Hey guys
I am planning on putting a Holley on my 1980 and had a question on fuel lines. I will be using the Mallory 4070M and was wondering if the stock fuel line is up to the task or if I need to go 3/8" as recommended? I would prefer to keep the stock for simplicity and affordability. Also, can I just run the pump straight in at 6 psi or do I need a pressure reg with a return line?

Thanks

 

The stock size is fine.

 

Thanks. Will make install much simpler.

 

you will need some adapters for the regulator, but do try to use the factory return line.

 

OK, I was planning on using the pump's internal bypass as I bought the Mallory. Is that ok to not run a return?

 

It can, but the internal bypass isnt perfect. A return style regulator is. I actually had both for years, a fuel pump that bypassed internally (Holley red@6psi) and a bypass style regulator. The holley red was so loud that you could actually hear it bypass itself as it made a different pitch. Over a short time, I had a series of fuel system failures (worn pumps, flooding on startup, flooding over bumps, etc) from the bypass'd pump car, and no issues with the car I was running a bypass regulator on. Coincidence? Maybe.

You see, measuring the fuel system's pressure at the pump way back under the tank of the car isn't a very good method of determining pressure at the carb. (Where you need accurate measurement) In reality, fitting choices, bends, hose styles, and even the size of needle and seat you are running could make the pump "think" its time to bypass, since at its end, it is feeling 6 psi. But, at the carb you are only getting 4 psi after the length of the fuel system and its variables.


If the pump you own is an internal bypass style, feel free to use it and post your results here. User feedback is limited, and often very exaggerated here. All too many times have people claimed things to be "perfect" when in reality things are far from it.


My suggestion is to run a bypass regulator alongside your already bypassed pump, just to avoid some of the common creeps and gripes of deadhead style fueling holley carbs. Having an always flowing, functional return system like Mazda designed these cars to have in the first place has always been the most reliable method for me.

 

Makes sense.
Thanks

 

just to add another data point, i'm running the stock fuel line and its totally fine.

Mazda gives fuel delivery specs for the P port engine, and i'm basically right there with the stock line, and carter pump.

 

Which carter did you use? I was just telling someone this a few days ago and they are in disbelief that any carter could fuel a pp.

 

the 6psi/72gph one. installed in the car its only doing 4.2psi and like 38gph, but that is basically what Mazda specs for the PP.

the BSFC is better with the P port, so per unit of fuel, i make more power than you!

 

Im running that on a stockport right now and this has me thinking mines broken lol. I have trouble feeding a 465 holley on a stockport with it, but I only just started troubleshooting to see if its really the fuel pump or a clogged filter. Both are new, but I was sure that we had the same pumps anyways haha.