Re: Holley DP idle tuning
[Re: Azzkikrcuda]
#469057
09/15/09 02:13 PM
09/15/09 02:13 PM
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Joined: Jan 2003
Posts: 9,982
Ansonia, CT
CJK440
master
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master
Joined: Jan 2003
Posts: 9,982
Ansonia, CT
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Sounds like your primary butterflies are open too far. I bet you see vacuum at the ported vac tap at idle too, a good indicator you are open too far.
A PV that opens at idle shouldn't affect idle mixture much if at all.
2017 Contusion Blue Challenger T/A 392 M6 "BLKNBLU"
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Re: Holley DP idle tuning
[Re: Azzkikrcuda]
#469064
09/15/09 07:56 PM
09/15/09 07:56 PM
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Anonymous
Unregistered
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Anonymous
Unregistered
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You say initial timing is fine, how do you know? If you advance the timing right now, at idle, will the RPM go up????? If so, you don't have enough initial timing.......
Power valve HAS NOTHING TO DO WITH idle mixture, unless it's blown........
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Re: Holley DP idle tuning
#469065
09/15/09 08:23 PM
09/15/09 08:23 PM
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Joined: Jan 2003
Posts: 10,766
Central Valley, CA.
Quicksilver440
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 10,766
Central Valley, CA.
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Quote:
You say initial timing is fine, how do you know? If you advance the timing right now, at idle, will the RPM go up????? If so, you don't have enough initial timing.......
I've never heard this before...can you explain this?
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Re: Holley DP idle tuning
[Re: CJK440]
#469067
09/15/09 08:41 PM
09/15/09 08:41 PM
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Joined: Apr 2005
Posts: 12,271
Overpriced Housing Central
RobX4406
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I Live Here
Joined: Apr 2005
Posts: 12,271
Overpriced Housing Central
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Quote:
Quote:
Quote:
You say initial timing is fine, how do you know? If you advance the timing right now, at idle, will the RPM go up????? If so, you don't have enough initial timing.......
I've never heard this before...can you explain this?
Yes please. I didn't want to get off on a tangent when somebody mentioned ideal initial timing but this begs some more info.
Maybe it maximizes combustion efficiency.
Same reason you hook up a vacuum gauge to set intial, keeping rpm constant and feeding in lead to max vacuum, then back out 1" by retarding.
Most stuff I see, especially carb issues at idle, are rooted in the ignition most of the time. The majority in this group are the total timing at xxxx rpm folks. Act like initial doesn't matter when using mech adv distributors.
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Re: Holley DP idle tuning
[Re: CJK440]
#469068
09/15/09 08:43 PM
09/15/09 08:43 PM
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Joined: Nov 2007
Posts: 21,833
Kirkland, Washington
Pacnorthcuda
Too Many Posts
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Too Many Posts
Joined: Nov 2007
Posts: 21,833
Kirkland, Washington
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Quote:
Quote:
Quote:
You say initial timing is fine, how do you know? If you advance the timing right now, at idle, will the RPM go up????? If so, you don't have enough initial timing.......
I've never heard this before...can you explain this?
Yes please. I didn't want to get off on a tangent when somebody mentioned ideal initial timing but this begs some more info.
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Re: Holley DP idle tuning
[Re: Pacnorthcuda]
#469069
09/15/09 08:48 PM
09/15/09 08:48 PM
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Joined: Jan 2003
Posts: 9,982
Ansonia, CT
CJK440
master
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master
Joined: Jan 2003
Posts: 9,982
Ansonia, CT
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This new challenger I bought had a rough idle and ~5in/hg vac. Initial was single digits so I arbitrarily cut some mechanical out and ended up with about ~18 initial. Vacuum jumped to almost 10 in/hg and idle smoothed a bunch. Also was much more responsive when the throttle is zinged. Fired with a quick hit of the key too.
I do realize the benefits, just didn't know of a scientific way to find ideal initial for your specific combo. I suppose adjusting base timing for max vac at a given RPM makes sense.
2017 Contusion Blue Challenger T/A 392 M6 "BLKNBLU"
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Re: Holley DP idle tuning
[Re: Quicksilver440]
#469070
09/16/09 12:08 AM
09/16/09 12:08 AM
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Anonymous
Unregistered
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Anonymous
Unregistered
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Quote:
Quote:
You say initial timing is fine, how do you know? If you advance the timing right now, at idle, will the RPM go up????? If so, you don't have enough initial timing.......
I've never heard this before...can you explain this?
Simple........It's EXACTLY like adjusting timing for max power at the drag strip or on the dyno........You keep advancing the timing until the motor stops making power or the MPH stops going up...........only at idle, it's all about advancing the timing until it stops gaining RPM......
If you fire the plug sooner, and the RPM goes up, why does it do that? You didn't add air or fuel.......All you're doing is firing the plug sooner.....if that makes the RPM go up, you burned more air and fuel, there was a bigger bang in the cylinder, and the RPM went up.......so there's less raw fuel running out the exhaust pipe.........You've just affected your O2 numbers........
What I do is pick an RPM that the motor sounds good idling at......say 900RPM.........Then keep advancing the timing and resetting the idle RPM back to 900RPM until you hit a point of diminishing returns.......You can use a vacuum gauge too........Then, as long as it starts fine when heat soaked, that's what your motor wants........If it does start hard, back the timing up 2 degrees at at time until it does start good.......Then curve the dizzy to have that much initial along with the total it wants.....  
RobX4406 hit the nail right on the head......
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Re: Holley DP idle tuning
#469071
09/16/09 02:33 AM
09/16/09 02:33 AM
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Joined: Jan 2003
Posts: 10,766
Central Valley, CA.
Quicksilver440
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 10,766
Central Valley, CA.
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Quote:
Quote:
Quote:
You say initial timing is fine, how do you know? If you advance the timing right now, at idle, will the RPM go up????? If so, you don't have enough initial timing.......
I've never heard this before...can you explain this?
Simple........It's EXACTLY like adjusting timing for max power at the drag strip or on the dyno........You keep advancing the timing until the motor stops making power or the MPH stops going up...........only at idle, it's all about advancing the timing until it stops gaining RPM......
If you fire the plug sooner, and the RPM goes up, why does it do that? You didn't add air or fuel.......All you're doing is firing the plug sooner.....if that makes the RPM go up, you burned more air and fuel, there was a bigger bang in the cylinder, and the RPM went up.......so there's less raw fuel running out the exhaust pipe.........You've just affected your O2 numbers........
What I do is pick an RPM that the motor sounds good idling at......say 900RPM.........Then keep advancing the timing and resetting the idle RPM back to 900RPM until you hit a point of diminishing returns.......You can use a vacuum gauge too........Then, as long as it starts fine when heat soaked, that's what your motor wants........If it does start hard, back the timing up 2 degrees at at time until it does start good.......Then curve the dizzy to have that much initial along with the total it wants.....
RobX4406 hit the nail right on the head......
Thanks Big Squeze...I've never heard that before. I'll give it a try. I usually run 18 initial and 35-36 total anyways....I'll see what it does doing it your way.
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Re: Holley DP idle tuning
#469072
09/16/09 02:41 AM
09/16/09 02:41 AM
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Joined: Aug 2003
Posts: 8,716
Baltimore/Denver
64Post
master
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master
Joined: Aug 2003
Posts: 8,716
Baltimore/Denver
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Quote:
Quote:
Quote:
You say initial timing is fine, how do you know? If you advance the timing right now, at idle, will the RPM go up????? If so, you don't have enough initial timing.......
I've never heard this before...can you explain this?
Simple........It's EXACTLY like adjusting timing for max power at the drag strip or on the dyno........You keep advancing the timing until the motor stops making power or the MPH stops going up...........only at idle, it's all about advancing the timing until it stops gaining RPM......
If you fire the plug sooner, and the RPM goes up, why does it do that? You didn't add air or fuel.......All you're doing is firing the plug sooner.....if that makes the RPM go up, you burned more air and fuel, there was a bigger bang in the cylinder, and the RPM went up.......so there's less raw fuel running out the exhaust pipe.........You've just affected your O2 numbers........
What I do is pick an RPM that the motor sounds good idling at......say 900RPM.........Then keep advancing the timing and resetting the idle RPM back to 900RPM until you hit a point of diminishing returns.......You can use a vacuum gauge too........Then, as long as it starts fine when heat soaked, that's what your motor wants........If it does start hard, back the timing up 2 degrees at at time until it does start good.......Then curve the dizzy to have that much initial along with the total it wants.....
RobX4406 hit the nail right on the head......
Pretty much the same way I did mine. I ended up with 24º initial, 12º mechanical, all in at 2700 rpm.
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Re: Holley DP idle tuning
[Re: 64Post]
#469073
09/21/09 01:54 PM
09/21/09 01:54 PM
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Joined: Nov 2006
Posts: 2,255
IL
furious70
top fuel
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top fuel
Joined: Nov 2006
Posts: 2,255
IL
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very interesting and simple way to think about it. I'm going to test it out with my FAST efi system, very easy to change the timing and watch the IAC, O2, and injector duty cycle change!
70 Sport Fury
68 Charger
69 Coronet
72 RR
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Might be time to do some bleed work. Or you may try cracking the secondaries open a bit, small bit and backing down the primary idle screws first though.
Is this a late model DP with stock four corner idle circuits? If not try opening the rear buuterflays about .020 or less and try that 
