I’m tuning a set of six pack Holleys so I’d thought I’d try one of those braided line kits from Promax with a built in fuel gauge. My Carter pump that I’ve had on the car for years went up to 8-9 lbs! So I dug out an old Stewart Warner gauge and it reads a steady 9 lbs as well. Seems like I had to get the fuel inlets and needle and seats very tight to keep them from seeping. I also have to turn the the needle and seat way down to get the proper fuel bowl level. I don’t think it’s blowing the needle off the seat at 9 lbs but that sure is a lot of fuel pressure for a Holley to handle. I even tried another used parts house pump I had around the shop that came off a customers car. It was only about 5-6 but before I could really work with that one, I noticed that the pump was leaking all over the floor under the car! That was a scary moment till I got it cleaned up. I thought about trying one of those Edelbrock pumps that advertise 5 psi but flow 40 bpm, but they are pricey at $200. Any thoughts or comments?

The Promax kit with the an fittings leaked. With his supplied aluminum gaskets, it was terrible. I’ve never used those AN fittings before. What is the normal gasket for those that are a direct fit to Holley fuel inlet? I wonder if they use an o ring as well?

6paks came from the factory with a 8-9lb pump, BUT they had a .060" return orifice in the vapor separator that helped control fuel pressure. i just went thru a high pressure fuel thing with one of my street cars. anything over 7lbs can cause problems and seems that 6-6.5lbs is a sweet spot. i use the 6903 pumps and do some mods to them but run a return of some sort. i also think large needle and seats can be a problem with higher pressures. the floats just can't control the flow, especially at WOT. i don't know your power level but stock 6pak fuel lines with the separator can handle 450hp. if you want to keep the braided hose then try to rig up a return line. i prefer hard lines myself, but braided may be better for someone pulling a lot of maintenance.

Most people run a lot more pressure than they really need.

Don't use Chinese hose and fittings.

If you've ever watched a video of 7 psi entering a Holley fuel bowl you would be amaszed. It looks like spraying a garden hose into a dry wash bucket. 5 psi is much calmer. The key is to make sure that you can keep 5 psi constantly.
Doug

i've got a friend with a big cube oldsmobile who went thru the over kill thing. down sized the fuel delivery and he's very happy with it.

i believe it!

The vapor separate comment is misleading, because Mopar fuel pressure spec was measured at inlet to carb and included the separator as part of the system. Hemi pump was 7 to 8.5psi, the 440 HP was 6 to 7.5psi. Mechanical pumps are constant volume pumps. If the diaphram or the airdome age and harden the pressure at outlet rise because less give/expansion of the rubber to buffer the pressure pulse.

I put some BLP Bottom Feeder needle and seats in my junk and turned fuel pressure down to 4 psi.

Mancini sells a Carter street pump that is at 6 psi or so, I need one for a SB but they only make them for BB.

have you ever had your hands on this stuff and worked with it before?

The smaller the needle and seats will allow more pressure before being held open by the fuel pressure. The Holley brand needle and seats .090 will hold 9.5 lbs. pressure is what I have used in the past, the .130 won't hold much above 7/0 lbs. pressure.

i looked at the promax braided lines some years back and for me i thought it was a little cumbersome. so i thought i'd do a 3/8" hard line. going to 3/8" from 5/16" isn't as straight forward as i thought it would be but it did work. down side is no return line because i eliminated the vapor separator. i did make a fuel log for a 6pak once for a friends bracket car that had 1/4" pipe thread on each end where a return could be used. i don't think a log would be difficult to make and may be more maintenance friendly for a true performance car. i have one of those 4862 pumps and did some testing on it. i was very surprised that the pump did do 8-9lbs and would pump a gallon in 30 seconds. i didn't use the pump because i didn't find a regulator i thought would was pulse pump compatible. would i did do was test return sizes to see if i could regulate the pressure like factory HP 440's and hemi's. what i found was it could be done. i used holley jets as flow orifices and something like a #77 jet could get the pressure down to a manageable 7psi at a simulated 2000rpm. i also tried flow testing the vapor separator thinking there might be some restriction there. if the separator is made correctly with a screen they don't give up much if any, and i only tested at 3psi.

many decades ago i was taught larger needles and seats tolerate more pressure; that is wrong! smaller needle and seats are far more manageable.

When I switch to E85 on my S/P car I was told to use a minimum of .130 with stainless seat and needles and less than 5.5 lbs. of pressure. That was a good combination

you would need the volume with e85; thus the .130's.

Well this is a 340 and no return line from the factory. The carbs are 440 carbs and going on a 440. I’m testing to get them leak free and close enough for the customer to tune them to his combo. I don’t have my 440 test motor done yet. The Promax was not the easy install like my old test fuel lines. My needles are .110 Holleys.

Yes in great detail documenting fuel pumps and rebuilding them. I have several dozen disassembled and bagged, what do you want to know. Your comment about large and small needles should have been obvious. The same as MC bore. You apply pressure to a surface area. Multiply the area by the pressure and that tells you the force applied to the area. A set pressure against a larger needle means a larger force on the needle. Hence a smaller needle and seat sees a smaller force for a set pressure and therefore less force opening, which means the float can handle keeping the needle shut. High school physics.

The same applies inside the fuel pump with the different size chambers, size of the washer plates, and thickness of the air dome gasket.

Original carter carbs were designed for a higher pressure, and Chrysler made the move to higher pressure in the 50s. Higher line pressure keeps the fuel in a liquid state when engine compartment gets hot. Less vapor lock. Plenty of good info in the Carter manuals and old Army tech manual.

i have one 6pak left and think about using it again from time to time. if i do it will have .101" needle and seats vs the .110" as factory installed. i wouldn't be afraid of .097" with a 340. return lines aren't difficult to install and really are a plus for street driving. i believe there is a vapor separator for the small blocks but you'd need the factory 5/16" fuel lines. the real issue with 6paks is the screwed up idle circuits. if all your doing is racing maybe you can just do the basics, but for good street driving you really have to go after the emissions built into the circuits.

Could you elaborate on this statement. Since this is my thread, I guess it’s ok to highjack it. I have to agree six pack are harder to tune than most. The factory plugged up the idle adjustments screws for the outboards and the center metering block can give lots of trouble with the idle well tubes. The new bilet metering blocks really help the idle circuit, but they don’t look Stock. I’m all ears.