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Wiring single BAP to Dual Pumps (Return style)

6K views 14 replies 6 participants last post by  markolson 
#1 ·
So I have wired many BAPs in my day but they were on returnless style systems either Pre or Post FPDM. The guy that is purchasing my car wants me to add a BAP to the dual Bosch 044s that are currently installed to the vehicle (Return style system). My question is, running a Single 40Amp BAP on this setup, is this even possible? Right now the pumps are wired by, Direct Battery power wire that splits to feed 2 relays. Each relay feeds its own pump. How would I go about wiring a Single BAP to power these 2 pumps? Or would I need a dual pump BAP like the GT 500 style? Can I wire the BAP before it splits to the 2 relays or will that be too much of a load on it?

I have been searching for a good wiring diagram but I cannot find anything. Only thing I can find is FPDM vehicles or dual BAP wiring diagrams. No single BAP to 2 pumps in a return.
 
#2 ·
The guy who really know the answer to this is Mark Olson, Dave.

My guess is the easiest place, perhaps the right place to wire the BAP is before the split to the two relays. I think the other approach would be the GT500 style dual BAP implementation.

I'll send Mark a PM and ask if he would share his thoughts.


Ed
 
#3 ·
The specs (and actual test results) I found on the internet shows that each pump will draw up to 15A. So two will draw up to 30A. But that is at 13.2V. When I was testing my 40A BAP, cranking it to the max generated about 17.5V. Increasing the current by the same ratio gets you to (17.5A/13.2A)*15A = 19.9A. Doubling that is 39.8A. There is absolutely no margin for error. KB now has a Competition model that bumps the voltage up to 20.8V max, which should draw about 23.6A per pump.

You could definitely run one 40A BAP of either model to each fuel pump and you will have plenty of margin. I could not find the current rating of the Dual BAP, but I suspect it can also handle both of your pumps. If I were doing this, I would ask Kenne Bell first. Regardless, the BAP(s) should be powered by the Direct Battery wire in front of the relays.

I also have an opinion about the Hobbes switch input. I always hated the fuel pressure spike I got when the Hobbes switch closed. It made it really hard to control the AFR just after it closed. These glitches drove me crazy when I was tuning my car. Since you are running return style, I would recommend that you just short the Hobbes switch input wires together so the BAP is on all the time. The excess fuel will flow back to the tank via the return line. The only downside of this is some heating of the fuel. The main downside to that is an increase in evaporation, putting more load on the evap system. I have never heard of warmer fuel increasing the chances of detonation, but I guess that may be possible too, but I doubt it would play a substantial role.

Unless the new owner is planning on substantially increasing the boost, I can't really see why the BAP(s) are needed, but I guess that is a different discussion.
 
#14 ·
I also have an opinion about the Hobbes switch input. I always hated the fuel pressure spike I got when the Hobbes switch closed. It made it really hard to control the AFR just after it closed. These glitches drove me crazy when I was tuning my car.
I had the same issues with a hobbs switch causing random fuel pressure spikes every time the throttle was blipped which in turn causes a minor A/F irregularity. I ended up building an electronic module that monitored my MAF curve and only when it reached a certain point before the first fuel pump was been exhausted did the 2nd fuel pump turn on. That meant I only have one point in the MAF curve where the spike occurs and I can tune around it.

It also meant no more spiking power to the second pump every time you blip the throttle. On my old engine combo I could go WOT in 1st, 2nd and half way through 3rd before the 2nd pump would turn on.
 
#4 ·
The research I found shows the pump drawing 13 amps at 12 volts. So two will pull in the area of 26 amps. The bap can the handle the two pumps. And you guess it, the bap will need to be wired in series before the two relays. The question is does he plan to turn the bap up and how high? Im running a bap in my 98 but I have it turned down. I didn't need the extra voltage, my current setup has plenty of fuel at 12v. Basically its just a amplifier to keep constant 12v on my pump.
 
#5 ·
The 98 has a 2 stage fuel system (like my 96), so your setup makes sense if you want to avoid the low pump voltage at low RPMs. However, the 99+ cars don't have a 2 stage fuel system, so it wouldn't make sense to me to put a BAP in his car and leave it at 12V. Also, you never know what the next owner will do. It is likely he will crank the BAP up and he could overload it...
 
#7 ·
We must have typing a reply at the same time Mark. If I would have seen your 15a findings, I never would have posted my 13a findings. Yours sounds more feasible. I added my bap to my setup years back because the tuner and I wasn't sure if the svt focus pump could carry my Vortech setup. To our surprise it easily did. I just left the bap hooked up and set my percentage output to 0. That was 7yrs ago and I drive every day. [emoji4]
 
#9 ·
Thanks for the info guys, very helpful. The new owner of the car, his tuner is worried that the pumps are going to be tapped out with the current combination for the new owners goals. The car will have Twin 62s with a new engine Combination. Stock Bore Alum 4.6 with Gibtecs, 9.5:1 CR, Sullivan, Custom cams etc etc. Target #s are 800-1000rwhp through a FB 4R Auto on E85. I believe the 044s can handle this on gas, but not E85 which is why the tuner recommended a BAP. So basically the only way I see this working is. Single 40 amp bap wired before the relays but cannot be turned all the way up. Or a dual BAP. He already purchased a Single 40 amp BAP which I was hoping we can get away with using.
 
#11 ·
Is there a reason why you or the new owner doesn't just want to change to twin Walbro 400's (Walbro' newer E85 rated pumps.) Seems like it would reduce the complexity of the system and be cheaper. Unless your just a fan of Bosch over Walbro.
 
#12 ·
The reason is. The car has a Glenns sleeper sumped tank. The 044s are external. To do Twin Walbro 465s, he would need a new tank/hat/lines etc.
 
#13 ·
Ahh I see, missed that part. I was thinking he had Bosch in tank 040's. If I would have paid alittle more attention I would have saw 44's.

Well that sucks...
 
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