Podium

Ive seen guys run 43 and 58 psi. Im going to run twin intank 340 pumps, one with a hobbs switch with 8 an and 6 an return. I see that I can get away with less injector but more pump if I run 58 psi. I can do less pump and more injector if I run 43 psi. Am I correct?

Shooting for 600rwhp on e85 but also want to plan ahead for the built motor. It will be almost driven daily in the summer. probably 750 to 800 in a few years.

Also looking for thoughts on boost reference. Some people do it, some dont.

Podium

Looks like 80s for 58 psi and 90s for 43 psi for 800 to the wheels with e85.

BLWNZ

You have it backwards. More pressure less pump flow but more injector output.

robert miller

glennd

Yes you are correct you can pump more flow at the lower pressure.
However if you are not boost referenced, the pressure across your injector will be getting pretty low under boost @ 43 psi. Example, at 13 psi of boost and 43 psi of fuel pressure, you will only have 30 psi across the injector. I would recommend a 2 pump system @ 58 psi.

Podium

I plan to use boost reference. Are you saying 58 psi with or with out reference? Just want to understand and weigh the pros and cons off both.

TTBlueZ06

If you try to run 43psi the fuel tank transfer system will not operate correctly...
It uses high pressure, low volume fuel to create suction using an eductor style "jet pump" in the passenger tank. Without enough pressure, it doesn't work and you will just drain the drivers side tank while your gas gauge reads half full...

TTBlueZ06

You want to run 58psi base pressure and use a boost reference regulator with a return. Base pressure is set without manifold vacuum, so it will drop slightly once you connect the vacuum/boost line too it.

Podium

Thanks! Good to know. Im new to Vettes as well and this dual tank thing. You saved me a major headache! Fuel injectors are also cheaper if I run 58 psi lol

Milan

You don't have to boost reference if your injectors can support the flow.

neutron82

my base pressure was set to 46 when the tune was done and I haven't had any issues with the siphon pump not working... there is a point where the lower pressure will become a problem as stated above, I'm just not sure where that point is... I have seen the siphon pump issue worked around before but it was pretty involved and totally unnecessary for what you are doing

glennd

I ran boost reference and set up fuel pressure at 50 psi atmospheric. I was doing a mileage check on a trip, hence no heavy acceleration. The manifold was probably running at 7lbs vacuum (educated guess). So with approximately 43lbs pressure I ran out of gas. The fuel did not transfer from the passenger side tank.

TTBlueZ06

This was my experience as well. Im about to bench test a new system using a .060" orfice feeding the transfer system and im going to see exactly how little pressure I can get away with and still transfer fuel. Then I am going to play with the orfice size and see if it makes a difference. Running such a high base pressure in a boost referenced return system is stupid, has to be a work around for it.

FEAR LS

Exactly!

Bryan@MCS

I disassembled a transfer jet pump out of a '99 fuel tank and measured the pressurized fuel orfice with some pin gauges. The orfice only measured .017 (seventeen thousandths). Any upstream orfice or restriction on the high-pressure fuel feed should not affect the transfer pump until you are at or below that size.
Also, a -3 hose should be large enough for the pressure feed to the transfer pump. A larger hose (-6) is needed for the low pressure return flow to the left-hand tank.

TTBlueZ06

Interesting findings. For the last 8 years ive been running the system with a .060" orfice feeding the pump and it has worked flawlessly. When I bench test the system I will remove the orfice and see if it still works with a direct flow as you are saying. I replaced the feed and return lines with -6 lines 8 years ago when I built this first fuel system so those should be able to stay. Still my goal is to lower base pressure and still get it too transfer. I don't like running 58psi as a base, too much stress on the pumps when you are making 20+psi of boost.

Podium

I would have to buy injectors that I bigger than I really need then correct? For example if I ran 90s at 58 (80 duty cycle), I would probably have to get 120 to cover it if I didn't use boost reference to compensate for the drop in psi as boost rises? I could use the 90s if I use boost reference.

FEAR LS

Example: I plan to run 95lb injectors @58psi. The differential pressure at the injector (which is now 45psi) is going to make my 95lb injector flow 84lb. Which on 93 octane is going to be plenty.

PM me your choice of injectors and setup and I can help you work the numbers and give you ball park figures of where you would be.

-James

Podium

Thanks, that's what I thought. I'm going to use e85, so I'm thinking 58 with boost reference is the way to go. I want to plan for 800 max on corn. I should get away with 90lbs at around 80 duty cycle if I'm at 58 psi with boost reference.

FEAR LS

You will just have to ensure your pumps can handle the differential pressure. Meaning if you're running base pressure of 58psi and boost referencing the pumps, at 13psi, the pumps will be trying to push 71psi. A lot of pumps lose flow dramatically at that pressure.

So you would need some really good fuel pumps to push e85 at 71psi.

Game of give and take...

-James