Fuel return line question

LR Max · Post by **LR Max** » Tue Feb 21, 2006 10:28 pm

I've researched but couldn't find an answer.

I am converting a vehicle over from carb to TBI. I've done a lot of reading and I've got a lot of stuff figured out (I think, we'll find out soon enough). One thing I haven't figured out is the fuel delivery and return system.

The vehicle I am installing on has 2 fuel tanks. On top of that, I am not too keen on drilling into any of the tanks. So I was wondering can my fuel return line be tied into the fuel delivery line with a T-connection before the fuel pump? I think this could work pretty good...I guess.

Also, does anyone have any recommendations for an electric external fuel pump for a TBI? I think she'll be running under 20psi (I'll look at the book again). I looked at some from summit racing but they all seem pretty pricey.

Thank you.

Mike_Robert · Post by **Mike_Robert** » Wed Feb 22, 2006 4:02 am

Remember that one benefit of a return type fuel system is that heatsoaked fuel from the rail is returned to the tank; cooler fuel replaces it. With your scheme, you'll be pumping hot fuel around in a circle with only the amount burned being added from the tank. Hot fuel = vapor lock on the rail = car no-go. If you have a vapor line back to the tank(s) those are sometimes acceptable as a return line, depending.

-Mike

hudsonhawk · Post by **hudsonhawk** » Wed Feb 22, 2006 6:19 am

Typical TBI fuel pressure is 13 PSI and is regulated on the TB itself. So you want a pump that can maintain at least that amount of pressure under full throttle conditions. I went with an inline Holley TBI pump. You can also use the inline pump from a Ford Econoline van with TBI. Either of them is going to be some cash. The Ford one is cheaper and can be found at most autoparts stores if you dont like doing the junyard marathon.

I believe the Holley I have is rated at 25 PSI. So it is more then capable of handling the demands of the TBI.

whittlebeast · Post by **whittlebeast** » Wed Feb 22, 2006 6:57 am

My first thought is that the returning fuel has bubbles in it that when you return this to tank the bubbles just rise to the top on the tank harmlessly. With the way I understand your idea the bubles may get sucked in by the pressure pump. EFI high pressure pumps are not real fond of pumping bubbles on the intake side. Google cavitation and gasoline vapor pressure and vapor lock.

AW

Jack · Post by **Jack** » Thu Feb 23, 2006 4:40 pm

whittlebeast wrote:My first thought is that the returning fuel has bubbles in. . .
AW

Where would these bubbles be coming from? I don't see what in a fuel system would create them.

Jack

Mike_Robert · Post by **Mike_Robert** » Thu Feb 23, 2006 4:46 pm

I'm pretty sure that he means that if any air is inducted from the tank (hard cornering, offroad rough ride, etc.), it will end up getting recirculated. The vapor bubble thing is an entirely different phenomenon that is exacerbated by hot fuel.

-Mike

fscott · Post by **fscott** » Thu Feb 23, 2006 9:42 pm

Jack wrote:
Where would these bubbles be coming from? I don't see what in a fuel system would create them.

Jack

The fuel in the rail is under pressure. As it passes through the rail and engine bay, it's heating up. Then it passes through the pressure regulator, and the pressure is released. So some of the components that want to evaporate at the higher temperature are now free to do so, and they can form bubbles.

It's like opening up a bottle of warm soda.

Fred

Jack · Post by **Jack** » Thu Feb 23, 2006 10:02 pm

OK, learn something new every day.

Thanks,

Jack

DieselSJ · Post by **DieselSJ** » Fri Feb 24, 2006 2:55 pm

I know someone that had a setup like that a long time ago (on his AirSensors EFI system) and it seemed to work well. He did run the fuel through a small cooler that was mounted in front of the radiator.