You don't want to run both pumps at the same time at idle or low rpm with the stock fuel lines because the fuel pressure will begin to rise uncontrollably. I think somewhere down the road I may replace my stock fuel lines. That braided stainless steel line looks really good and lasts forever.

 

Ya I addressed that in my last post. I'm not really sure where the safe point would be (Guess its a factor of BSFC)

 

Its a two position double pole double throw switch rated for 5amps at 120VAC. I got mine at radio shack but I think Most of the Auto parts stores should have them. It has two inputs and 4 outputs. Two jumper wires across the outputs completes the circuit like atljar drew.

You could get a three position with center off for a fuel pump cutoff for antitheft purposes.

 

Question about the wiring for the second pump. What about the ground wire for it?? Would it be easier to wire the ground into the same ground in-tank where the first pump is??? Or would it make more sense to take the wire through the top of the bucket and ground it elsewhere??

 

Thinking along those lines, why go to the larger fittings if any intermediate fitting or hose is smaller than the 3/8" fittings? The smallest diameter in the 'chain' is the weakest link. In the pic in the original post, I see the post 'Y' block fittings and hose as areas to address B4 going larger at the pumps. The APE flex hose is of OEM size, correct? This hose is now required to flow fuel from two pumps now. I see that (and fittings) as the weak link.

 

What size -AN hose would fit over the pump nipples?

-B

 

another thought on this: I saw the use of an MSD activated RPM switch mentioned in this thread instead of the hobbs. Word of caution: I researched this last night and can't seem to find an MSD RPM switch rated for over 1.5 amps of draw, and IIRC those walbro pumps draw WELL over that.

 

I see what your saying. The only reason I even mentioned it was because there are quite a few people that have begun running larger volume line to the fuel rails to support the fueling requirements for there particular setup.

If that's the route that you eventually plan to go then it may just be easier to do it all at once and get it over with.
Again it appears that once my mind starts cranking my typing just can't keep up and I get the details out before the explaination.

 

I believe its the guy running the F1 and HUGE ATI bypass valve. I believe he mentioned that he uses the MSD RPM switch to activate a relay that turns on the 2nd pump.

-B

 

Durrrrr....durrrr....durrrrrrrrr........Guess I could have figured that out huh??????? Told you all I suck with electrical stuff. So how would I go about wiring that in if I were to go that way?

 

No the weakest link is the inside diameter of the steel lines. The flex hose fits over the outside diameter of the steel lines. I used a micrometer to find the weakest links. I don't agree with bigger is better in this case.

 

OK, but this doesn't change the mindset any. I'm saying the 'accordian' flex tubing used is of OEM size, correct? It was originally used with one pump. We now have two pumps. That's twice the volume capability. How much larger does that tube need to be to flow twice the volume? OK, now we approach the steel lines. So they are at LEAST as restrictive as the flex tubing inside the tank. Same scenario. We add an additional pump inside the tank, and attempt to push the extra volume thru the same size tubing. Not only do we need to find a larger flex tubing, we also need to install a larger steel tube that exits the tank. If we do not address both of these issues, adding the extra pump is little more than showmanship.

Bigger is not better? It is not the idea of bigger, it is the issue of providing the volume necessary in the transport network to support the volume of the extra pump. It is not about bigger being better, it is about addressing the weak links that have now surfaced with the addition of the extra pump.

 

Any one know Geoff Chadwick?

He built this



Notice the bulkhead fitting and the larger feed lines.

 

There are guys on this message board that are making close to 1000HP with stock lines, filter, regulater and a dual walbro. If you go with a bulkhead fitting out the top of tank then you must replace all the stock lines, get a new regulater, modify your fuel rails, and get a new fuel filter. If you don't do all these things the bigger fitting out the top of the tank is just for show. I think it looks really nice and I may go that route later. I didn't want to replace and modify my fuel rails and regulator.

If you get a chance look at the inside diameter of the outlet of a walbro 255 pump. It is tiny. It is approx. 1/8" ID. It also has a check valve that further restricts flow. Yet this small opening is capable of flowing 255lph. The inside diameter of the flex hose is 5/16." Inside diameter of the steel lines is 1/4" in some places. Believe it or not the plastic stock fuel lines are the least restrictive part of the system.. With the pressures that these pumps operate at they don't need -10 lines to move enough fuel. -10 lines in my opinion are for carburetors that operate at a much lower pressure.

 

that uis a good question but can be answered fairly simply... with the walbro pumps, as pressure increases, volume output decreases. so if you require higher pressure, the pump will not perform as advertised.. it varies inversly. by adding the second pump you are increasing the volume of fuel that can be delivered at elevated pressures. stock lines can support a good deal more then most people give them credit for. but if you are doing twin pumps and feel the need to upgrade fuel lines.. a cost effective recommendation is to go the hard line route. hard aluminum fuel tubing is much less expensive then braided stainless steel and actually will out flow the same size braided rubber lines due to a lower drag coefficient on the interior wall of the tubing. it will also act more like a radiator cooling the fuel that the pump is heating on the way to the engine compartment. the tradeoff for price is it will require some finesse installing it.. In retrospect, I would have gone hardlines on my fuel system and saved a couple hundred bucks in the process.. don't be fooled.. the pumps are the cheapest part of building a fuel system.. start adding up all the -AN fittings and braided line and regulator etc etc.. and you can be $1000+ real quick. but if you wanna make the power... you gotta pay the piper.. its just the way it is!

Chris