe 3000, even.
The factory made it easy for us to hit the sync point by specifying valve lash,the idle-rpm,the idle-timing, the rate of advance, and the power-timing is built-in. If the engine is fresh, or in good working condition, and factory stock,then you will not improve on their specs. Sure you can dick the timing around or dick the sync around, but in the long run, and for hitting the most targets,you won't make it any better.
But if you like 580 in gear, and like others have said,if it doesn't hesitate on throttle tip-in, and the oil-pressure is ok,then enjoy it for what it is.
Now, if you modify that engine, then you get to re-engineer all the tuning requirements, to hit as many targets as you can,starting with the T-port sync. When you are done you can print up a new spec sheet, for following owners.

Having said that, I remember this one engine I had, that made this wonderful thoop,thoop,thoop,thoop,thoop sound at a way-too-low idle rpm. That was a 69 340 with a complete 318 top end on it including the cam, but with fenderwell headers, in a 65 V100 wagon, with 2" straight pipes out the back, and little Thrush shorties.
Thoop,thoop,thoop,thoop,thoop,thoop,thoop,thoop,thoop,thoop,thoop,thoop.
I bet it was like 500rpm in gear,lol.Maybe less
 
Last edited:
500-700 idle ? Shoot I can't keep mine idle under 1000. Are you all setting your timing at that low of rpm ? Geez . Wonder why i can't keep mine at idle at less than 1000-1200 ish best .
 
Johnny71dusty said:
500-700 idle ? Shoot I can't keep mine idle under 1000. Are you all setting your timing at that low of rpm ? Geez . Wonder why i can't keep mine at idle at less than 1000-1200 ish best .
Click to expand...

May have a vaccum leak. What's your vacuum like at idle in Park?

My Slant has always idled about 750 in park and 550ish in gear. The only time it's ever idled in your range is when I've had a vacuum leak.
 
Spray some carb cleaner around the base of the car & such, keeping it away from the intake barrel.. If rpm rises u have a leak somewhere..... vacuum or gasket

Also check carb bolts to manifoeld for tightness
 
Thru are
Blainethemono said:
Spray some carb cleaner around the base of the car & such, keeping it away from the intake barrel.. If rpm rises u have a leak somewhere..... vacuum or gasket

Also check carb bolts to manifoeld for tightness

I pulled manifolds off 3 times . I got the good gasket Everyone said to get . It's got all them tight to the higher end of the spec . Using carb cleaner I see no signs of leaks at manifold side
Click to expand...
 
my twin webers set up can idle as low as 550 in drive , usually have it around 650
takes of like bat out a hell ether setting , like the sound of it when it slow
 
67belevdere/225 said:
my twin webers set up can idle as low as 550 in drive , usually have it around 650
takes of like bat out a hell ether setting , like the sound of it when it slow
Click to expand...
Yes I don't know I can't keep mine running even ideling at 1000-1200 . Stalls and is so very inconsistent . Can't find a vacuum leak . All hoses are off and porttw plugged . Get no rpm Increase spraying carb cleaning around intake
 
67belevdere/225 said:
my twin webers set up can idle as low as 550 in drive , usually have it around 650
takes of like bat out a hell ether setting , like the sound of it when it slow
Click to expand...

Webers are an entirely different world. I bet that 6 just sings with them. How about some pictures?
 
Johnny71dusty said:
Yes I don't know I can't keep mine running even ideling at 1000-1200 . Stalls and is so very inconsistent . Can't find a vacuum leak . All hoses are off and porttw plugged . Get no rpm Increase spraying carb cleaning around intake
Click to expand...

One issue Ive always had with tuning carbs is getting the idle screw back to "base" where the engine is running off the idle circuit, & not above it. Back the idle adjuster screw all the way until it is not touching its stop. Screw it in until it just touches the stop, then 1 more full turn. Start engine, what does it do?

In my love/hate journey, I found out the Accelerator pumps felt was drier then Betty Whites Muffin, & it would always stumble off idle due to this. Hence a higher idle rpm to bypass that stumble. Tried a new one, got better, but still wasnt what I wanted.

This is also a great time to ask our group to lock down how many turns the idle mixture screw is to be turned out from fully seated? 1 turn, 1 1/2? 2? whatever works?

Personally, I finally gave up on my POS carb & bought a newly remanufactured one. End of carb headaches
 
Last edited:
Idle mixture screw setting for best running is gonna vary a bit engine to engine. You can tweak out a carb and get it running absolutely great on an engine then drop that carb on another engine and there's a good chance you will have to tweak it again to run it's best on the 2nd engine.
I usually set them around 1-1/4 to 1-1/2 turns from lightly seated to start off with. And from there? "Whatever works" for that particular engine
 
volaredon said:
Idle mixture screw setting for best running is gonna vary a bit engine to engine. You can tweak out a carb and get it running absolutely great on an engine then drop that carb on another engine and there's a good chance you will have to tweak it again to run it's best on the 2nd engine.
I usually set them around 1-1/4 to 1-1/2 turns from lightly seated to start off with. And from there? "Whatever works" for that particular engine
Click to expand...
Yea I get you but not my issue . My ideal screw is all the way out . It's still field very rough at 1000-1200 . Even with distributor all the way retarded . Yes already pulled thr distributor and too dead center and Tried move plugs over one spot to see about getting to closer . It's acting like classic vacuum leak but can't find one anywhere . The motor prior to head swap ran very low rpms , never once stalled , had way more power in pedal . The new head has 100 thousands off and should have slightly better compression and more power. But it's now a total dog and idle high . Stalls , has no power even at full throttle . I'm about to set the car on fire
 
You must log in or register to reply here.
-

Back
Top