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Old 02-01-2004, 11:19 PM
western star's Avatar
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Changed to Airgap...problem

I have a 350 with excellent compression. Running a 268 Comp cam and headers. Was using Edelbrock Performer with 600 Edelbrock carb (new) This motor ran sweet with good jump. I changed to a Edelbrock Airgap intake and I have lost my bottom end power. It runs very strong about 2500 RPM and up but at low rpm's it seems to fall on it's face for a couple of seconds and then responds. Everthing is fine, choke, timing, fuel etc. Being that the Airgap puts the carb further away or up higher could this be the problem with stock compression. I just though I would get some input before changing the manifold back. Remember everything worked beautifully before changing intakes.

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Old 02-01-2004, 11:47 PM
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Changing an intake manifold won't have any effect on the engines compression. I'd check for a vacuum leak first. Make sure that the vacuum advance hose is tight on both ends and the unused vacuum ports are capped good. Check all of the manifold/carb baseplate bolts and make sure they are all tight. Get some carb or brake parts cleaner and spray it on the intake manifold and baseplate gaskets while the engine is running. If it changes speed or seems to make any momentary change in exhaust note then that's your problem.
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Old 02-01-2004, 11:51 PM
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I am sure if you look on the advertised power band of both intakes you would see that it is the reason.
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Old 02-02-2004, 12:39 AM
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yuppers, a performer or weiand stealth would have been a better choice. That intake is not a very good compliment to your cam either. Sorry guy, you'll have to swap it out again.

K
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Old 02-02-2004, 12:44 AM
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Just for my own curiosity, you said you went from a EB performer to an EB Air Gap performer manifold. Is that correct? Not an RPM Air Gap? Sorry, I'm not trying to be a **********, but just curious. Theoretically there should'nt be any real noticeable loss in bottom end drive-ability providing it's getting warm enough to provide continuous fuel atomization during cold ambient temperatures. Mind you, the manifold should eventually soak in enough heat to overcome this whilst driving. The only glaring variable that I can think of at this stage would be maybe that the ignition timing's not set at it's original setting once the distributor was reinstalled. Did you disconnect the vacuum line from the dizzie when you adjusted the ignition timing? Anyhow keep us posted. Rob
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Old 02-02-2004, 08:16 AM
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western star, what is your definition of falling on its face. Does it feel like a mixture or timing problem where the engine bogs and then comes on or does it just pull less.
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Old 02-02-2004, 10:00 AM
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I agree with those that stated it is the difference in the manifold design/RPM range. The regular Performer manifold is designed for "stock type" applications and has a RPM range of idle to 5,500RPM. The performer "RPM" (air gap or not doesn't matter) has a RPM range of ~ 1,500 - 6,500RPM. I agree it is not a good match for your cam as well.

I am sure you can "tune out" the problem (the bog), but don't expect to have the same low RPM performance out of the RPM manifold in your application, it is designed to operate at a higher RPM and in a "higher" performance application.

You can either put in a little larger cam and a stall converter, or you might want to switch back to the regular Performer.

Keep in mind when you change one thing it usually effects something else. This is why the right "combination" of parts is critical if you want to get the most out of the car/engine.

Royce
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Old 02-02-2004, 05:46 PM
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It is an EB RPM Aigap. The timming is right. It is a stumble or a slight bog and lower rpms. A slight bog then comes on. I am going to try a few of your pointers for sure. This is my son's truck and I didn't drive it until today. The hesitation is there but I think with some tweeking I can correct this. Once you have the engine up to about 2000 it has great snap to it. I also found something else he did. He does not have the electric choke wired in and he has the choke flap secured wide open. This would explain it falling on it's face when cold. We'll get that hooked up and play with some other settings and let you know. Thanks all for your help.
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Old 02-02-2004, 07:44 PM
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with that manifold you need to make sure your carb primers are doing a good job it might help to put larger squirters on it i think it will end your bog try it
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Old 02-02-2004, 11:26 PM
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That carb is a little small to begin with. Edelbrock carbs aren't as easy to tune to your engine as a Holley would be. Put that together with a stock distributor curve and there is your bog.

If you want that manifold to perform better re-curve your distributor. Go with 16o to 18o of distributor advance and have it come in by 2,500 RPMs. Your distributor curve is just as important as your fuel curve, (a point that somehow is overlooked by most hotrodders).

If you tune everything correctly and make sure there is no vacuum leak or other not so obvious problems, that manifold will make more power all around than your original one did. It all depends on the engine/drive train combo as to how a manifold will work. With the right timing, fuel, gearing, and stall, even a single plane manifold could perform as good or better than a dual plane in some cases.
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Old 02-03-2004, 08:22 AM
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The air gap is going to require some fine tuning. Experiment with the boost shot size. The stock booster is mostly likely too small for the air gap. Also set the timing to 36 deg total mechanical advance and do some experimenting there as well. Hook up the vacuum advance to the manifold port vacuum source. Edelbrock carbs are easily to tune. You can change step up springs, metering rods and jets as well as the booster. Just do one change at a time so you can measure the difference. I would start with the timing then pay around with the booster. As a starting point with the booster though, make sure the linkage rod is set to the hole closest to the top of the carb. This will give you the long fuel shot at a slightly slower rate than the other two settings.

Last edited by Steve karch; 02-04-2004 at 06:25 AM.
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Old 02-03-2004, 10:35 AM
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an edelbrock 600 is definately not too small for a very mild 350 small block such as this. You're just going to hurt your low end further by decreasing the low end air velocity with a larger carb.

Just my .02

K
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Old 02-03-2004, 11:29 AM
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It is quite possible you stumble is caused by the fact that the air cap intake has to exhaust cross over in it where you old intake the performer did. With out the cross over especially in colder temperatures a stumble when you first hit the gas is very common. It can probably be tuned out satisfactorily though.
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Old 02-03-2004, 01:33 PM
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BOG =not enough pump shot. carb height is now farther away=less signal
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Old 02-03-2004, 06:28 PM
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Great info and all points recorded. Thank you very much.
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