Hey guys. When I first did my vortech install the shop told me I that they upgraded to fuel pumps to a dual Walbro 340's. I never checked since I never had a problem. Now I have installed a smaller pulley, bigger 103lb injectors and e85. At only 10psi and 671rwhp with low timing, I'm losing fuel pressure past 6k rpms. It's going from about 75+ to 50psi. Looks like I'm maxing out the pumps. Will dual 400s do the trick? Aiming for 700rwhp.

LS3 with v2si.

 

I would do dual 450's if you were having to do the work to upgrade. Kinda interesting you are already maxing them out though. I am probably almost at your power level with my car, however my car is still on twin 255's (e85 car also).

 

Ill be looking at both tomorrow, the 400 and 450. My tuner mentioned both but said the two 400's should be more then enough especially since im only running low on pressure past 6k. For me itll probably come down to physical size since im not sure how much room I have to work inside the tank and pump hat. I should see a little more then 400lph from each pump since theyre rated at 12v and my hotwire kits bumps that up.

 

I do not think you should be maxing those pumps at your power level on e85, maybe one of them is on its way out

 

wiring issue? There is no way you should be maxing out 340's on that power level with e85....

 

I wouldnt be surprised. I had to replace and repair a lot of the wiring the shop did in the fuel system. That or they installed smaller pumps. Ill find out on Sunday.

 

Anyone know if running two Walbro 400 pumps continuously i stoo much? Im not sure if e85 heats up like gasoline if the pressure is contantly high.

 

When we were suspecting the fuel pumps, I took video of the gauge. As you can see, when the pull starts it starts to lose pressure. Another concern is how much the needle is shaking. Not sure if its being caused by engine vibrations or a bad/clogged fuel filter/pressure regulator. The fpr is built into the filter in this C5. Anyway to be safe I ordered a new filter since I cant even remember the last time I changed it.

 

you arent running a return style fuel system with a boost referenced fuel pressure regulator?

 

I'm running dual 340's up to 22psi on e85 no problem. I'd look at your wiring first before going bigger pumps because you may have the same issue with larger pumps. Fwiw. I've ran dual 255 pumps up to 17psi on e85 without a drop. Your pumps should be fine providing they are healthy.

 

No, at least not yet. LS3 fuel rail with the 2002 non return system. I believe both pumps run continuously.

 

I replaced the wiring harness with a new one and have a hotwire kit from Caspers.

 

Those pumps should be lots I'm using twin 255 with 18+ psi. I had a similar issue when we first started tunning my car it would drop fuel pressure around 5700 we looked at the volts and they were dropping at that rpm you could see on hp tuners exactly were the volts would come down in result fuel pumps were not getting proper volts to run efficient I also have the hot wire kit. So I did the big three wire upgrade and after that volts held stronger threw out the pull and solved issue. Also not sure what guage your using but a liquid filled one will solve the erratic needle shake

 

Walbro doesn't make a 340lph fuel pump, the gs340 fuel pump is a 255lph which often confuses people. Have you tried lowering the base pressure? They really start to fall on their face at higher pressures. Even at 3 bar fuel pressure the idc will be low at that hp level.

 

Sent you a pm.

 

I think you're right. They may have done a twin aeromotive setup. I just picked up the two walbro 400's. I can probably tune around it but I'mddefinitely putting together a return style setup with a boost referenced fpr and -8an/-6an lines. I'll find out for sure what'sIin their when I pull the pumps out this weekend

 

You need a return fuel system and boost reference regulator along with a Hobbs for second pump. You may have burned those pumps up spinning them at 70 lbs pressure. Oh my. The 340 pumps don't like to spin hard. Lower that pressure to 43-45 lbs and increase injector size if needed. Use one pump continuously and trigger the second pump when needed.

 

I thought that with a return style system you can run both pumps continuously. That's the advantage, not relying on a secondary swith/power source.

 

dont worry about running them both. Atleast i never did anyway.

Im not a fan of "Hobbs" switches. I had two of them fail and leave my pump running. So i said screw it, and ran them both full time.

Yes, you need a return style system. People say not to run them both because of heating the fuel. I would drive mine on long trips, 2-3 hours and never had any issue. But to each his own.

If running an aftermarket ECU, then by all means, use it to trigger the secondary pump.

 

Even on a return system I wouldn't run both - the reason provided in the prior post and it's simply not necessary.