Carburetor fuel system plumbing

[JMortensen]

I am done plumbing brakes and I'm looking at getting the fuel system ready. Engine is a 5.3, will run a BG Race Demon 650.

 

I was going to run 3/8" lines and I bought a pump back when I was going to run the L28. It's a Carter P4070 and it puts out 70 gph at 6 psi and has 1/4" NPT inlet and outlet holes. Here are my questions:

 

1. Is 3/8" fuel line big enough to support say 400 bhp? I've heard conflicting info on this one.

2. Is 6 psi that my pump puts out enough? I can't seem to find a spec on the carb. Not sure where to find that info, I did find this: http://racingarticles.com/article_racing-68.html which says "fuel pressures are typically 7-9 psi" and this: http://www.barrygrant.com/demon/default.aspx?page=29&specs=29f which doesn't specify a fuel pressure at all, surprisingly.

3. If I have a pump that puts out 6 psi, can I get away with no regulator?

4. Do the BG carbs take the same carb feed line as the 4150?

5. If I do have to put a higher pressure pump on there and run a return, can I just drill a hole in the plate on the top of the cell and install a bulkhead fitting? My cell has a fill and a vent fitting, but nothing else.

[JMortensen]

Nobody has anything for me here?

[JMortensen]

I'd even take a "put all that crap on ebay" and buy this crap instead!

[280zex]

It should be fine. I just sold a 1978 280z with a 450rwhp zz4 sbc. It has the original FI pump and feed/return lines. I set it up for 6psi running. You gona run dead head or return?? if return style then your gona need a tank breather.

My blowthru z uses the stock FI pump and return style and it works perfect..

IIRC any more than 7 psi will push past the needle and seat at least thats for holley..

Edited April 9, 2010 by 280zex

[JMortensen]

I was going to dead head it, not sure if I should dead head it or have a bypass regulator.

[JMortensen]

Took a look and my regulator is non-return and is 1.5-4 psi, perfect for the Mikunis on the old motor. So I'm looking at bypass regulators and they're more expensive than my pump! I think I'll just run the pump to the regulator to the carbs and dead head it and replace the pump more often. The last Carter pump I had was used for who knows how long, set in a box for about 5 years and then I threw it on my car and drove it daily for a couple years before it finally died.

[280zex]

Get a brass 3T fitting-female. get 3 brass nipples male thred. 2 need to be the same and close to your fuel line size, 1 needs to be .108 inch ID this is for the return line side. the other 2 are for feed from pump and feed to carb. this will give a static fuel pressure of 6psi running at the carb and gives return fuel and saves the pump. thats how I ran the fuel to the v8 and about every other holley carb setup I've ran on any vehicle!!

Edited April 9, 2010 by 280zex

[jt1]

John, the 3/8 will be fine for a 400hp car. For a long time I ran one of the internally regulated carter pumps on my car, and didn't have any problems with it. I'm not really a fan of the deadhead regulators, they seem to be quite inconsistent in my experience. A nice bypass regulator with returns gets $$$$ pretty fast, and the carter was cheap and easy. I put a gauge on it and it held 5-6 psi, and with a 3/8 line supported a little over 400whp with no problems.

 

jt

[JMortensen]

John, the 3/8 will be fine for a 400hp car. For a long time I ran one of the internally regulated carter pumps on my car, and didn't have any problems with it. I'm not really a fan of the deadhead regulators, they seem to be quite inconsistent in my experience. A nice bypass regulator with returns gets $$ pretty fast, and the carter was cheap and easy. I put a gauge on it and it held 5-6 psi, and with a 3/8 line supported a little over 400whp with no problems.

Am I reading you right? You ran the electric pump I have with no regulator and no return straight to the carbs then? Or did you run the mechanical pump? Seems like nobody uses a FPR with the mechanical pumps...

[jt1]

Yes. I went and checked, and I'm running that exact same pump, 355 sbc, 420whp, no regulator. The only trick things are I enlarged the ID of the fittings that attach to the pump, and ran a single piece of 3/8 line from the pump to the filter, so no loss thru a bunch of fittings. Clean/simple/cheap/works.

 

jt

[JMortensen]

I still have to buy hoses and fittings, and now I have two choices. The cell has a -8 outlet and that makes me think I should run the entire system in -8. I found a 1/4 NPT to -8 fitting, so even that little pump wouldn't be a problem.

 

If I go -8 I will have a SS flex line from the -8 fitting on the cell to a filter, more stainless flex to the pump inlet, aluminum line from the pump outlet to the front of the car and to a bigger fuel filter in the engine compartment and a flex line from the filter to whatever carb inlet I find that fits the BG carb. Going to wait until I get the carb to buy the inlet to make sure it is right.

 

I also have some of the parts to run the system with rubber hoses (I have some 3/8" hose and various barb fittings). If I go this way I would save probably $100, but I keep struggling with the ss flex line issue. I'd like this thing to be safe which makes me think I should go all AN and stainless flex hoses, although every other car I've ever owned or raced has had rubber hoses. I would need a -8 to 3/8" barb for the cell, then I have rubber hose and barbs for the filter and the pump, then it would be probably -8 outlet to the 1/2" aluminum, to the fuel filter, then barb again and rubber hose to the carb.

 

I know I can make this thing tech-worthy for autoxing with rubber hoses and save some cash. I'm just trying really hard not to have to redo this stuff later on, because next time I'll likely be on my back underneath the car instead of standing next to an upside down car on a rotisserie. Suggestions here?

Edited April 13, 2010 by JMortensen

[jt1]

Since this is a ground up build, IMO it would be best to do it in stainless and hard line. If you were converting an existing car, the rubber has some advantages, but in this case I say do it once and done. You will never work on the car in the future as easy as it is now.

 

Stick with -8 from the cell to the pump for sure. No reason to downsize there. I really think a -6 would work from the pump to the carb, but in the one & done theory it would be pretty easy to go -8 all the way. There would be more expense to the -8, but not a lot. If you use a fuel log to attach to the carb rather than a hard line, it makes jet changes much, much easier. The line and the log need to be compatible, so keep that in mind. I like to run the filter right before the carb, running it in suction can present some extra problems, but I've seen a lot of people run them that way without issues, so it can obviously work.

 

Let us know what you decide.

 

jt

[JMortensen]

I went ahead with push lok hose and fittings and -8 all the way up to the front. I didn't want to have to figure out the ss braided lines, and the push lok stuff is apparently pretty easy to hook up and way more than capable of handling 6 psi, plus it doesn't require clamps. I also decided to do another flexible line junction between the pump outlet and the hard line. I just wasn't sure attaching the hard line straight to the pump was a good idea. Got all the fittings and hose and clamps to do the whole thing for $125 shipped. Will post pics as it comes together.

[JMortensen]

Got all my fittings yesterday, thinking about how to mount the pump. On the stock tank I mounted the pump to the two holes in the front that are right on the seam where it is pinch welded. On the cell I don't have that luxury. I have a frame around the top of the tank, but nothing below as this cell is designed to hang from the top flange. One thought I had was to mount the prefilter and pump right off that frame, but I understand that the pump supposedly works better the lower it is. Not sure that this matters when the fitting that comes off the tank is already higher than the proposed pump mounting spot.

 

Also I currently have the cell mounted with bolts and nuts, was considering doing some/all nutserts on the frame, but not sure if that's a bad idea just in case the car flips. I know the nutserts aren't as strong, and these in particular are aluminum nutserts, but I figured I'd ask. I think it would be easier to change the pump if I didn't have to find the nut on the bottom to get the bolt out is my thought.

[bjhines]

I used 3/8"(-6AN) for everything(feed and return). I ran aluminum hardlines under the car. I have dual high pressure EFI (in tank)pumps with an Aeromotive return regulator near the carby. I figure the dual EFI pumps will supply more than enough flow rate for just about anything I could shoehorn into the engine bay. I am also set for a future EFI system on a later motor.

Edited April 20, 2010 by bjhines

[JMortensen]

I've been watching your plumbing thread. Very nice.

 

Any opinions on fuel pump height? I really think it will be OK at the cell flange level, it is lower than the outlet of the cell on top.

[bjhines]

I own a Nissan Pulsar ITC car with the fuel cell mounted low in the trunk and the pump high on the rear seat-back panel. It works fabulously, it primes easily and has a canister-filter just after the pump.

[JMortensen]

Problem number 7958. When I put the 90 degree fitting on the cell, it sticks up about 2 inches above the rear deck. I guess now I need to figure out how to seal that area off. I could put a cover over the deck and then pop up where the fitting is I guess. Or I could put a raised frame in above the deck so that the cover could be flat. Either way looks like more work than I wanted to do...

[sweetride2go]

Man Jon, if you are going to have the car on a rotisserie it would be really easy to work with in regards to running the hardlines. And the SS braided lines aren't that hard once you do a couple. Check out the "how to" on youtube for assembly.

 

As for the pump, I am also running that pump on my V8 Z with a deadhead regulator. However, I had the regulator for a different pump that didn't work out. I have run that Carter pump on another V8 with no regulator and it was fine. In hindsight, I wish I had run a return line and return regulator, they do seem to be more accurate, even though my current configuration seems to be fine.

 

I ran SS hardline under the car and only have about a foot of SS flex line on either end. I made this line from under the car, I wish I was able to put it on a rotisserie! ha

 

Here is my regulator and shortline to the carb, which is a 4150 style from Proform.

 

Cheers

Ryan~

[JMortensen]

I'm already mostly done with the push-lok and I have heard enough horror stories about ss braided that I'm not going to turn back now. I know this will be OK for tech at autox and track days, which is what I'll be doing for the foreseeable future. I think it's good for road racing too, not sure haven't bothered to look. I am having a bit of trouble with the filters and pump, just figuring out where to put everything in the car. If you line up the filters and the pump and fittings, they're longer than one side of the fuel cell. I can't put them in the front because I can't get at that side of the cell frame to drill holes, so I put the pump and filter on the driver's side of the cell. This means that my 90 heads BACKWARDS to get to a first filter, then around the corner to the pump and filter. Not really happy with the way this is turning out. I really wanted to keep the fuel lines away from the rear just in case I do decide to road race the thing, but I guess if I do that I can just redo the plumbing at that point.

 

Here's what I have so far. I'm not sold on this, so if anyone has a better idea, now is the time...

 

Pump and filter with about 1" hose in between the fittings:

 

 

Top view, filter before the pump is held on with hose clamp screwed to frame. Better way to do this?

 

 

Soft line will be clamped to frame rail and will head right through this little hole between mustache bar and frame:

 

 

It will end up on the floor here and there will be a union to attach the hard line.

 

 

One problem I'm having is this rear corner of the cell. The hose doesn't like this corner and a 90 is just a bit too short, so I think I'll have to get a 45 for this part.

 

 

So that's about it. Haven't done the hard line stuff yet, but that's going to be really easy. It's where to put all these little parts that is giving me a hard time. Suggestions on how to do it better appreciated as usual.