AN-6 or -8 for My Fuel System (SBF)

[FireSale]

Originally Posted by Bill Edgeworth

I have seen a couple things that I would deem as problems created by oversized fuel systems.
Hot fuel on systems with real big lines. If you are using real big lines on a low horsepower application the flow velocity is quite low. So when you throw a #10 system on a lets say 350hp motor the fuel takes a long time to get from the cell to the carb. Most of that time its spent in a fuel line that is probably routed through areas exposed to a fair amount of heat either radiated from the ground, exhaust or engine compartment. All I can say on this issue is if you insist on putting a system in your car that could support 1000hp make sure it’s well insulated. I should also add putting in way too big a pump generates heat in the fuel.
Another example of better isn’t bigger is a problem a friend faced on his modified car a few years back. He decided to freshen his carbs and afterwards had a huge problem with the car stumbling after the launch. During the freshen on the carbs he figured what the heck he might as well get all the good stuff from Brasswell. He spent big bucks on their bowls and needle and seats. Figured bigger was better. Turned out (and I understand C-25 is especially bad for this problem) as the floats dropped and fuel started to flow after the launch the inrush into the bowl was so great that it causes spill over into the boosters. Not sure if it was foaming or just the flow being so high that it pushed the fuel into the boosters. Moving the floats up or down did not help. He took the big Brasswell needle and seats out and put the smaller stuff back in and the problem went away. Guess the lesson here is don’t use Pro Stock carb parts on a 300 inch motor.
I know in my car running 11 teens in H I used to just run a Holley blue pump with no problems the data recorder showed no fuel pressure or O2 issues. I decided to upgrade to the Magnafuel 300 when the Holley was getting a little noisy and immediately started having problems with the hydraulic shock at start up overpowering the regulator and the Q-Jet. Took a bit of work and a real light regulator spring from Magnafuel for the bypass on the pump to solve the problem.
Adger touched on the subject talking about orifice sizes; there is not much point in having fuel lines 20x the size of the flow orifices in your pump, regulator or needles and seats. The system needs to be big enough to not cause excessive pressure drops but way bigger could possibly cause you some grief.
My .02

Makes a lot of sense. Efficiency is important.

Thanks.

Dale