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What causes stinky idle with performance cam?
#1271730
07/22/12 01:16 AM
07/22/12 01:16 AM
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Joined: Jul 2008
Posts: 259
Khemi, Stygia
Mebsuta
OP
enthusiast
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OP
enthusiast
Joined: Jul 2008
Posts: 259
Khemi, Stygia
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What is the biggest culprit of stinky idle with a performance cam? You know, where it smells like a big lawn mower and gets all over you if you walk behind it. Is it overlap, late exhaust valve closing, or something else?
I don't care too much but some gurlz won't ride in a stinky car.
Last edited by Mebsuta; 07/22/12 01:19 AM.
68 Roadrunner. 383 4-spd. Beat up.
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Re: What causes stinky idle with performance cam?
[Re: Mebsuta]
#1271731
07/22/12 02:02 AM
07/22/12 02:02 AM
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Joined: Feb 2003
Posts: 1,665
Milwaukee, WI
Prince_Valiant
top fuel
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top fuel
Joined: Feb 2003
Posts: 1,665
Milwaukee, WI
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Overlap causing reversion.
The reversion is basically spent exhaust doesn't fully exit, and a good fresh charge of fuel and exhaust then don't fully enter, and leads to a poor combustion (which also might be occurring from low-dynamic compression due to very low intake velocity from the big cam). Add it all together and there you have it...poor idle...
1979 Dodge Lil' Red Express - 360 rwhp, 13.2 @ 103mph
1968 Coronet: 318, 2.76, 15.2 @ 92mph! (SOLD)
1976 Valiant: 360, 3.90, 12.90 @ 106 (SOLD)
1989 Shelby CSX #500/500
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Re: What causes stinky idle with performance cam?
[Re: Prince_Valiant]
#1271732
07/22/12 04:01 AM
07/22/12 04:01 AM
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Joined: Jul 2011
Posts: 817
Eugene, Oregon
Secret Chimp
super stock
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super stock
Joined: Jul 2011
Posts: 817
Eugene, Oregon
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Supposedly a four hole or split spacer will help cure this from a standpoint of the exhaust interfering with carb signaling, unless you're running a single-plane intake or a dual-plane with the divider cut down.
1967 Dodge Coronet Deluxe station wagon
1.03" T-bars, QA1 arms/rods, Cordoba/GM Metric/Volare brake & knuckle, XHDs, Hellwig rear sway, 318 Magnum w/ air gap, 727, 3.23s
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Re: What causes stinky idle with performance cam?
[Re: RSNOMO]
#1271740
07/22/12 01:45 PM
07/22/12 01:45 PM
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Joined: Jul 2005
Posts: 1,954
Blairsden, CA
Triggerfish
top fuel
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top fuel
Joined: Jul 2005
Posts: 1,954
Blairsden, CA
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Quote:
'Put some C-12 race fuel in it and when you find a girl that loves the smell..... Marry her.'
There's some righteous advice...
I agree & get a lot of thumbs up from female truck lovers, but until I swap the huge cam in my 383 mag for the Lunati Truck Avenger cam I ordered, I'm in the same boat. Not only fuel smell & wet tail pipes, but my low stall verter, tall tires & gears makes for lousy low end performance & poor fuel economy. Installing a 1" 4 hole spacer on the Weiand dual plane & 600 eddy carb + bumping initial to 20 improved low end manners a little, but still not acceptable for street performance.
Thought of Rhodes lifters to tame the overlap, but heard they're not that predictable. Think a cam swap is your best solution to not only fix the smell issue, but better performance & fuel economy.
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Re: What causes stinky idle with performance cam?
[Re: jbc426]
#1271744
07/23/12 06:53 AM
07/23/12 06:53 AM
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Joined: Jul 2008
Posts: 259
Khemi, Stygia
Mebsuta
OP
enthusiast
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OP
enthusiast
Joined: Jul 2008
Posts: 259
Khemi, Stygia
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Right now I use the 383 HP cam in a 383 Roadrunner. It has 46 degrees of overlap. Ignition timing is 8 degrees BTDC, by the book. Don't know what the total is. I use ported vacuum advance. Manifold vacuum at idle is 16 inches at 700-750pm. Runs good, just smells like a big Briggs and Stratton. Always has.
Thing is, I might try something with a tighter LSA and close the intake valve earlier. That gives you more overlap and bumpty hot-for-teacher idle, which gurlz like, but if it's going to be more stinky, they don't like that. Gurlz want it all don't they? Luv them anyway.
68 Roadrunner. 383 4-spd. Beat up.
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Re: What causes stinky idle with performance cam?
[Re: RobX4406]
#1271747
07/23/12 08:19 AM
07/23/12 08:19 AM
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Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
Challenger 1
Too Many Posts
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Too Many Posts
Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
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Quote:
People get pretty clean idles with 250+ at .050 cams and others can't get a clean idle with a cam with 20-30 degrees less duration and overlap.
Maybe it's got more to do with the tune up than the camshaft. The time it using total method crowd are usually pretty good at providing a stinky idle most of the time, unless they get lucky.
JMO
Put a good tune in her and she won't stink.
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Re: What causes stinky idle with performance cam?
[Re: ahy]
#1271748
07/23/12 08:27 AM
07/23/12 08:27 AM
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Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
Challenger 1
Too Many Posts
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Too Many Posts
Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
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Quote:
Agree its high overlap (long duration + tight lobe seperation) that is the main factor. I suspect a single plane manifold makes it worse also.
Tuning can help clear it up... at least partly. Adequate initial advance plus the leanest AF that will hold a steady idle. Mine likes 20 degrees initial advance and around 14.5 air/fuel. Getting those two dialed in helped both vacuum and "fumes".
I use a single plane manifold and my car don't stink at idle. I run 22 degrees intial, I don't know why guys are afriad to run plenty of intial timing.  
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Re: What causes stinky idle with performance cam?
[Re: Challenger 1]
#1271749
07/23/12 09:32 AM
07/23/12 09:32 AM
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Joined: Nov 2004
Posts: 7,274
s.w.fl
bonefish
master
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master
Joined: Nov 2004
Posts: 7,274
s.w.fl
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Quote:
Quote:
People get pretty clean idles with 250+ at .050 cams and others can't get a clean idle with a cam with 20-30 degrees less duration and overlap.
Maybe it's got more to do with the tune up than the camshaft. The time it using total method crowd are usually pretty good at providing a stinky idle most of the time, unless they get lucky.
JMO
Put a good tune in her and she won't stink.
mine was so bad i couldnt even sit at a lite, it would gag people for a country block.i couldnt even tune the car unless i had it facin down wind on a breezy day and i aint jokin.timming and carb fixed it.im runnin a fairly radical street cam.
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