just talking to a chevy guy(that hurt) who has a blow through small block and i was explaining how my engine was hurting head gaskets at higher rpms and he said the my fuel system was not keeping the fuel bowls full because the fuel lines need to be at lease 1/2in to the regulator and that i need a boost control regulator to increase pressure when under boost and a 160gal/hrs pump. i have a 4-71 blower with a 750cfm mech secondaries driven 1to1, i have 2 carter 72 gal/hrs pumps and a single regulator set to 6lbs,my fuel lines are 3/8in from the tank to carb, the 2 pumps are run in parallel so one is not feeding the other, i can see the boost referenced regulator helping at full boost but the 2 pumps i am running should keep up with this 750cfm even on a blower,does this sound reasonable? i think 144 gal/hrs flow should be enough, anybody else have any ideas thanks.

You're probably way lean. Even though the pumps are 72/gph they cannot overcome the boost that the carb is seeing. If they put out 6psi and you are getting 6psi boost your carb net sees zero fuel flow because they net each other out. I have a 3/8 supply line to a mallory boost referenced regulator (1 to 1) and a 3/8 return line. It is driven by a Walbro 392 pump. I agree with Jess from another post that you are way lean.

Sorry, I missed the blower part. I'd think one pump would suffice. Did you check your fuel filter? A friend of mine had a lean condition on a EFI 440 and it turned out to be a fuel filter. Even though the system was new, there was contaminates just from the first use. He was using a 10 micron filter. Swiched it out and all was fine.

thanks, a fuel filter would`nt hurt to try, on the blower, my is a 4-71 witch draws through the carb, the guy i was talking to has a blow through carb, his is also a 750cfm but i was wondering if his problem is because the carb is seeing boost pressure my is not.i just trying to cover all the bases but my fuel system i thought was good enough, 2 of these pumps should be lots if there working right.lately i have been checking that much going down the track i never noticed the fuel pressure but at the start of these leaning out problem i did check it and it was holding at 6lbs on the gauge,if i get next weekend in i can make a note to check fuel pressure again. thanks

Draw throughs don't need boost pressure referenced regulators, and should not use them. These only belong on blow through setups. More Chevy guys giving bad advice... it's almost enough to make me embarassed to own a Corvette.

If the fuel pressure is not dropping at high RPM full throttle passes, it is likely to be a tuning problem and not a fuel delivery issue, since the first sign your fuel delivery is inadequate is usually that the fuel pressure drops. I'm not as much of a carb guy as an EFI one, but I wonder if the power valve might be an issue here.

_________________
"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

i have 4in/lbs vac at idle so i have installed a 2.5 power valve in the 750cfm carb,one thing i have not checked is the channel restriction,when i had the 2/650cfms on the blower i had power valve blanks,once i get to the point were i am to rich on jetting or can`t get enough jet maybe opening up the channel restriction might help. also i can`t find out if the o2 sensor i am using is a wide or narrow band, so for now i will have to not trust it .

If you don't know, it's almost certainly narrow band. But here are a few tip-offs about which is which.

1. Narrow bands have four wires or fewer; widebands almost always have more.

2. If it came with a gauge, a narrow band's gauge is likely to read "Rich" to "Lean" while a wideband will usually read real numbers. Not 100% reliable as you can pair a wideband sensor with a narrow band gauge.

3. Wideband sensors often have a control box between the gauge and sensor.

One other note: If you have a narrow band sensor and it's reading under boost, that is a reliable indicator that you're seriously too lean. A "Rich" reading might not be rich enough, but a "Lean" reading when you shouldn't be is virtually always too lean!

_________________
"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

My wide band has 5 wires and the narrow that I had, had 3. Also, check your power valve. Some have larger channels to flow more fuel. On my blow thru I'm running a 600dp, 70's in the front, 82's in the back and the PVCR is drilled to .075". At 20psi this is netting a 10.9 afr. Rich but safe.

will i think i can safely say i have a narrow band sensor and right off the line it reads between 800mv to 980mv but i am usually lifting be for the end of the track because you can feel the power loss.thanks, something else to try and iron out, it`s been a fun summer if i could only get my 11et instead of having to lift on 12.00et runs

On a draw thru system, the power valve should be referanced to the intake manifold, not the base of the carb. It is possible for the manifold to see pressure, and the base of the carb to see vacuum, especially if you back off on the throttle.

_________________
Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

so charlie would it be better for me to plug the power valve and jet it up #6to #10 jet sizes?

Can't help with that question. I have always used a power valve.
On the big Holley 2 bbl, it is not hard to reference the PV to the manifold. There is a passage in the base of the carb that goes up to the power valve. At the same point in the base of the carb is a manifold vacuum port. I just took a small piece of plastic tube, like the kind that comes on a can of carb cleaner, or brake kleen, coat it with some silicone lube, and stick it in the vacuum port from the outside. The take some epoxie, and fill the passage in the base of the carb. When the epoxie dries, remove the plastic tube. Now you have a passage from the power valve to the outside of the carb. Connect a piece of rubber hose to this port, and run it to the intake manifold.

_________________
Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

charlie i have taken out the power valve and put one of the plugs i had from the 650`s that i ran before ,i did not want to modify this carb because it worked so well on the high comp engine and i want to put it back on it when the street car is finished, so i jetted it up #6 to #92 prime &#96 secondary, she super rich at idle now so at least i can work from there if i get to the track, i still think the to 650`s were the best (60fts/ 1/8 mile,ets) if i can trace the high gear full load problem with the head gasket failing with the 750 carb maybe i will go back and try or maybe i won`t depending on what happens with this colder plugs/steel head gasket& insanely rich mixture