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Old 09-17-2012, 02:51 PM
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big cam idle blues

OK, just tired of breathing pig rich fumes at idle (or staying on the pedal while staging), both suck. Timing locked at 38, SBC 355, 283/296 @ .050, 108 lobe center installed at 105 centerline, what's the secret? I see other SBC cars with pretty big cams and they somehow manage it. I've tried different things, drilling butterflies (works with smaller cams), using a pcv port on the carb for even more idle air, IAB's, IFR's, etc..

Before I get slammed for the big cam I just want to say that I like the sound of 9,000 rpm's, but it will never idle right with a small cubed SBC.

Please let me know what's the trick or give me some examples of long duration cams that still idle on their own. (automatic cars of course)

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Old 09-17-2012, 03:48 PM
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It'll never idle well. you can get it to idle better though with a properly matched exhaust- it'll help cut down on reversion some but it'll always be there at idle with that huge cam. reversion is what's killing you.

a well developed mpfi system can also help.
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Old 09-17-2012, 05:00 PM
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what heads and valves?injection might be the only way.auto or stick?what size carb are you using?
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Old 09-17-2012, 05:07 PM
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This motor will idle great at 1,400 rpms on the stand but once you put the converter and vacuum pump on it the idle will go away. It will idle ok at 50+ timing and this is one thing I haven't tried yet, I suppose I could keep one of the retard stages from my 4 stage retard box (1 stage retard during the run and none at idle) but that leaves it at the mercy of the box. No power valves, currently has a 950 HP on it with a 4150 to 4500 adapter sitting on a dart 4500 intake, when I used the pcv port I put a multi turn flow valve on the hose end but it would still only help slightly with valve fully open. Headers are stepped 2" to 2 1/8" to 2 1/4" with 3 1/2" collecter. Also I'm running a Hughes 4000 stall with a 150 shot of happy stuff to get off the line. It seems that no matter which adjustment you make to get a decent idle (IFR,IAB,4-corner), it still is rich one way or the other. Right now, the transfer slots are good and you have to keep it running with constant pedal action. no room for exhaust (tube chassis Vega)

Thanks for the replies and keep it comming, I'm not busy and you need the post counts,
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Old 09-17-2012, 05:37 PM
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here is the latest adition to the 355, a set of Crower stainless shaft rockers with needle bearing tips, you'd show them off too if you paid over $1,400 for a set of rocker arms.
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Old 09-17-2012, 05:42 PM
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with those big tube headers,big cam and big intake,I bet the signal is quite weak. 1,400 might be where it idles.Can you switch/block the vacuum pump from **** pit?
did you build those headers?
maybe use an idle stop solenoid that engages when car is in gear
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Old 09-17-2012, 05:50 PM
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what is the inside of an airplane called? the part where the pilot sits?lol,sorry for setting off the language blocker
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Old 09-17-2012, 06:14 PM
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I reckon 1400rpm idle is GOOD with a cam that long..
I ran a sig erson cam back in the 70's with 274/286 @50 in a 383ci idle at 1500 -lovely with 5000stall. Would want nothin less.
4000 is toooo small ..... Listen to EVERYTHING that F'BIRD-88 says!

Duke
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Old 09-17-2012, 06:15 PM
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correct on all counts, guilty as charged, this a different 355 but still using the same cam. I put it in, then I complain about it, it's a vicious cycle, but man does it scream! It's definitely not a nitrous cam and to make things worse, the tire is a 33-10.5w with a 4:10 gear and Jimmy Arabie glide. I got this roller (tube chassis, strut front, 20 point cage, aluminum center chunk, glide etc.) very cheap so I threw this motor in it. This cam has never been able to idle without choking you, even with a loose converter. It's a fresh build and pulls fine, just won't idle. I know that before putting in the multi stage retard, I bumped it up some and when I checked it it was at 55 deg and idled fine. Obviously I backed it down to 39 deg. and that's where she sits now.
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Old 09-17-2012, 06:34 PM
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Don't intend to leave it the way it is now, just seeing what it would do with this set-up, my main question was about idle. I had to save for a while for the rockers but they are worth every penny, no more girdles!. The engine was on the test stand for initial start-up. Will a tunnel ram give me better idle? forget about the car for now, the motor probably won't be in there for long.
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Old 09-17-2012, 06:51 PM
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will do, I'll try the timing thing and let you know, you guys type alot faster than I do, as for the cam, I'm a "dapper dan man", I mean a "Herbert cam man". Changing the cam isn't that big of a pain because of the Horizontal bar lifters and the shaft rockers.
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Old 09-17-2012, 07:10 PM
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the headers are huge for a 355,,,
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Old 09-17-2012, 07:12 PM
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Heads are ported Brodix Track1's, and yes, hair treatments of different names are pretty much the same too, I just like the Herbert billet rollers.

Thanks for the replies,
gotta go,
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Old 09-17-2012, 07:18 PM
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I'm not worried about the car right now as I will either change rear gears, converter etc. or sell the roller. This chassis has been in the 7's and I don't have near enough motor or money to give it the heart transplant that it needs. What this motor needs is my 4 speed and vertical inline shifter I used on my 66 chevelle in the 70's
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Old 09-17-2012, 07:25 PM
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we use speeds and 6 speeds now.have fun with it,w/e you do.
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