There is one thing to be considered regarding the excess fuel being returned to the tank. With the large volumes being returned (if you regulate down to, say, 15 psi) how much pressure are you causing in the factory return to the tank?

The return from the CP3 is very low (1000 ml p/min if I remember correctly) compared to the Walbro's flow at idle. Is the pressure caused by the Walbro's return flow enough to overcome the CP3's return and in effect halt overflow return from the CP3?

I have the same concern regarding return flow from the head for cooling purposes. Granted there is a check valve in the return line on the rear of the head (looks like a standard banjo but it's not) but the return from the head is even lower in pressure and flow rate than the return from the CP3.

What I'm getting at is, it may be a good idea to run a seperate return line back to the tank for LP overflow return rather than add head pressure to the CP3 and rail return routes.

Just something to consider in the overall scheme of things.

Richard

 

Good questions, Richard.

"There is one thing to be considered regarding the excess fuel being returned to the tank. With the large volumes being returned (if you regulate down to, say, 15 psi) how much pressure are you causing in the factory return to the tank?"

We don't know that yet, for a Dodge anyway. Stand by. We should have some numbers for a second gen shortly.

"The return from the CP3 is very low (1000 ml p/min if I remember correctly) compared to the Walbro's flow at idle."

Yes.

"Is the pressure caused by the Walbro's return flow enough to overcome the CP3's return and in effect halt overflow return from the CP3?"

Nope. The CP3 has internal pressures of 80 to 180 PSI, depending on the volume of fuel it is trying to deliver. At idle the CP3 would have up to 80 PSI to push fuel down the return line.

Furthermore, pressure drops all the way along the fuel circuit, especially across the bypass line because it is smaller and more restrictive than the rest. As long as the Walbro pumps, the return flow from the CP3 will move downstream.

"I have the same concern regarding return flow from the head for cooling purposes. Granted there is a check valve in the return line on the rear of the head (looks like a standard banjo but it's not) but the return from the head is even lower in pressure and flow rate than the return from the CP3."

The ultimate source of that return flow is the leakage flow from the injectors themselves and thus there is lots of pressure to push the fuel down the return line. No worries there.

"What I'm getting at is, it may be a good idea to run a seperate return line back to the tank for LP overflow return rather than add head pressure to the CP3 and rail return routes."

I don't think it is necessary, but lets make that judgment when we see how much backpressure the stock return line has.

 

Hey, in a few days I finally get to become my own "Beta" tester. Once I figure out the electrical relay and stock lift pump replacement plate figured out.