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Tech Information => EFI Questions => Topic started by: n49racer on May 17, 2017, 03:35:11 PM

Title: EFI Return Line Placement
Post by: n49racer on May 17, 2017, 03:35:11 PM
Hi All
We are having a discussion about fuel stalling in the feed line on acceleration. Our car (AA/BFRMR) has the fuel tank mounted behind the engine. There is a -16 feed line to the belt drive mechanical pump (approx. 3 ft long). We are concerned with fuel stalling in the feed line on a hard run.

We currently have the return line -10 from the regulator back to the tank but are wondering about running the return to the inlet of the pump to help alleviate the perceived fuel stalling issue. Has anyone tried this setup or have knowledge on this issue?


Title: Re: EFI Return Line Placement
Post by: SPARKY on May 17, 2017, 04:08:46 PM
If you are consistently  returning more fuel than you are using might consider a high volume low pressure pump in the tank feeding the mechanical would give you more peace of mind

Title: Re: EFI Return Line Placement
Post by: Stan Back on May 17, 2017, 04:52:38 PM
I know the problem.  I ran Enderles for 40 years on the street in my roadster.  And I would "run away" from the fuel.  I solved the problem with a small tank in front of the engine with a carburetor float device to control the level in the front tank.  Pretty Mickey Mouse, but it did solve the problem.  No room at all for a small front tank?

I put electronic fuel injection on my '54 Plymouth.  I still use the back tank, but pump up the reservoir hopefully shown here.

I'm thinking you guys got the "World's Fastest Street Roadster Pickup" or such.

Title: Re: EFI Return Line Placement
Post by: Stan Back on May 17, 2017, 04:55:40 PM
. . . and then, actually thinking about this, you'd probably need a whole lot more fuel for five miles that I'd need for a block or two.

Title: Re: EFI Return Line Placement
Post by: Ron Gibson on May 17, 2017, 05:10:28 PM
On running the return to the pump- if there is any cavitation then part of what you will be putting back in the pump will be vapor instead of liquid. Not desirable.
Sparkies idea is best. Just make sure the pump has enough capacity to pump all the volume you can use.


Title: Re: EFI Return Line Placement
Post by: kiwi belly tank on May 17, 2017, 06:13:06 PM
Your concern is well founded. With tank location & 3ft of -16, I'd lay money on the likelihood of you starving the pump on a AA/BF engine. The sheer weight of the fuel will be the problem, it doesn't matter how much pump you have if there's no fuel supply.
There's only one right place for fuel return & that's at the top of the tank.
If you can't correct the tank location & line length you might have to boost pump the supply.
Waterman does cable drive pumps that can be put at the tank but I don't know they make anything for the Little Bertha.

Title: Re: EFI Return Line Placement
Post by: n49racer on May 17, 2017, 07:23:26 PM
Thanks for the replies guys. As of yet we don't have a problem but running methanol on a big engine requires a lot of fuel. The pump at the tank may be the answer. We will be trying to get in the 350 range this year so the acceleration rate may be a problem. A lift pump might work but at that point it would need to be as big as the main pump.
I heard that Poteet had a problem last year as he runs a similar set up.

Title: Re: EFI Return Line Placement
Post by: Rex Schimmer on May 27, 2017, 02:40:40 PM
Don't use just one "charging" pump, use as many as you need to ensure that their pump volume is at least 125% of you engine's pump at full flow. (what is the max rated flow of the main pump?) If you use multiple pumps each will need its' own inlet at the fuel tank which can actually be a large tube connected to your present -16 connection and each pump can be connected to that tube. Make it large, 2 inch would be my starting size. Run the outputs of each of the multiple pumps through a low pressure check valve, 1 psi would be perfect, then combine the flows together and run to the inlet of the engine's main pump. Just before the connection to the main pump you would need to tee in a 5 psi check valve that returns to the fuel tank, this will maintain a 5 psi head on the main pump inlet and allow extra fuel from the charge pump(s) to return to the fuel tank.

Regarding running the return line from the injection system back to the pump inlet, this could be made to work but as mentioned before there is certainly a chance of cavitation of the return fuel through the main return jet (I am assuming since it is a Blown Fuel engine you are probably running a constant flow type of injection system)which could cause the main pump to also cavitate and this type of system would become less effective as the engine consumes more fuel and the return amount become lower volume then you are back to the root problem of not enough fuel to the inlet of the pump. Pump inlet fluid velocity should not exceed 5 feet/sec and using a -16 hose that would be about 12.5 gpm which is probably less than your fuel pump, simply going to a -20 house would make the flow rate, at 5 to/sec, about 19 gpm and a -24 hose the flow rate would be about 28 gpm. This all brings up another problem that many don't consider and is a great reason to use a charge pump system, that is that there could certainly be a possibility that your -16 hose may have the potential to collapse from the vacuum created by the engine pump inlet and most of the stainless steel wire hose that we all use is not rated very high for vacuum use.


Title: Re: EFI Return Line Placement
Post by: POPS on May 28, 2017, 01:06:52 PM
Your braided line WILL suck flat at some point.  It will ruin your speed week.
Use XRP hose with their internal flat spring. Super fix!
Install a pressure transducer on the pump inlet. If there is a vacuum, there is cavitation.
Racepak has suitable transducers.