468, seams to be starving for fuel top end... - Impala Tech
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post #1 of 5 (permalink) Old 07-22-2019, 07:48 PM Thread Starter
Join Date: Nov 2008
Location: Park River, ND
Posts: 73
468, seams to be starving for fuel top end...

Like I said, motor seams to be starving for fuel at upper room range. Anything over 3,500 rpms it starts to run like crap, missing bucking and such. Mechanical fuel pump the engine builder installed as a new build probably 4-5 years ago. After the switch from automatic to 4spd the problem really is apparent. Do I go with a new performance mechanical pump or electric? What rating electric do I need? How many gph do I need? Help!
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post #2 of 5 (permalink) Old 07-22-2019, 09:41 PM
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First thing before you throw parts at it is to figure out what is wrong with it. It was working before the manual install so it had been working with what you have.

My first guess is a clogged or restrictive fuel line. Need to pull off the line that feeds the carb and measure with a stop watch and a bucket how much fuel you are getting to the carb. You might be amazed at what you see if you use a light colored bucket as black rust flakes magically appear in your gas. These cars are old made of galvanized mild steel and prone to rust due to condensation in the gas tank if you ever parked it not topped off.

Next thing I would check is the fuel filter at the cab inlet, or just replace an in line fuel filter. Since you are border line on running lean be aware that a motor back fires (that pail of open gas). That is why I recommended running another line from the pump to the pail located away from the car.

A stock mechanical fuel pump on a SBC will feed 300 horsepower, on a BBC a mechanical pump can support 450 horse. I don't like mechanical pumps because not only are they limited on fuel delivery they such the heat out of the block and heat up the fuel which also makes you run leaner (in my youth we used to run cool cans just to get rid of the heat, but now they are illegal because they spill water on the track).

Notice there is a difference between a SBC pump and the BBC pump (they both bolt up interchanging with each other at the block face, except ...) they have different shaped and length arms.

Finally you didn't mention the size of your fuel line. All motors over 300 horsepower had a 3/8th inch fuel line, base engines had a 5/16th line. If you have increased your motors power level you have to upgrade the fuel delivery system as well.

By the way the reason most people hate an electric fuel pump is because they are noisey. Be prepared for that if you switch over.

Big Dave
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post #3 of 5 (permalink) Old 07-23-2019, 01:23 PM Thread Starter
Join Date: Nov 2008
Location: Park River, ND
Posts: 73
Dave. The fuel line is 3/8" from the fuel cell which is the rubber or plastic type all the way to the fuel pump and carburetor. I don't believe the switch over to manual has anything other than I probably am running it harder through the gears, more upper rpms than with the turbo 400 which is why I am noticing the problem more.
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post #4 of 5 (permalink) Old 07-23-2019, 01:47 PM
Join Date: Jan 2006
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I agree the manual is allowing the engine to rev faster, but not higher.

I used a half inch solid fuel line to feed my Dominator fed by a 22 gallon fuel cell in the trunk and pushed forward with an Aeromotive A1000 fuel pump strained by BG filters (100 micron before the pump and a 10 micron between the pump and the carb). But I was running a 582 cubic inch BBC.

What are you running, power wise.? You select the pump by the horsepower it has to feed.

Big Dave
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post #5 of 5 (permalink) Old 07-23-2019, 10:28 PM
Join Date: Aug 2008
Location: Miamisburg, Oh.
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Definitely agree on selecting the fuel pump by the power output. I've got no good input on your choice though. Seems that if you're at 600ish or less HP that there should be a mechanical option for you. Certainly the easier road. I personally don't have time to invite more work than needed. heheh

Have you considered the possibility of a coil related issue causing your problem? I mean, I'm assuming you double-checked the entire fuel line to really be 100% certain there's no kink or bad bend, and checked not only the fuel filter, but checked for any copper filter in the carb inlet. (like some have)

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