I am running into sort of the same problem. I don't have blowers, but I built 2 550 hp engines and was planning on running 2- #8 lines back to the tank. The tank was plumbed for #6. When I pulled the fittings, there is a tube screwed into the bottom. The aluminum tube looks like it might be bigger than #6. Can I just change the top fittings to #8? Or would combining the 2 bungs into 1 and splitting at the fuel separator to go to the twins work out for me?

I think you might be over reacting. My 3/8" lines support NA 750HP+ NA BBC twins with CV mechancial pumps. At WOT, the fuel pressure never drops below 6.5 lbs.

I have enlarged aluminum bungs with a greased up drill bit and a greased up tablespoon thru the sending unit hole catching the filings! Some tanks have the big plastic "cover " that is like 3.5x5" that is held on by several screws that one is easy to work on. Ive had custom tubes drilled out and threaded to fit inside the #8 elbow which screws into the tank or sender cover. I know it can be done. The thing is if your boat is really fast I dont think you can really read the guage. Motors are very expensive and if you fry it youll fix it anyway just to make sure and eliminate the potential problems on the new motor! I have 1 V8 and 24 pistons (16 are no good) the other ones are shot due to a lean condition. Either way you will be smarter.:D

What HP do you expect? Figure .5 lbs fuel per hour per HP. You will likely see that these lines can handle more HP than you will be making. To confirm your calculations, run a fuel pressure gauge at the carb(s) you will then always know if you have a fuel delivery issue.
If you can hold over 5 lbs pressure at WOT why go thru the hassel of re-rigging the fuel system?

[QUOTE=issue.
If you can hold over 5 lbs pressure at WOT why go thru the hassel of re-rigging the fuel system?[/QUOTE]

Cause more HP is never enough! It never stops. If its done now youll nevr have to think about that possibly being the problem. (if there is one). Not trying to get yo to do extra work now or sell ya something. Its just that I usually do it your way and try to save money and time and end up doing it the hard way in the end.

Like hp said, as long as you have positive pressure you should not be running out of fuel.

You Did Not Say How Much H.p. You Want To Make.
You Should Increase The Hose Size To 1/2' Even If You Can Not Change Port Size In Tank. This Will Help The Fuel Pump . Now Your Suction Pressure On The Pump Is To High And Will Cavatate It To Death.

I'm looking at probably 600hp after adding 7psi of boost to a 454 magnum. It'll be a fuel injected whipple setup, so i'll need 50psi at WOT. I'll have an in dash fuel pressure gauge. When I do the install I'll look into running 1/2" line to the fitting.

10 gall per hr per 100 hp. @ full throttle.

:eek: Sprag, Let me get this straight........3/8 ID fuel line out of the tank?!? You would never catch one of my engines on it.....It would never support a True 750 HP engine. The only way you may be getting away with this is the carbs are way rich. I have had more "B" and "A" class race engines out on the circuit than anyone and all of them made over 750 HP, all delivered fuel with 1/2" pickup tubes and hose. Theoretical BS does not always work in the real world. You can have pressure at the carb, but not have enough volume to it. The fuel pressure should NEVER drop if the fuel system is correct.