Looking for some advice on my EFI/Carb fuel system swap

[tokarz1]

There is and I'll try to find it.

It's basic fluid dynamics and same thing I did for the Fire Department, even though I was working with 120 psi and 4 inch an 6 inch supply lines. Concept is the same.

Basically its cross section x pipe length, then factor the flow at meters per second at the rated pressure. Zahn cup viscosity of water is about 12 to 15 seconds, viscosity of fuel is on a chart I'll have to dig up.

Quick Fuel should have the data of actual fuel consumption based on CFM per the actual engine and the RPM.

Rich is 12:1 Stoichiometric of 14:1 is theoretic goal.

So 12 pounds air per 1 pound air to 14 pounds air to 1 pound air in a cubic foot multiplied by how many cubic feet moved in that minute.

The engine is just an air pump, so find your max goal of RPM and a 454 is not normally turning 7k.

Bore x Stroke is (4.25 x 4.00) or (4.28 x 4.00) if 30 (0.030) over. Area of a circle (04.25) is 14.186 square inches and total cylinder volume is 56.744 cubic inches.

At 5500 RPM this engine is going to move (56.744 x 8) x (5500/4) = total cubic inches consumed in one minute.

449.448 x 1,375 = 618,046 cubic inch per minute. Equals 355.608 CFM.

From there .0807 lbs air x 355.608 = 28.697 lbs air and 2.391 pounds of fuel at a rich 12:1 AFR.

So 2.39 pounds per minute and 9 psi at 30 GPH is .5 gallons per minute..., so will this work??

One gallon of fuel is about 6 lbs per gallon, so this makes the requirement at or about .398 gallons per minute at 5500 RPM at a Stoichiometric of 12:1 and a little more running richer.

28 GPH = .467 gallons fuel per minute
30 GPH = .500 gallons fuel per minute
32 GPH = .533 gallons fuel per minute

Just doing this from memory, but seems to show 9 psi at 30 GPH is sufficient and this is exactly what OEM set this at for the 427 and 454 Big Block Chevy going back to when it came on the market.

Thank you for that! This is way out of my league, and I am still learning about this.

 

[tokarz1]

Not to hijack, but will those fitting fit about all barb end lines or would they nave to be simular to the way the sender is made. I'd like to try them on some of my other hard lines.

From what I have read, you cut off the nipple on the end (Red circle) and leave aprox 3/4" - 1" in front of the barb (Green arrows).

 

[pagrunt]

From what I have read, you cut off the nipple on the end (Red circle) and leave aprox 3/4" - 1" in front of the barb (Green arrows).

View attachment 231449

That's what I needed to know. Now to figure out if I want to cut my stainless lines,

 

[78Delta88]

Not sure what you have in your area, but most hardware stores will have the compression fittings designed for this.

Once you know the diameter of the line get the corresponding compression fitting. One side will be compression the other side NPT (pipe thread) and those are in brass and have the pipe nipple size you need.

I did this recently from ACE Hardware; 3/8 Compression to 1/4 NPT Female. Next piece was 1/4 NPT Male with a 3/8 pipe nipple. The nipple is barbed, so fitting over the 3/8 fuel line and secure with worm clamp worked just fine. Cost was a little over $8.00 USD, no leaks.

 

[64nailhead]

I had a 92 Crown Victoria that I swapped a 289 into. Car was originally a 4.6 with EFI, probably ran at 39psi stock. I used the aforementioned Mallory regulator (return style) to turn it down to 6 psi to run it with a carb. Worked like a champ. That is why I recommended the Vortec pump from a 96-97 truck. Pumps don't make pressure until something resists their flow.

For that to work, a couple of things have to be setup correctly. 1st, the regulator has to be able to operate at that pressure without creating any damage. And 2nd, a pump that doesn't mind running at the excess pressure. I'd guess that teh pump wouldn't ever be an issue, but a regulator could be. If it worked for you, then great!

 

[Supercharged111]

For that to work, a couple of things have to be setup correctly. 1st, the regulator has to be able to operate at that pressure without creating any damage. And 2nd, a pump that doesn't mind running at the excess pressure. I'd guess that teh pump wouldn't ever be an issue, but a regulator could be. If it worked for you, then great!

I can't see it ever being an issue for the pump, until you're in an extreme scenario like trying that with a 450 or something where the return line can't flow enough to bypass enough fuel to get the pressure down where it needs to be. Not a problem for any of the pumps suggested this far. The regulator I spec'd has 3 different springs you can install and one of them is for carb pressure ranges.

 

[Ernest]

Just use an electric fuel pump with up to 4x the pressure you inted to run at the carburetor to compensate for pressure loss through the length of lines and filter... gives you plenty of overhead with no worries.

 

[78Delta88]

The issue is..., you are getting out of the design ranges of the item.

From there your reliance on the manufacturer's safety factor is just that. Usually things work out ok, with a well made item and with normal quality control, but failure could have catastrophic results.

If you are running a pump pushing 40 to 60 psi..., don't step it down to 7.5.

Get a pump pushing 9 psi and manage the output at 7.5. This is a much safer method.

 

[Supercharged111]

The issue is..., you are getting out of the design ranges of the item.

From there your reliance on the manufacturer's safety factor is just that. Usually things work out ok, with a well made item and with normal quality control, but failure could have catastrophic results.

If you are running a pump pushing 40 to 60 psi..., don't step it down to 7.5.

Get a pump pushing 9 psi and manage the output at 7.5. This is a much safer method.

Pumps flow a given rate at a given pressure. There is no such thing as a "60psi pump". That's why I suggested finding a calculator as OP will want to fall in the 30-40gph range at his operating pressure. Simply saying that a "60psi pump" won't work is not the way to make an informed decision.

 

[78Delta88]

I understand what you saying and concur actually as someone stated before pressure builds after resistance. Actually what your looking at per viscosity and flow rates is max resistance it can take before the motor goes in to stall. Once in stall it overheats and stops working.

So taking a high flow rate unit and restricting it down and maintaining that just isn't the best way to do it.

Then you get into marketing and how things are rated so they can be sold. Holley Sniper as an example doesn't state flow rates, yet that is what the injectors need. Certain flow at a certain speed to develop enough pressure to spray into the throttle body while the engine is running. Or no vroom vroom. So what does Holley specify?? 58 PSI. If that is the case then there has to be a pump that specifies ... 58 PSI, or some verbiage that leads you to believe it would suffice, otherwise..., why would you buy it?

So I concur with what you are saying, but if OEM says it is a 9 PSI pump, and the pressure return is set from the OEM at 9 PSI, and someone asks what pump should I get??? I wouldn't suggest something rated at 39 for something only requiring 7.5.

At atmospheric 14.7 psi at sea level get a 5 gallon bucket dumped on you or get sprayed with a 3/4 inch garden hose at 120 psi... Which one gets you wetter, faster? Each have their own specific flow rates and flow characteristics.

Simple terms if your carb needs 7.5 psi from a 3/8 inch diameter supply, get a pump (9 psi) and regulator (set at 7.5) that will work for that, then go drive it and see if that works.

You might find the 9 psi pump goes flat after a certain RPM. Then try the 15 psi pump, maybe flat spot goes away. This is why I suggested the 15 psi unit. The carb is designed for a mechanical system. So an electric at 9 or 12 or 15 can't handle that???