loss of fuel pressure at WOT
 

I am running a Holley black electric pump. all the lines are 8an braided steel all the way to the tank. the tank pick up line also has been increased. The way the line runs is as follows

Tank pick up ,20" to a check valve just before the stock merc fuel water separator. from there 6" of line to the pump. then 12 " of line to the Holley regulator. then 28" of line to the carb. The fuel rail on the carb is one of those chrome ones that I am going to replace soon for safety reasons. ( they don't belong on boats) The pressure sensor is right on the fuel rail . The carb is a modified 850 Holley punched out to a 920 cfm. The motor is a 454 with a inter cooled 177 blower.

I am running 8 psi of pressure. but at WTO (5400 RPM) it drop to 6.5 PSI.

How bad is this on a super charged engine????

Am I loosing any HP from this???

How do I correct this if I need to ????

6 psi is actually fine, but if you plan to run at 6 psi, you need to regulate it to 6 psi all the time and reset your float at 6 psi.

My guess, though, is that you should run the pump before the water separator. It is easier to push than to pull.

I'd also move the regulator as close to the carb rail as possible.

Whatever pressure you end up using, the fuel system should be capable of holding that pressure from idle to WOT.

The check valve is a restriction issue, but is recommended on a boat cause it keeps the tank from self siphoning into the bilge if a line breaks..

its fine and no h.p. drop ///change to push and use a good regulator like a mallory or barry grant not a holley !! Mc above is right :D :D

FIRST OFF, THE SIZE OF YOUR LINE IS FINE BUT CAN BE RESTRICTED BY THE CHECK BALL IF I.D IS VERY SMALL. SECONDLY INSPECT PICK UP FOR MINISCULE CONTAMINANTS WICH CAN CAUSE YOUR PROBLEM. YOU ALSO MUST NOT CHANGE THE ORDER OF THINGS, STRAW, WATER SEP FILTER, PUMP, REGULATOR. ALSO THE FUEL PUMP MUST BE MOUNTED AS CLOSE TO TANKI HEIGHT AS POSSIBLE, FOR AS IT IS HARD TO PULL VERSES PUSH, ADD TO THAT PULL UP FIRST THAN PULL BACK, AND YOUR EFFORTS INCREASE BILL FOLD.

Hey Paul,

Man it sucks to hear you are having some issues!! Have you thought about a bad regulator or pressure sensor giving a false reading? Did you make any changes since last yr.? Low fuel pressure may be creating a lean condition. Could this be relative to your valve problem?

You have some very knowledgeable people responding, but I am a little confused about 6.5 lbs of pressure at WOT. On a supercharged motor the prussure should increase with boost. I would think you should be up around 13 at WOT.

Also my carbs are 750s on my procharged motors. Could your be a little too much?

I am no expert, but maybe someone can correct my points and shed somemore light. I'll talk to you during the week.

If you are using an electric sender. Double check it with a mechanical gage.

pure eneregy you can make a motor blown or N/A increase fuel pressure at speed but its better just to set it right an leave it also 13lbs would blow the needles off the seat ,bad !!!!6 or 7 pounds is all you need ;) ;)

Bobby, I didn't mean to imply setting at 13 lbs at idle. Maybe I am missing something? On a supercharged motor, the fuel pressure should be boost referenced, right? If that is correct, then if he is @ 8 lbs. at idle, then he should be @ 13 lbs. @ WOT with 5 lbs of boost, 1 lb fuel pressure increase per 1 lb of boost increase. I give this info based on my Procharged 502s.

If I am wrong please let me know. Thanks

Two different type of carb setups, One is blow thru ( procharger) where the fuel pressure has to increase as boost increases. Since the carb in a blow thru system is totally contained in a box as the air pressure(boost) goes up so must the fuel pressure. Say in your procharger setup if you are running 7 lbs of boost & carb is set for 6 psi at idle once your boost got to 6 lbs the carb would not get any fuel, thus the reason for your boost reference fuel regulator. You start with 6 & as your boost goes up so does your fuel pressure. The carb would still only be seing the 6 lbs of pressure.

Other steup is suck thru. This is used with a whipple or roots blower. The carbs sit above the blower & the fuel/air is sucked thru. With this setup your fuel pressure will not need to change since the carb is not pressuried.

Got it, thanks!