B6 1.8T fueling system - limits, upgrades

[vtraudt]

How far an the returnless fuel system of the B6 1.8T be pusheded?
What HP levels have been reached/documented? Pump gas and E85?

What are the bottlenecks?

What mods are required to run support 500 cHP on E85?

[EuroxS4]

500chp is the limit on the stock fuel rail. Your gonna need a bigger pump and injectors especially for e85. Tack on another 20-30% more for e85 in comparison to pump fuel. Just about everyone converts to a fuel system with a return line and converts to rising rate fpr. Its the best way to do it if you ask me.

[vtraudt]

500chp is the limit on the stock fuel rail. Your gonna need a bigger pump and injectors especially for e85. Tack on another 20-30% more for e85 in comparison to pump fuel. Just about everyone converts to a fuel system with a return line and converts to rising rate fpr. Its the best way to do it if you ask me.

And just run the return line back into the existing line (at the fuel filter0?

[vtraudt]

Side question: had a B5 18T with B6 AMB engine. Put the B5 fuel rail back on, but noticed the injectors (initially use the stock with stock tune; later 550 with respective tune) were creating a vacuum leak.
Possible that the B5 rail on the B6 intake is creating a mismatch?

[A4SoftWalker]

I have to ponder this one a bit... fuel rail creating a vacuum leak?
Not a fuel leak?
Did you mean the intake manifold?

If you can share some photos. Sounds like interesting stuff.

[vtraudt]

I have to ponder this one a bit... fuel rail creating a vacuum leak?
Not a fuel leak?
Did you mean the intake manifold?

If you can share some photos. Sounds like interesting stuff.

B5 rail on B6 intake mismatch.
Angle/position seemed a bit off.
Spraying the injector seat of the intake to confirm vacuum leak.
I bent the rail brackets and elongated the 2 mounting holes. That allowed the injectors to be more perpendicular to the intake and more centered in the intake injector hole/seat.

[vtraudt]

Who is running a larger pump (which?) on a stock B6 fuel system (just larger injectors for example)?

[Gin+]

This calc might help.

https://fuelinjectorclinic.com/flow-calculator

Keep in mind the stock return less system runs at 4 bar (58 PSI). Once you start messing with the numbers you can see how a rising rate FPR benefits fuel delivery.

[vtraudt]

This calc might help.

https://fuelinjectorclinic.com/flow-calculator

Keep in mind the stock return less system runs at 4 bar (58 PSI). Once you start messing with the numbers you can see how a rising rate FPR benefits fuel delivery.

Will replacing the stock integrated filter/FPR with a 'normal' filter, AFPR and return fuel rail (return going to 'stock' return connection) allow running larger fuel pump? That would be assuming that the stock filter/fpr is creating the flow restriction, not the stock 'return' system.

[EuroxS4]

Side question: had a B5 18T with B6 AMB engine. Put the B5 fuel rail back on, but noticed the injectors (initially use the stock with stock tune; later 550 with respective tune) were creating a vacuum leak.
Possible that the B5 rail on the B6 intake is creating a mismatch?

Possible maybe. However injectors body sizes that fit into the manifold are the same IIRC. Its pretty much a standard. The only thing i would say could cause a leak is if they were at an extreme angle. However I would say most likely cause would be cracked injector cups in the manifold.

[vtraudt]

The only thing i would say could cause a leak is if they were at an extreme angle.

No issues after a) using the 'fatter' Audi O rings (compared to the lower ones that come with the Bosch) b) bent the B5 rail 'feet' (mounting bracket) c) elongating the mounting holes in the B5 rail 'feet'.

[PSI NRG]

I just ditched the returnless cause at 28psi on my GTX2867 Gen2 I was getting lean conditions. That’s with 1000cc injectors and an AEM 340lph pump. Problem is the static fuel pressure. Once you start turning the boost up your pressure drops and the only way to get more fuel is keep the injectors open longer. My injectors were spraying at 18ms at one point which could drain the rail due to not enough volume. So I went with -6an feed and return to a fuelab adjustable regulator and 034 rail, left everything from the filter back stock. Capped the vent line on the passenger fuel tank hat as well as deleted evap. Should have plenty of fuel up to 500whp on race fuel.

Image1619185182.634821.jpg


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[vtraudt]

So I went with -6an feed and return to a fuelab adjustable regulator and 034 rail, left everything from the filter back stock. Capped the vent line on the passenger fuel tank hat as well as deleted evap. Should have plenty of fuel up to 500whp on race fuel.

Excellent, thank you. Even so we were not running out of fuel with the Walbro 340 on stock B6 returnless, the HIGH fuel pressue at idle (99% of the fuel would need to be forced through the filter to tank return system) and FALLING pressure (less fuel returned back to tank, more fuel used by injectors) was NOT what we wanted to deal with.

The AEM 340 seems to be pumping a lot less fuel at idle so you did not experience the very high fuel pressure at idle? Is someone running the Walbro 450 with a return system into the "filter back to tank" in stock shape?

Location of "vent line on passenger fuel tank"?

But at least I know that the combination 340 with stock 'filter back' works.

[PSI NRG]

I never experienced any high fuel pressure issues at idle. I believe this is mainly because I’m using an adjustable FPR. The OEM style regulators don’t like any bit of back pressure or it gives you high fuel pressure at idle. So if I were you I would spend the extra money on an adjustable FPR. Plus you have more adjustability. I dropped my base fuel pressure to 3.5 bar. Which will over all be less stress on the pump on higher boost. If I need more fuel I can always bump it up but setting the base lower can keep a pump within an acceptable working range.

As far as the vent line there’s the feed that comes out of the hat from the fuel pump and then there’s an additional nipple that has a skinny black hose attached to it. That’s a vent. So I just capped it w an OEM quick connect cap.


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[vtraudt]

I never experienced any high fuel pressure issues at idle. I believe this is mainly because I’m using an adjustable FPR. The OEM style regulators don’t like any bit of back pressure or it gives you high fuel pressure at idle. So if I were you I would spend the extra money on an adjustable FPR. Plus you have more adjustability. I dropped my base fuel pressure to 3.5 bar. Which will over all be less stress on the pump on higher boost. If I need more fuel I can always bump it up but setting the base lower can keep a pump within an acceptable working range.

As far as the vent line there’s the feed that comes out of the hat from the fuel pump and then there’s an additional nipple that has a skinny black hose attached to it. That’s a vent. So I just capped it w an OEM quick connect cap.


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THanks. So upgraded fuel pump (AEM 340, Walbro 450 may still be put out too much flow for the stock return to handle?), return style fuel rail, AFPR, 6 AN return line, connect to existing return (how? what connectors?) line , cap vent (at the hat).

[PSI NRG]

So it seems when you use stock lines and an OEM style FPR the OEM return set up can’t keep up and causes high fuel pressure.

If you go w -6an feed and return with an adjustable FPR it does just fine. To connect to the OEM return you need EFI to AN fittings. This allows you to push a barb in like OEM. You’ll need a male on the return and a female on the feed. IMG_9990.jpg


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