CO_VR4

iTrader: (83)

The FPR pressure in theory rises with boost on a 1:1 ratio (until confined by the limitations of the system). Your fuel PRESSURE may rise, but your fuel VOLUME is still limited by the pump output, and by the size of the lines and fuel rail. Fuel pumps of the kind we use provide much less volume as the pressure demand rises, and so you can see increased fuel pressure on your gauge, but may have exceeded the VOLUME that the pump can supply, and then you run lean anyway. For example, the fuel curve for a "normal" Walbro 255 goes to -0- at 90PSI! You thus are looking for a pump that flows the volume of fuel that your motor needs AT THE BOOST LEVELS you are running as a maximum, and then making sure the rest of your system is large enough to flow that amount, so the pump does not have additional restrictions like a too small feed or return line, or fuel rail bore limitations.

With a larger turbo, this becomes extremely important to consider, as the AFPR only responds to increases in boost pressure by increasing fuel pressure. Base fuel pressure (in PSI) + boost pressure (in PSI) should = increased fuel pressure by the FPR or AFPR (in PSI), but VOLUME + PRESSURE are both critical.

CO_VR4

iTrader: (83)

Curt,

Did you have the full AMS fuel system as well, with the higher volume fuel and return line, the larger bore rail, and the AFPR?

CBRE

iTrader: (77)

Yes to all.

CO_VR4

iTrader: (83)

The complete fuel system on Curt's car is a good example of what I was saying -- his twin pumps have the pressure to provide the higher volume, and the larger lines and rail allow that volume to reach the injectors without a bottleneck. Without both, you can have large lines but not enough pressure from the pump, or you can have lots of pressure from the (twin) pumps, but not enough bore size in the lines and rail to get the volume to the injectors. Either can cause a lean condition, but the latter can cause a lean condition when you think you're fine because your fuel pressure gauge is showing the 1:1 fuel pressure rise that you expect.

ItalianEvo

Exactly CO VR4,

many people don't understand that you NEED a certain lph volume @ base fuel pressure+boost pressure.

To increase the flow of my 850 cc/min, I'm now running a base fuel pressure of 51 psi.
Given that I could run + 29 psi of boost, I have to consider my fuel pump flow at 51+29 = 80 psi.

And a "normal" Walbro 342 HP @ 80 psi is around 190 lph ?

Definitely not enough for BIG HP numbers...

kjewer1

iTrader: (4)

Though most of what you are saying is accurate, one point is not entirely correct. You can not seperate flow and pressure like that Pressure, like boost, is simply a result of flow and restriction. Restriction is adjusted by the regulator. If flow drops off, so does pressure. If pressure stays up, flow is suffucient. Any additional flow is simply returned to the tank as waste. Flow dropping to 0 at 90 psi is an extreme example, that is the pressure the bypass valve should be open at. The rest of what is said about making sure that flow is adequate for the volume of fuel being consumed at the target fuel rail pressure is correct, of course, and is something that is too often overlooked.

Regardless of what rail pressure is, pressure across the injector will still be base pressure, since the additional pressure added by the 1:1 regulator is offset by the boost in the manifold. That is after all the entire point of the 1:1 FPR 43 psi base plus 40 psi boost equals 73 psi rail pressure, but still 43 psi across the injector.

BoostN

iTrader: (3)

I swapped my regular walbro 255 that I had in my WRX, started to lean out @ 29psi with a GT35R. With the BR modified, I can go 34psi before going lean.
This is using a utec for EM. Thats just some non technical real world data.
This is also with stock FPR and lines using Perrin fuel rails and PE 850 injectors

InfamousDX

Thanks for the info. that helps a lot actually. Did you get tuned by Clark Turner?

I'll be running a 35r, hydra, 1000cc, and aeromotive adj. FPR.

BoostN

iTrader: (3)

Yes, he tuned it. We are going with the speed density as soon as he comes out next or during Sema.
Peace

Paul Nelson

iTrader: (1)

according to walbro there pump can not be modified. the only thing i could find different is the output part of the pump is much bigger but the internals are the same...
Walbro 255 Fuel Pump only # GSS-342
http://mzmperformance.com/Merchant2/...de=walbrogssfp

Smogrunner

iTrader: (5)

This is turning into a great thread. I don't blame Buschur for not coming in and explaining exactly what makes his Walbro flow more. That information to all would take money out of his pocket. Although it isn't intellectual property per se, he deserves to make his profits by bringing a useful product to market. Soon enough, other folks will figure out what he is doing to the pumps and start doing it themselves.

sparky

iTrader: (1)

If the electrical motor in the standard 342 and the Buschur pump are the same, then the difference could be in the pressure relief spring. Either a stronger spring in the Buschur unit or a shimmed 342 spring allowing the pump to deliver more fuel above the 70#(?) relief pressure of the 342 pump. The drawback to a shimmed spring is an increase in operating temps for the pump motor which theoretically can reduce pump motor longevity.

Paul Nelson

iTrader: (1)

When i contacted Walbro and talked to there engineer they said that the pump could not be modified because of the way its made...

sparky

iTrader: (1)

On the Buick forums this issue has been tossed around with regard to a modified Walbro 340SS pump marketed by Red Armstrong at QuadAir Engineering. Red's XP+ pump is a modded 340SS unit, which I think has the same pump motor as the 342 pump we use in our Evos. The 340, 341, and 342 pumps have an improved, more efficient, higher volume motor than the older Walbro 307 pumps.

Anyhow, Red Armstrong gets his XP+ pump to deliver more fuel at a higher pressure by tinkering with the pressure relief spring. Apparently he just jams a piece of 12 Ga. wire into the spring. It works, as his modded 340 pump is good well into and above the 600 HP range on Buicks.

I assume, though I am probably mistaken in so doing, that contrary to what Walbro engineers admit publicly, if Red Armstrong can modify a Walbro 340SS pump to deliver more fuel at higher pressure, then someone can just as easily modify a Walbro 342.

Paul Nelson

iTrader: (1)

lol im sure it can be done
walbro tech went nuts on me for even thinking or saying any to the fact of messing with there pumps but thats to be expected