Recently drove a CTD with a 150 gph FASS installed. (I have a 95 gph).

Guess I don't understand how the FASS works as well as I thought! The 150 gph looses the same 1 to 1.5 psi when you go to WOT that my 95 gph does.... even with over 100 hp less? Not a performance problem... just surprising. Both come back up (2-3 sec) as pressure rebuilds... but I thought the 150 gph pump would not do this at all?

Make sense to anyone?

RJ

 

Well if you believe the whole its not pressure but volume thing....Im used to gassers where when the pressure rises,so does the volume.Im sure that a 150 would flow more with bigger lines.Im also sure the supplied 3/8 line that comes with a FASS is a bottleneck between the 2 systems making them equal.I say that with no proof but if you think about it it makes some sense....

 

In this case, it doesn't matter if the pump is rated at 20gph or 20000gph.

They will both lose pressure.

This is because you're talking about a static system.


To maintain absolute rock-solid FP, you need a bypass regulator, which is DYNAMIC and can account for varying demand conditions.

No time to explain all the details now (not sure I could)-- but a BYPASS regulator with its own return line is the only way to ensure constant FP with such widely varying fuel demand.

jh

 

Thanks...Static System...Got it!

 

Look into the Aeromotive bypass regulators-- they have a couple that are diesel rated.

Unfortunately, they only have a carb regulator that goes UP to 15psi, and a EFI reg that STARTS at 40psi and goes up to 70.

So if you want a diesel-rated regulator for the area between 15 and 40psi, it appears that you're out of luck.

I'd recommend a call to Aeromotive to see if they can't use a custom spring in one of their Marine regulators to let you get 20-30psi.

At least, that was MY plan


BYPASS REGULATION!!

 

As I mentioned above...it's not a performance problem...as far as I can see. It was just an academic question to better understand the system.
As far as I can determine...I still have more than enough flow... even with a 3 micron fuel filter.
I'm speaking from how it feels (and how gauge reads). Would you disagree?

RJ

 

No, you have plenty of fuel.

The momentary drop in pressure is just a result of the system adjusting to the change in circumstances (fuel flow/demand).

jh

 

Sorry, but I'm confused again. So why are you interested in a bypass regulator?

RJ

 

Mallory makes a return style regulator 4-25 psi the summit part number MAA-4307 they told me its rated for diesel $100. I was going to go with this but have since changed my thinking will be going with a valve in the supplyline after the VP plumbed back to the tank and adjust presure to about 15psi @ idle and let the rest of the fuel pass the supply for the VP, as it will only take in as much fuel as it needs anyway.

Jed

 

Fuel pressure regulators for the TBI Chevy Motors should be in the same range........they needed about 12-15 PSI to work correctly. But its an aftermarket thing. They dont have them stock.....since the fuel pump is at the correct pressure.....

 

A bypass regulator is the only way to keep a constant, unwavering FP reading on the gauge. *IF* that's important to you.

No one's saying that you have to have absolutely constant FP. A momentary drop of 1-2psi isn't going to hurt anything at all.

To me, a bypass regulator is the way to go, but NOT because it gives constant FP (which you don't really need).


Instead, a bypass regulator relieves a lot of stress on the pump when it has to pump "deadhead" or, worse yet, self-regulate by just pumping fuel within itself.

With a bypass regulator, the pump sees a constant workload. THIS is what's important (imo) for pump longevity. This also means that the pump is constantly getting cooler fuel at it inlet instead of pumping the fuel inside itself into a froth.


As an added bonus, you could plumb into the return side of your regulator some additional, higher-efficiency filtration, provided it had adequate flow to not restrict the return side.


With the above system, you'd have:
1) constant pump workload
2) Constant fuel circulation
3) Constant high-efficiency filtration


All are, imo, good things.

 

I thought a read a post of that Mallory regulator giving up the ghose when used with diesel....but maybe that was a Mallory PUMP, not a regulator.-jh

 

Thanks, Interesting Information!

RJ

 

The FASS and HPFP pumps both have a regulator at the Gerotor to keep the motor alive under a Dead head condition (This was implimented to keep a dirty filter from burning up the motor). The older FASS systems (Like the one i have in my ride) do not have this regulator set up. Also it will by-pass into the return side if pressure becomes too great on the engine outlet.

 

how can you tell which one you have? Old version or new?