i'm running a mallory 140 with -8 to the return style regulator & -6 to the 930 cfm carb. on alcohol. no problem. gas should really be no problem since 1/2 the volume of fuel is required compared to alky.
7 1/2-8 psi.
S/ST 1818 S/P 1018 H/R 1564
<font size=-1>[ This Message was edited by: igo1090 on 3/14/06 4:38am ]</font>
I run a Mallory 140 with the return regulator (placed after the carb), #8 in both directions with 3/8 tube to the bowls. Big RCI fuel log. Pressure is set at 7 psi and it never varies. Good setup, well worth the hassle to purchase and plumb. 5 years and counting on the pump - I'll eventually get my money's worth out of 'em.
It's really a backpressure valve...that is, it keeps the pressure behind it constant and bleeds off the rest to the return line. If the float in the carb shuts the needle and seat then the pressure in the line goes up, then the regulator opens and bleeds the pressure to the return line, if the float drops and the needle and seat open, then the pressure behind the regulator drops, so the regulator pinches down to maintain the pressure behind it........it's really the best way to maintain full flow to the carb no matter what.
Comp 140 return system is good but watch your volume at lower pressures and high hp.
I use a mallory comp 140 and a holley blue at the same time on a return style regulator set to bleed off at 6.5 psi and it worked great with duel pumps, but one time on the dyno I forgot to turn on the blue pump and the motor was cutting out around 400RWHP from lack of fuel VOLUME. Cranking the mallory regulator to 7.5 psi for the motor sovled the problem with running only one pump. But 7.5 is too much for the n20 system so I set up a seperate holley dead head regulator after the return regulator to adjust it down to 6.5 psi for the n20. 2 pumps is a great way to keep from burning up a big motor due to lean out from pump failure or fuse poping. It doesnt take much to stop a mallory pump because they have tighter tolarences than holleys. I popped a few fuses from fuel cell deteration but the holley keep on pumping when the mallory gave up.
We have ours exactly the same as 392Bird has his. We're running a Comp 140 with a Mallory 4309 regulator and all 8AN plumbing.
The old deadhead regulator setup was giving us trouble with fuel supply so we switched and it made all the difference. The pressure stays steady as a rock at all times and the return flows like a garden hose,proving the Comp 140's capacity. The fuel at the carb is always cool and always moving so as soon as the needles open,it's in there. Best thing we ever did.