fuel vent size

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RangerRick

RangerRick

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I have a question, Should my vent hose be the same size as the line from the fuel cell to the pump?......Currently I have 8AN from tank to pump, but vent is 6 AN.
I have a fuel supply issue at high RPM, and am trying to look at different options
Mallory 140 pump (deadhead), 8AN to filter to pump, then 6 AN to regulator(mallory), 6 AN to carb......Car will lay over at 3/4 of the track and recover just before finish line....Im stumped.
 
I would think 6 an vent would be fine. However maybe a 10 an from tank to pump would help. Then 8an to regulator. I am thinking that you must have a very thirsty motor. If so then maybe 140gph isn't quite enough. I will be a little surprised of I hear that the vent is the problem. Is this a big block? Hopefully your filter isn't restrictive.
 
Forgot to ask...is the fuel pump mounted fairly low in relation to the fuel cell? It shouldn't t be higher.
 
yea the pump is below the fuel cell........Cell is mounted in the trunk, and pump is mounted on right rear frame.........the filter is a 100 micron, 8 AN....distance from cell to pump is about
3 ft.? only limiting factor going to a 10AN is the pump has 3/8" threads.......... I just replaced a couple fittings on my regulator today...I had 1 inlet and one exit that were the close bend 90*, installed the pipe bend sweep 90*, Read somewhere that they can cause restriction and durbulence, so have to see how that goes. Car is a 67 barracuda FB, 318, air gap, 10/1, .244 @ .050, .501 lift, 750 demon, pocket ported 1.94/1.60 heads...904 tranny with a hughes 4500 stall, 4.56 gear, mopar FBO dist. MSD 6T, Soft touch rev, and dial a timing, MSD E-coil
 
Maybe it would be a good idea to try a bigger vent since it wouldn't cost that much. That is if the new fittings don't help.
everything else sounds like it should feed that engine.
Float level??
Rev limiter on msd??
 
Yea ive checked the float levels, and my rev limiter, I put a higher chip in but didnt have an effect, even unplugged it no change........I have another fitting coming any day, going to increase the vent hose and fitting to 8AN/ 1/2" to match the fuel delivery size. It just makes sense if you are exiting a certain volume of fuel to have the same volume air coming in?
I did notice my current 3/8" vent hose had a kink in it, had to bend a 90*, Ill make it more of a slow sweep...........thanks
 
It does make sense that the volume going out would require the same volume going in. But fluid and air are of different density. Still it is worth a try.
 
What pressure are you trying to maintain to the carb? The 140 pump should be putting out around 12 psi but the #6 hose from the pump to the regulator can be dropping 3 or more psi at full flow rate, not counting any fittings.
 
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