Dual Fuel pumps in Parallel, one on Hobbs Switch

[Ondonti]

Since I have a lot of fuel pump capacity but undersized injectors, I was thinking about running higher base fuel pressure to make more power (at 90%+ IDC already on low boost numbers with E70 and its gonna get worse because I moved back to an E85 state so my injectors will behave even smaller).

The idea of running high base fuel pressure all the time scares me.

My current fuel setup is twin OEM 5/16" feed lines being fed by twin external Walbros. Enough for 1000whp on Gasoline. Maybe 750whp on E85.

I was thinking I could set the system to run on one pump out of boost, then have a hobbs switch set to zero psi and have that activate the second pump. I previously ran these injectors well over 100psi with my old rising rate regulator setup so it wouldn't bother me to hit 100+psi fuel pressure when the second pump turns on.
It will turn my little 36# injectors (they are actually 47# but E85 turns them into the equivalent of 36#) into 54# injectors at 100psi and 57# at 110psi. I know flow gains drop off a lot at high pressure but with the fuel pumps to handle it, it would be a cheap way to make more power without getting new injectors.
I really want injector dynamics injectors if I upgrade and they are 100 a pop. I am pretty sure six 54# injectors plus 2500 cc's of methanol is enough to max out this stock shortblock. Possibly allow ~180whp more to be made without changing anything.

I could constantly run 100psi but I just don't like the idea.

When setting things up I would just set fuel pressure with 1 pump and see how high it goes when the 2nd pump turns on. Then adjust the regulator on 1 pump until I get the fuel pressure I want on 2 pumps. One thing is that I don't know if my Trick Flow regulator (probably the same thing as every other 2 in 1 out regulator out there) wants to do 100psi. I think it claimed 30-70psi but I don't see why it would be a problem since I think that range is an "estimate" based off what they think is reasonable on the average setup...?

I also have no idea how much pressure might change when I make the 2nd pump go online..........I know how my old RRR and base regulator worked, it was just a metal diaphragm pushing against a seat. Pressure was created by a restriction but it was only stable if fuel pump flow was stable (in my understanding).
Not really sure how this one regulates pressure.

[Vigo]

I am pretty sure all the non-rising-rate ones work the same.. just a spring behind a diaphragm pushing on some sort of valve. I think you are right about the stability thing, in that when you turn the second pump on there will probably be some kind of 'spike', but i would guess it would only be a fraction of a second. In fact,i dont know how hard of a hit it would be because when i jump power to a stock fuel pump while watching the fuel pressure, it only bounces up 2-3psi if the system is already pressurized..

Anyway, it MIGHT cause some kind of rich spot you'd need to tune out, but i think it will be minor.


As far as running it off a switch, that part seems easy. You should be able to just order a switch that would work and then run a relay to the fuel pump with it.

[Ondonti]

Well if the regulator will just bring back fuel pressure after a spike then its not very useful I guess. I still have my rising rate regulator and this would work well with that but not so much on a standard regulator. If you remember, my RRR wouldnt get pressure low enough with twin pump until I ported out all the passages in it. Those dual pumps are much happier with RRR high pressures, and I could set the ratio really low. Not something I want to install again but something someone else could do :P

[Vigo]

The only reason pressure would go up from a 2nd pump coming online would be if the regulator orifices were too small to bypass the increased volume.. although like a wastegate the more fuel the injectors are using the less has to be bypassed at a given total volume.

If you wanted to run different fuel pressures in different condition ranges you'd need to run 2 fuel pressure regulators and a fuel solenoid. It could still be done.

[Ondonti]

And overrunning the oriface would just result in a pressure spikes that would be relived by increased fuel demands, making the process stupid :P

Might still play with it to get rid of the fantasies.

[Vigo]

Might still play with it to get rid of the fantasies.

you know, noone treats that as legit but i totally understand! I dont care how much theory/reading there is. If something seems interesting (especially the learning part), i do it even if it doesn't fit anyone else's cost/benefit ideal.

[1BADVAN]

If you wanted to run different fuel pressures in different condition ranges you'd need to run 2 fuel pressure regulators and a fuel solenoid. It could still be done.

Thats what my idea was

[Ondonti]

i just hate having those irrational fantasies about some car thing. They need to be obliterated with testing ;)

[Speedeuphoria]

describe your parallel setup. Is there a checkvavle on the other line that will be only used in boost? If not you would have bleed back from the other line/pressure