vintage chromoly

iTrader: (3)

I'm using the baker pump. 15 psi with a return style regulator and I'm set for just a tick under 6 psi on the gauge.
-10 feed to the water / fuel filter
-10 to the pump
-8 to the log
-8 log to regulator
-6 return line to the tank.

ICDEDPPL

iTrader: (1)

Dead headed 7-9psi pump and no return I used to run out fuel pressure at 5700, let off it would come right back.

I ran everything in -10AN
15 psi pump baker and tank return. No more issues

MILD THUNDER

iTrader: (3)

That pump simply has a lower set bypass spring, than the high psi version. If you use a deadhead regulator, you simply force the pump to go into bypass mode all the time. If you use a bypass regulator, the pump doesnt have to be internally bypassing all the time.

The 7psi version, is bypassing a majority of the time. Obviously at idle, the pump is no where near moving the amount of fuel its capable of. In order to keep 7psi of pressure, it simply bypasses internally. Once you get to the point the pump stops bypassing internally, (high rpm), you likely would see a change in fuel pressure on the gauge. Not necessarily a bad thing, as a ton of fuel is now being moved, because all the valves are open so to speak (needle and seats).

Theres a big difference in dropping fuel psi because the pump is starving for fuel, and dropping fuel psi because the bowls are filling properly. Keep in mind, pump output decreases with line pressure. A pump with 4.5psi of line pressure, will move more fuel than at 8psi of line pressure. take the pump out of the equation, and yes you will move more liquid thru a line with more pressure, but we are talking about the pumps output capability. And that decreases with an increase in line pressure. Hence why a electric pump that can do both carb and EFI, generally can support a chit ton more power with a carb setup, vs an EFI setup.

getrdunn

iTrader: (7)

I see many with a one per carb as well as some with one per two carbs via twin SC app. I lost that pic again of your set up MT. Also are you running boost ref regulators? I have the fuel blocks and would like to run one 10 AN reg per engine right before fuel blocks.
I would imagine one per carb is ideal but wanted to ask anyway.
john

just thought about it and wondered since your using the lower psi pumps if you even using regulators.

getrdunn

iTrader: (7)

Wonder if you could just run the return to a T on fuel filter inlet rather than tank?

MILD THUNDER

iTrader: (3)

You'll start to see the limits of a single carbs fuel flow capability at a certain to level. My buddy Joe had to upgrade to dual needle and seat bowls on his blowthru setup. It just couldn't keep up with the standard setup

You only need a boost referenced regulator with a blow thru setup. The fuel pressure must rise proportionally with boost on those , because the float bowl is being pressurized. On a draw thru, it's not needed.

As​​​​​​ for mine, I am running -10 from tank to the big wix water separators. -10 from separator to pump. -10 from pump to a 4 port manifold mounted in the back of the blower. Then -6 to each bowl. I like this setup better than the hard line setup, as it allows you to remove bowls for jet changes without needing to take off the bowl inlet lines. Just remove the 4 screws and bowl hangs by the an line

MILD THUNDER

iTrader: (3)

I've never done that , some have I believe. Me and Dan talked about that on his setup, but returning it to the tank makes the most sense.

For one, There shouldn't be a restriction on the return side. I can see where plumbing back into a filter, can restrict the fuel flow. Most modern vehicles use a return line, that goes back to the tank.

Dan returns his to his tanks. The setup he has simply works.

underpsi68

I just want add you have to increase fuel pressure 4x to double the flow. Some think that if you double the pressure you will double the flow. It is not linear.

vintage chromoly

iTrader: (3)

I agree, no good reason not to return the fuel right to the tank.
i plumbed mine to a stainless "T" fitting in the fuel fill hose. I bought the fitting from Teague or Hardin, I can't remember which one.
Anyhow, it makes for a clean install.

MILD THUNDER

iTrader: (3)

I know there's alot of guys running a simple enderle style bypass valve . Clay Smith sells them, like 65 bucks, preset to 7psi. If I was to do the higher pressure spring pump, i would use one of these for my bypass regulator. Simple setup.

By-Pass Check Valve (AN #8) - Clay Smith Cams
I installed a low fuel psi sending unit on my fuel log. I have yet to wire it in to the led warning light on the dash , but my thoughts on that, is who has time to stare at a fuel psi gauge when running balls out ? And chances are by the time you ran out of fuel psi and saw it, the Pistons would be fubared . If it falls below 4.5 psi, the light comes on. Fuel psi gauges, mainly electric but also mechanical, are notoriously wrong. You're talking about differences of 1 psi with such low pressure we run with a carb. I believe mercurys range of acceptable fuel psi on the carb sc engines was a max of 7psi, and minimum of 4psi .

You could still find the NLA holley 6 valve low psi pumps they used on the 800 and 900sc, for around 200 bucks in the mercury box.

Besides baker engineering, C&S specialties also sells this pump with some upgrades to it. Roger at C&S can tell you what these pumps can handle HP wise.