Fuel System Advice

[MtBraun]

I've tried this with FB pages and am getting very different suggestions. I am running a carb'd 632 in my 84 K10. I want to run the stock dual tank setup with in tank pumps and of course a switching valve. The questions I would appreciate your feedback on:

Are the stock size lines (3/8 feed, 5/16 return) large enough?
Will the stock switching valve work?

Based on my calculations, I need about 75gpm at 6psi.

I realize with an in tank pump I'll need a FPR. Any recommendations?

 

[squaredeal91]

Those fuel line sizes sound good to me,
Holley makes nice fp regulators imo.

 

[nvrenuf]

Based on my calculations, I need about 75gpm at 6psi.

I'm no mathematician but if you need 75 GPM and have a max capacity of about 40 gal (IF you have 2 big tanks) how will this ever make it out of your neighborhood? Are you sure about that calculation? Should that be GPH?

Also, according to Google (so it has to be true lol ), 3/8 fuel hose has a flow rate of 4-8 GPM.

 

[85K304SPD]

Wow a 632? How do you get one of those for the street? Sounds like an engineering marvel. I guess you would be able to drive it about 1/2 an hour at full throttle, with both tanks.
Try it out with the 3/8" fuel lines, if it runs out of gas, put bigger lines and bigger pump.
Let us know how that goes.

 

[MtBraun]

I'm no mathematician but if you need 75 GPM and have a max capacity of about 40 gal (IF you have 2 big tanks) how will this ever make it out of your neighborhood? Are you sure about that calculation? Should that be GPH?

Also, according to Google (so it has to be true lol ), 3/8 fuel hose has a flow rate of 4-8 GPM.

Sorry for the typo, should be GPH. I see all kinds of flow ratings for 3/8 so thats part of the reason for my question. I just can't seem to find a consistent number. To my knowledge the only thing that should affect flow rate is pressure. Most of the flow rates I find online do not include the pressure for that number, so perhaps that's the reason for the variability.

 

[MtBraun]

Wow a 632? How do you get one of those for the street? Sounds like an engineering marvel. I guess you would be able to drive it about 1/2 an hour at full throttle, with both tanks.
Try it out with the 3/8" fuel lines, if it runs out of gas, put bigger lines and bigger pump.
Let us know how that goes.

The pump is the easy part. Just don't want to build lines that are too small and have to replace everything. Also not sure if they stock selector valve is going to be too restrictive.

 

[Bextreme04]

The pump is the easy part. Just don't want to build lines that are too small and have to replace everything. Also not sure if they stock selector valve is going to be too restrictive.

Mass flow is determined by the smallest choke point in the system. The pressure and velocity of the fluid will vary at any given point, but the mass flow will be constant before the choke point. In this case, your choke point will be the fuel pressure regulator. GPH is a mass flow rate, pressure is immaterial to the mass flow rate.

I can show you a bunch of equations and describe to you why that is the case... but I doubt there are many people on here that want to go that in-depth.

Is this a Gen VI or aftermarket BBC that doesn't have the mechanical fuel pump provisions? Because holley definitely makes a mechanical fuel pump that would bolt up and support 110GPH flow rate. You wouldn't even need in-tank pumps or an external fuel pressure regulator... just bolt it up and off you go, with all the stock tanks, senders, fuel lines, and switching valve.

 

[MtBraun]

Mass flow is determined by the smallest choke point in the system. The pressure and velocity of the fluid will vary at any given point, but the mass flow will be constant before the choke point. In this case, your choke point will be the fuel pressure regulator. GPH is a mass flow rate, pressure is immaterial to the mass flow rate.

I can show you a bunch of equations and describe to you why that is the case... but I doubt there are many people on here that want to go that in-depth.

Is this a Gen VI or aftermarket BBC that doesn't have the mechanical fuel pump provisions? Because holley definitely makes a mechanical fuel pump that would bolt up and support 110GPH flow rate. You wouldn't even need in-tank pumps or an external fuel pressure regulator... just bolt it up and off you go, with all the stock tanks, senders, fuel lines, and switching valve.

Maybe someday on the equations, but not today, lol. This is an aftermarket 632, Dart Big M. It has mechanical fuel pump provision but was built blocked off. I would have to check, but think there is a special requirement for the cam to support a mechanical pump. Skip White told me they recommended an electric pump, so that's how I had it built. I guess the next question would be is the stock feed and return lines adequate for a mechanical fuel pump at 110gph, 6psi?

 

[85K304SPD]

It is unlikely that anybody else has ever ran this combination, a 632 in a square body, so you are pretty much on your own to find out how it is going to work and then you can let us know.

 

[Bextreme04]

It is unlikely that anybody else has ever ran this combination, a 632 in a square body, so you are pretty much on your own to find out how it is going to work and then you can let us know.

Not even close. There are quite a few of them, just search for 632 Squarebody and you'll see lots of videos.

xc_hide_links_from_guests_guests_error_hide_media

I would just put a Holley Red pump right after the switching valve and send it. If you feel like doing anything extra, put an adjustable FPR with a return line as close to the carburetor as possible and run the return line right back to the switching valve return. Holley red is rated for 97GPH @7psi.
https://www.summitracing.com/parts/...u376bXbDbz_WGQQ1kNwnR1og0iMz7fzYaAv6EEALw_wcB

Be aware that electric fuel pumps don't really like pulling uphill. Having it mounted down low on the inside of the fuel rail means it will only pull uphill during initial priming. Make sure you run a dedicated 10 AWG feed wire through a relay directly from the battery to the pump. I would use an automatic resetting circuit breaker to protect that circuit. Then run a dedicated 10AWG ground wire from the pump straight back to the battery ground. Use the ignition signal to trigger the relay on or better yet use a smart electric fuel pump controller such as this one.
https://www.revolutionelectronics.com/Products/Fuel_Pump.html
You can get them direct from the manufacturer or from amazon or ebay stores.

 

[squaredeal91]

That was a good burnout!! Damn.... but now he needs 2 grand in tires lol

 

[Matt69olds]

I’d be more concerned about the flow rate of the switching valve.

I don’t see this going well. Are you putting a pump on each tanks? Most electric pumps don’t like to pull fuel, add the restrictions of the switch valve I bet it’s worse. I’d be really surprised if a 3/8 line will be enough for that much engine.

I’d DEFINITELY put a fuel pressure gauge on the truck. Even a cheap mechanical gauge taped to the windshield would be good for a test. If the fuel system won’t maintain 4-5psi minimum while on the loud pedal, figure out why before bad things happen.

 

[MtBraun]

Not even close. There are quite a few of them, just search for 632 Squarebody and you'll see lots of videos.

xc_hide_links_from_guests_guests_error_hide_media

I would just put a Holley Red pump right after the switching valve and send it. If you feel like doing anything extra, put an adjustable FPR with a return line as close to the carburetor as possible and run the return line right back to the switching valve return. Holley red is rated for 97GPH @7psi.
https://www.summitracing.com/parts/...u376bXbDbz_WGQQ1kNwnR1og0iMz7fzYaAv6EEALw_wcB

Be aware that electric fuel pumps don't really like pulling uphill. Having it mounted down low on the inside of the fuel rail means it will only pull uphill during initial priming. Make sure you run a dedicated 10 AWG feed wire through a relay directly from the battery to the pump. I would use an automatic resetting circuit breaker to protect that circuit. Then run a dedicated 10AWG ground wire from the pump straight back to the battery ground. Use the ignition signal to trigger the relay on or better yet use a smart electric fuel pump controller such as this one.
https://www.revolutionelectronics.com/Products/Fuel_Pump.html
You can get them direct from the manufacturer or from amazon or ebay stores.

Sure wish I could find some of those guys with 632s! I'm sure they are out there but have posted to FB pages and the sort and just can't seem to find anyone with an existing setup.

 

[CountKrunk]

Any reason why you have a 632? To go fast? Race truck? Drift truck?

 

[squaredeal91]

Any reason why you have a 632? To go fast? Race truck? Drift truck?

For me it would be for burnouts and whipping sideways whenever I wanted to