What's the ideal RPM range for idling in Neutral?

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Duster Fan

Duster Fan

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My '70 Duster idles at 1,000 to 1,200 RPM in neutral. When I put it in gear, it drops down to 800-900 RPM. Is this ok, or do I need to do some more tweaking on the carb?
 
Forgot to mention, I've got an Eldelbrock Air-Gap intake, with a Holley 750 CFM double pump carb, with a proform main body.
 
I hate idle speeds over 1000 and in a lot of carbs having it that high means you're no longer just using the idle circuits because the blades are open too far. I try to keep mine in the 850-950 range in nuetral and the "normal" rpm drop is only maybe 100rpm with a perforamnce convertor.
However, some very fast rate flat tappet cams will need a higher idle speed in order to gaurantee the cam gets oiled enough.
 
moper said:
I hate idle speeds over 1000 and in a lot of carbs having it that high means you're no longer just using the idle circuits because the blades are open too far. I try to keep mine in the 850-950 range in nuetral and the "normal" rpm drop is only maybe 100rpm with a perforamnce convertor.
However, some very fast rate flat tappet cams will need a higher idle speed in order to gaurantee the cam gets oiled enough.
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What do you consider to be enough idle oil pressure? When I changed from 20-50 to 10-30 my warm engine idle oil pressure dropped to 20 PSI.

My 416 idles at 700-800 in neutral when the engine is warm (purple 508 hyd flat tappet cam).
 
Thats about what mine idles at. MP 484/ 242 cam. Air gap intake and a Holley 750 dp. I can't get it much better than that.
I like the lumpty lump of the whole thing.:D
 
briankaplan said:
Thats about what mine idles at. MP 484/ 242 cam. Air gap intake and a Holley 750 dp. I can't get it much better than that.
I like the lumpty lump of the whole thing.:D
Click to expand...

Oh yeah, I like it as well. Before I had my valves adjusted, its idle in neutral and gear RPMs were both in the 900-800 range. The mechanic decided to screw around with the carb. afterwords and now I've got the 1,200-1,000 RPM idle in neutral. The idle in gear hasn't changed.
 
It's going to want to idle around 1K RPM.

How much initial timing will determine where it idles and how much drop occurs. My guess, it will need at least 20* initial timing. Last 360 I helped with had a 244 at .050 and ended up with 24*.
 
What size engine?
The MM lobes are big... but not too big. Depending on the compression and stroke I'd think it could be idled down a bit even at 108°.

Air - If you have oil pressure ont ehg age at idle, the lower end is fine. 10psi is more than enough at idle assuming the clearances are good. But the cam is not oiled by the oil system. It's only oiled by the splash off the crank. So if the crank isnt spinning fast, and the volume is too low coming off it, the lifter bases can be starved and with a big spring pressure flat tappet, that's not too hard to have happen.
 
I think it's a 318... you get it to idle under 1K with that size cam, I'd be surprised unless you lock out the distributor.
 
crackedback said:
I think it's a 318... you get it to idle under 1K with that size cam, I'd be surprised unless you lock out the distributor.
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You're correct. It's a custom built 318. Basically it is a 340, but with a 318 block. It generates about 425 HP as well, not bad for a daily driver, $20k plus, has been put into her so far.
 
moper said:
What size engine?
The MM lobes are big... but not too big. Depending on the compression and stroke I'd think it could be idled down a bit even at 108°.

Air - If you have oil pressure ont ehg age at idle, the lower end is fine. 10psi is more than enough at idle assuming the clearances are good. But the cam is not oiled by the oil system. It's only oiled by the splash off the crank. So if the crank isnt spinning fast, and the volume is too low coming off it, the lifter bases can be starved and with a big spring pressure flat tappet, that's not too hard to have happen.
Click to expand...

Yes I do, about 50 at idle, and about 75 registering on the gauge going down the road.
 
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