Comp 268 cam idle quality or lack of........Carb tuning
#58405
05/13/08 11:24 PM
05/13/08 11:24 PM
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Posts: 4,848 Memphis
HemiRick
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I have a '75 Low compression 440 w/ this cam Cam Style: Hydraulic flat tappet Basic Operating RPM Range: 1,200-5,200 Intake Duration at 050 inch Lift: 218 Exhaust Duration at 050 inch Lift: 218 Duration at 050 inch Lift: 218 int./218 exh. Advertised Intake Duration: 268 Advertised Exhaust Duration: 268 Advertised Duration: 268 int./268 exh. Intake Valve Lift with Factory Rocker Arm Ratio: 0.454 in. Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.454 in. Valve Lift with Factory Rocker Arm Ratio: 0.454 int./0.454 exh. lift Lobe Separation (degrees): 110
It runs great except for idling in gear....I can't get an idle set that's acceptable. I.E. the RPM drop is too large when put in gear. I've tried several carbs over the years and they all have this basic issue....Currently it has a Carter comp series 750.... What can I try to get this cars idle quality better? Thanks
Take care, Rick 68 Coronet R/T 440 & 68 Charger 528 Hemi,and 5 Challengers! 6 cyl, 318, 360, 383, 451
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Re: Comp 268 cam idle quality or lack of........Carb tuning
[Re: HemiRick]
#58406
05/13/08 11:39 PM
05/13/08 11:39 PM
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Joined: Feb 2003
Posts: 4,204 Fort Worth, TX
Clair_Davis
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What's your initial spark advance? The more, the merrier, if your distributor has a curve that will tolerate that much once you're on the road. That usually means a custom curved distributor.
My old Dart's 440 was also low-compression, and I was running a MP 284/484 beast, with a TIGHT 11" converter. Yeah, not a great combo. Idle vacuum in gear was about 8", in neutral was about 11". Unfortunately, I was a po' collige kid and couldn't ever afford to get my distributor curved - and didn't know how to do it myself. So, 12* was about all I could manage and still drive the car at highway speeds. If I could have gotten 18* it would have been a lot happier.
Clair
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Re: Comp 268 cam idle quality or lack of........Carb tuning
[Re: HemiRick]
#58407
05/13/08 11:40 PM
05/13/08 11:40 PM
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Anonymous
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Anonymous
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try alot more initial timing (no idea where yours it at).. mabey 15+deg. also try to fatten up the idle mixtures to the highest vacuum reading.
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Re: Comp 268 cam idle quality or lack of........Carb tu
#58408
05/13/08 11:44 PM
05/13/08 11:44 PM
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Posts: 4,848 Memphis
HemiRick
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Yea it has a sick amount of initial advance....I'm thinking about changing the cam...to something smaller but the cheap summit cams didn't appear to be much smaller....It has the classic problem of the idle speed is so high (in neutral it has to be this high so as to not stall in gear)that the idle mixture screws dont seem to do much....( in gear the idle quality is so horrible that the engine barely stays running)
Last edited by HemiRick; 05/13/08 11:49 PM.
Take care, Rick 68 Coronet R/T 440 & 68 Charger 528 Hemi,and 5 Challengers! 6 cyl, 318, 360, 383, 451
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Re: Comp 268 cam idle quality or lack of........Carb tu
[Re: HemiRick]
#58410
05/13/08 11:53 PM
05/13/08 11:53 PM
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Anonymous
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Anonymous
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you can tune that out. try to fatten up the idle mixture. what kinda vacuum at idle and in drive?
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Re: Comp 268 cam idle quality or lack of........Carb tu
#58411
05/14/08 12:00 AM
05/14/08 12:00 AM
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Joined: Mar 2003
Posts: 4,848 Memphis
HemiRick
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I've tried restricting the idle air bleeds with no success, the vacuum #'s are like 12" in gear and 18 out of....If I can get a cheap small cam/lifters I'd switch in a minute....Anyone wanna trade? Factory HP for a Comp 268? I have the matching lifters in order.....
Take care, Rick 68 Coronet R/T 440 & 68 Charger 528 Hemi,and 5 Challengers! 6 cyl, 318, 360, 383, 451
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Re: Comp 268 cam idle quality or lack of........Carb tu
[Re: rdrmod6]
#58413
05/14/08 12:14 AM
05/14/08 12:14 AM
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HemiRick
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No I've never tried anything but Edlebrock's/Carters and a Thermoquad on this motor. I have no doubt a new $5/400 carb might fix it, as I have a Speed Demon 850 on a similar 451 I own and was able to tune it. But I just want this car to run nice so I can sell it. BTW it's a 64 Polara vert so it just needs a nice cruiser motor. I just need to find a deal on a stock type cam....
Take care, Rick 68 Coronet R/T 440 & 68 Charger 528 Hemi,and 5 Challengers! 6 cyl, 318, 360, 383, 451
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Re: Comp 268 cam idle quality or lack of........Carb tu
[Re: HemiRick]
#58415
05/14/08 06:06 AM
05/14/08 06:06 AM
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Joined: Feb 2005
Posts: 4,333 Prospect, PA
BSB67
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Rick, if the vacuum goes from 18 to 12, that does not sound like the cam. What kind of rpm drop do you get going from neutral to in-gear? I did not understand your comment about the initial timing. One thing to look for with your timing: be sure that the mechanical advance is not partially coming-in when idling in neutral. If you have some mechanical advance in when in neutral, you will lose some or all of it when you put it in gear, causing a large difference in neutral to in-gear idle quality. I have not run that cam but have run others that, on paper, are larger than that one and had more than 12" vacuum in gear.
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Re: Comp 268 cam idle quality or lack of........Carb tu
[Re: ThermoQuad]
#58417
05/14/08 06:59 AM
05/14/08 06:59 AM
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Joined: Feb 2003
Posts: 12,675 Columbia, CT
moper
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What is your idle speed? You should have no trouble getting a cam with 218°@.050 to idle with 7:1 compression. What distributor/advance curve?
Well, art is art, isn't it? Still, on the other hand, water is water! And east is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does. Now, uh... Now you tell me what you know.
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Re: Comp 268 cam idle quality or lack of........Carb tu
[Re: Nick Mineau]
#58423
05/14/08 11:01 AM
05/14/08 11:01 AM
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HemiRick
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I know how to set the idle mixture thanks Nick....I'm more prone to go with the too tight torque converter theory, as the symptoms really agree. The tranny is a stock BB push button with an unknown converter. The cars slams into gear and jumps from the higher unloaded idle RPM and then barely lopes along in gear. I'll get some actual numbers on idle speeds and vacuum later today. I agree this cam doesn't seem this big and should be able to work....But I haven't to make it so in 10 years of messin with this. Yes this car has ran this way for a long time.
Take care, Rick 68 Coronet R/T 440 & 68 Charger 528 Hemi,and 5 Challengers! 6 cyl, 318, 360, 383, 451
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