i figured i'd post in here since there are probably more people in this section making over 300whp than in the FC section... but how much power can a walbro 255 fuel pump support? 350whp?400whp?500whp?

 

mine is handling over 300 whp just fine

 

the reason i'm asking... i have two 550cc injectors and two 1000cc secondary injectors, a walbro fuel pump, all -6 lines, rx7store secondary fuel rail, and an aeromotive FPR/gauge.

i've been running about 35-40psi base pressure, rising 1:1 and realized it wasnt enough fuel to support my goals here (verified with my wideband) and was trying to lean out uptop. so i raised the fuel pressure up to about 50psi (a 10-15psi increase from what it was) and my AFR's didnt change at all in boost. i'm thinking possibly my walbro could be not keeping up with the added pressure.

 

crappy lines?

 

definitely not crappy lines...

 

That question cannot be answered accurately with a HP figure. The pump can flow a certain amount at a certain pressure and voltage. You can make some assumptions and give a HP rating, but the assumptions won't be quite right for your car, so it doesn't make sense to guess if you are near the limit. The fact that you raised the base pressure and the mixture didn't change under load suggests that you are already over the limit.

Turning on your headlights and defroster could change your mixture; not a good situation. You want the FPR to be in control of the pressure, no matter what electrical load is present. Pump inadequacy manifests as lower than expected pressure at the power peak (full boost, highest injector duty cycle).

As a simple improvement, you could re-wire the pump with thick wires. It is very common for the voltage to drop by a few volts under maximum load. Better wires can make a noticable difference in fuel pump performance.

-Max

 

Here's some really good info about diffrent fuel setups!

http://www.maxcooper.com/rx7/how-to/...tem/index.html



-Alex

 

 

or get a boost-a-pump, look at the walbro numbers highlighted in yellow (this is from a mustang fuel system article)

 

obviously not as much as you're trying to make

Seriously, I dont think you will have a problem solely because of the pump. I know lots of fd guys running single turbos on a single walbro.

 

I would think more than the injectors you have can deal with. The stock unit can handle 325 rwhp not that I would trust it for long. You seem to have something else going on.

 

Agree.. Constant voltage plays an important factor...

 

ive maxed mine out at 350rwhp with base pressure at 40 with 4x720cc injectors

 

Here's some more pump test data, including the Walbro:
http://www.stealth316.com/2-fuelpumpguide.htm

-Max

 

are you sure you werent maxing out the injectors? 350whp sounds about like the limit for 4 720's at reasonable duty...

anybody else making more than 350whp with a walbro?

 

ok i checked out alot of that link and it seems that they just have the "walbro 255 High output" 255 and "low output 190"

"The Walbro GSS307, GSS315, and GSS317 are 255 lph models. The Walbro GSS340, GSS341, and GSS342 are 255 lph high-pressure models. The Walbro GSS341 model (also called the 255 lph HP)"

so i'm guessing i just have either the The Walbro GSS307, GSS315, and GSS317 are 255 lph models, but i cant decipher all those graphs to decide if its going to keep up with 2 1680cc secondary injectors and 2 550 primary injectors at 50psi...

 

Could be... If my math is good, at 100% duty cycle

4x720 = 2880cc/min = 2.88L/min ~ 173 LPH ~ 46 GPH

at 85% duty cycle, ~ 39 GPH

to max out the walbro at 39 GPH at 12V takes about 83psi, if you take 40psi base pressure plus 10psi pressure loss at the fuel lines = 50psi, at a 1:1 rising rate, you have to run over 33psi of boost...

again, at 100% duty,

2x550 = 1100
2x1680 = 3360

total = 4460 cc/min = 4.46 L/min ~ 268 LPH ~ 71 GPH

at 85% duty, ~ 60 GPH

it looks like the Walbro won't be able to support maximum duty cycles on these injectors at 12V, you'll need to give it higher volts.

How much boost is needed to achieve these high duty cycles anyway?

what is the typical duty cycle for this injector setup at different boost levels?

THE ABOVE IS AN OVERLY SIMPLISTIC CALCULATION BASED ON MY VERY LIMITED KNOWLEDGE OF HOW FUEL SYSTEMS WORK. DIFFERENT BASE PRESSURES WILL YIELD DIFFERENT INJECTOR FLOW. DO NOT USE THE ABOVE CALCULATIONS TO DETERMINE YOUR FUEL SYSTEM REQUIREMENTS, ASK AN EXPERT FOR THAT. I ASSUME NO RESPONSIBILITY SHOULD YOU CHOOSE TO IGNORE THIS DISCLAIMER.

 

well, i'll be running 40psi + 10-15psi for the 1:1 so the math should work out for my situation...

i'd say at 15psi boost, the duty for 2x550's and 2x1680's would be around 65% my turbo wont support enough boost to get the injectors up to 85%, let alone 100%

so anyways, 40+15, 55psi total fuel line pressure, ~65% injector duty with the power (350whp) that the turbo can push. it looks like the pump will be ok with the injectors at 65% duty based on what you posted above.. great news

 

Don't forget fuel line pressure loss from the pump, through the lines, filter, etc. before it gets to the rail. It's around 10~15psi from what I've read.

65% duty with the 2x550 and 2x1680 injectors is ~ 46 GPH

at 40 base pressure + 10 pressure loss + 15 psi boost = 65 psi

looking at the graph, at 12V and 65 psi the Walbro flows just shy of 50 GPH

If I was you, I'd consider rewiring the pump so it gets full 13.5 Volts to have a bigger safety buffer as it will flow 10 GPH more at 65 psi with the extra juice.

If you plan on higher boost, I'd consider the Kenne Bell Boost-a-pump as it stabilizes voltage and can boost it as high as 17V with a boost sensor. The test they did showed the Walbro flowing about 60 GPH at 80 psi at 17V, which is 85% duty on 2x550 and 2x1680 injectors at 25~30psi boost with 40psi base pressure. Also a dual Walbro setup at 13.5 V would be good. It all depends on the injector duty vs boost pressure that your turbo will give you.

and again:

THE ABOVE IS AN OVERLY SIMPLISTIC CALCULATION BASED ON MY VERY LIMITED KNOWLEDGE OF HOW FUEL SYSTEMS WORK. DIFFERENT BASE PRESSURES AND INJECTOR SIZES WILL YIELD DIFFERENT INJECTOR FLOW. DO NOT USE THE ABOVE CALCULATIONS TO DETERMINE YOUR FUEL SYSTEM REQUIREMENTS, ASK AN EXPERT FOR THAT. I ASSUME NO RESPONSIBILITY SHOULD YOU CHOOSE TO IGNORE THIS DISCLAIMER.

 

sweet. thanks for the input

 

I've got a single walbro pump and I'm at 385 rwhp. I'm showing 89% on my injectors at 15psi of boost. So far so good! I've got 550's up front and 1300's for the secondary's...

 

found a great fuel calculator here:
http://www.maxcooper.com/rx7/how-to/...tem/calcs.html

it even calculates fuel pump requirements

 

FC 13b-re , 2ndry bridge , t51s , e6k , 550pri , 1600sec , stock fuel rail , sard fuel regulator , single walbro , stock fuel line and rail , boost around 0.9bar = 415whp on dynojet ,

fuel pressure still strong ,