Conflicting fuel pump info? 255 in a GTR

[Pldovr]

So I just picked up a R32 GTR. Previous owner ran out of money after grenading the last motor. He had a new motor built, and we are picking that up tomorrow from engine shop in Calgary. Wiseco pistons, Manley rods, stock crank, ported head, cams etc. S366 turbo.

It has a Walboro 255 pump, and several friends are telling me this pump is not enough for the 500 or 550 rwhp that I plan on hopefully making.

What have you made with your Walboro 255 before pressure was dropping off?

[Turboner]

charts are available from Walbro, Find you high boost psi + base fuel pressure (ie 55fuel +22boost=77psi fuel pressure on boost) find the pump flow rate at 77 psi. then find how much your injectors will flow max. (ie 600cc x 6)

I may of missed something but its basically how i calculated what pump to get myself

http://www.full-race.com/store/fuel-systems/fuel-pumps/walbro-400lph.html

bought this one and did 540 hp (dynapack) with 600 cc tomei injectors @ 22 psi boost

no pressure lost up to 8000 rpm

[Pldovr]

charts are available from Walbro, Find you high boost psi + base fuel pressure (ie 55fuel +22boost=77psi fuel pressure on boost) find the pump flow rate at 77 psi. then find how much your injectors will flow max. (ie 600cc x 6)

I may of missed something but its basically how i calculated what pump to get myself

http://www.full-race.com/store/fuel-systems/fuel-pumps/walbro-400lph.html

bought this one and did 540 hp (dynapack) with 600 cc tomei injectors @ 22 psi boost

no pressure lost up to 8000 rpm

Thanks. That gets you in the ballpark, but it's very generous it seems to me. There's pressure drop from the pump to the rail. Theres Voltage drop from the fuse box to the pump etc.

I talked to our V8 tuner yesterday, and he said that they just make it to 500hp at only about 55 psi, so I think I will upgrade it to either a 340 or like your 400. It's easy to do at this point.

[MarusGTR]

I get where you're going at with the 22psi over 55psi rail but wouldn't the regulator see that 22psi surge way before the pump (and expuge it appropriately through the return line)?. In theoretical terms you should be looking for the dynamic pressure losses in the fuel line expected from 100% injector duty at full throttle and then add the 55psi static of the rail. This will be the pressure head seen by the pump. What you want to be looking for is a drop in flowrate -and- pressure because the pump can't supply enough energy to the flow. Being positive displacement both are dictated by the electrical power.

The layman can probably just calculate the dynamic pressure losses with the line length, diameter, peak flow rate and Moody Chart correlations.

PS: I may be talking out of my ass as I have no concrete experience with fuel systems.

[Pldovr]

OK, found our new 'Import' tuner based on the recommendation of the engine builder, and it was a relief, as he is also a long established V8 tuner, I just didn't know he did Imports.

Anyway, spoke to him, and he said a rough rule of thumb is 255 to just under 400 rwhp, 340 to just about 500 rwhp, and a 400 to almost 600 rwhp, on his dyno. As boost goes up, the Bosch 044 or the new AEM copy of it shines, as it does not have the high pressure fall off like these others.

For more serious builds, he mentioned a place out I think Ontario that sells the Veyron pump for a decent deal.

Anyway, I dropped in a 400lph Walboro.

[Pldovr]

I get where you're going at with the 22psi over 55psi rail but wouldn't the regulator see that 22psi surge way before the pump (and expuge it appropriately through the return line)?. In theoretical terms you should be looking for the dynamic pressure losses in the fuel line expected from 100% injector duty at full throttle and then add the 55psi static of the rail. This will be the pressure head seen by the pump. What you want to be looking for is a drop in flowrate -and- pressure because the pump can't supply enough energy to the flow. Being positive displacement both are dictated by the electrical power.

The layman can probably just calculate the dynamic pressure losses with the line length, diameter, peak flow rate and Moody Chart correlations.

PS: I may be talking out of my ass as I have no concrete experience with fuel systems.

I think you are over complicating.

What the pump sees for pressure will be what you see at the regulator, plus any restriction between pump and regulator, such as lines, filter, fittings.

So if the base is 50, and the boost is 22, your regulator will raise fuel pressure to 72, and that is what a regulator mounted gauge will read. Then, you will have another roughly 7 to 10 psi from the lines, so the pump will actually be working against about 82psi of pressure.

To test our fuel system on our last Chevelle, we simply idled the car, set fuel pressure to max we would see (58psi in that case) disconnected the return line, and measured fuel volume that Came out in 1 minute.

[MarusGTR]

I think you are over complicating.

What the pump sees for pressure will be what you see at the regulator, plus any restriction between pump and regulator, such as lines, filter, fittings.

So if the base is 50, and the boost is 22, your regulator will raise fuel pressure to 72, and that is what a regulator mounted gauge will read. Then, you will have another roughly 7 to 10 psi from the lines, so the pump will actually be working against about 82psi of pressure.

I have to disagree on one part: the regulator will adjust the pressure according to valve spring rate (and possibly change this spring rate with vaccum, for example, like in the RB26). Rail pressure will always be at regulator pressure. If the spring rate is a fixed value for 50psi in the rail (static), you could put 100psi boost in the engine, it -should- still be 50psi static in the rail. Problem is the flow rate through the internals of the regulator.

For example, my GTR was running 10psi over nominal pressure in the rail because I changed the pump and not the regulator. Its internals were too small (or narrow) to bleed the increased volume of fuel that was now required to reduce the pressure of the rail back to nominal. A NISMO regulator fixed this.

To test our fuel system on our last Chevelle, we simply idled the car, set fuel pressure to max we would see (58psi in that case) disconnected the return line, and measured fuel volume that Came out in 1 minute.

This is actually pretty smart if you want to see how much flowrate you can get out of your pump at a given pressure. Pretty much make your own pressure vs. flowrate chart.

But again I'm speaking out of a technical standpoint, but I think the logic is solid.

[Pldovr]

Most cars run a pressure compensated fuel pressure regulator. If base pressure is set at 50 psi, and the car is crusing at 20" vacuum, the fuel pressure in the rail will be 40 psi. If the car is making 20 psi boost, the pressure in the rail will be 70 psi. Thats how it works.

Now, some cars, like our LS powered Chevelle have a fixed pressure of 58psi, and there is no provision for a vacuum/boost reference, so in that case, pressure in the rail is constant.

But no one generally sets ip a GTR without a boost referenced regulator.

If that is not where you are getting hung up, perhaps you are confusing rail pressure, with delta pressure across the injector (the whole reasoning for pressure referenced regulators), but that has nothing to do with what the pump "sees". The pump sees what the gauge sees (plus line losses to the regulator).

[MarusGTR]

But no one generally sets ip a GTR without a boost referenced regulator.

Guess I'm special.

If that is not where you are getting hung up, perhaps you are confusing rail pressure, with delta pressure across the injector (the whole reasoning for pressure referenced regulators), but that has nothing to do with what the pump "sees". The pump sees what the gauge sees (plus line losses to the regulator).

I doubt I'm confusing anything if the last sentence was the point I was making since the beginning.

Edit: However, you are right that I incorrectly approached the problem. If you increase boost over OEM you'll have to appropriately increase OEM rail pressure through an adjustment of the regulator to maintain injector flowrate and spray quality (if the same injector is used). For some reason, I was under the assumption that the regulator in your application would be unadjustable. I'm mentally exhausted from work.

[Turboner]

Bench racing is stong with this one.
Racetronix.com you can find the veyron pump. Warning: they sell in usd $

[Dragon Humper]

Bench racing is stong with this one.

Now that is funny sh1t right there.

FWIW...twin hotwired stock pumps feed 650whp with no issues.



Jon.

[curtisgoodman]

nismo intank pump stock lines and rail... aeromotive fpr and 680cc injectors, 500whp