I agree that you may want to upgrade the pump itself. However, if the engine was able to pull 5500 with a 28p prop, then only able to pull 5000 with a 26p prop, you had more going on, than simply a insufficient fuel pump size. I think you may be on to something, as far as the pickup being clogged, a fuel line that collapsed internally, or some junk in the carb. Junk in the carb though, wont show a loss of fuel pressure, where as a clogged screen, filter, line, etc, will.

What I would do, is try to rig up a mechanical gauge, to where someone can see it while you run, temporarily. Forget those electric pieces of crap. Ideally, if you have 6.5-7psi at idle, you dont want to see it drop to 3-4psi at wot. You wanna see it stay around 6 or more at speed. Even most of the mechanical gauges arent very accurate as far as they go. You can take 1 gauge, install it, and see 7psi at idle. Remove it and install another one, and see 8psi at idle. But what you wanna watch is for the pressure drop at high load/speed. If it drops more than 1-2psi say from 3000-5000, you prob have a supply issue.

Your typical holley needle and seat cant take 9psi without being pushed open. The CV product pumps are nice, but, they are not gonna help if the pickup is clogged, lines to small, etc. Also, make sure the tank vent isnt clogged with spider webs.

I have a mechanical gauge on the motor, cell phone and duct tape problem solved!

I wouldn't try to bargain shop on fuel delivery for high hp applications. When I upgraded, I switched to an electric pump, used the existing pickup as a return by bending the pickup tube and removing the screen. Installed a new larger bulkhead fitting in the tank for -10 with a new tube and large in tank strainer. Is grenading a motor worth the $500 you may save?

Found a pump with larger ins and outs off a 600sc that my bud switched to electric. It should support this thing...problem now is the water separator has small ins and outs.

Its always something with these things, good luck

On the bright side it is a 170 gph pump

Sorry to sidetrack - but why would he do that ?

def get a high flow water/fuel filter.... 3/8 line is way undersized... I would say 600HP max with that.... I built my 509 and guess its around 575HP and it does OK with a stock pump and larger lines. I also installed a wide band air/fuel ratio gauge to monitor everything in real time and it is really the way to go to dial in your carb. If you are leaning out and I bet you are, you are running the risk of frying your nice, new motor..... I am running aluminum heads and high compression so I have to run 93 octane from the pump and I am always afraid of the alcohol in the gas creating crud in my fuel system.....
I would also get an AFR gauge, I look at mine all the time. the only thing is you need is to weld an exhaust bung for the O2 sensor. I use a plate with mine as I have the 496 style dry joint exhaust.
I would say going with electric is a good idea. I am going to install an electric setup as a backup just in case my mech pump craps out......

wanted to make sure it had sufficient fuel and he is anal as fuk

Don't tell'm, but my question remains the same..maybe even more so since so anal.

Oh well. Others can learn from this. If you can stay mechanical : ie, you have carb(s) vs EFI, stay mechanical.

My Dirty Floored Shop Opinion. . LOL.