I keep seeing tantalising little references to 4 bar FPR here, and on other 1.8T related sites.

I've done a little Google searching, and found it's a reference to fuel injector pressure (4 bar = 4 atmospleres, or just a little below 60psi). Sounds like it's not far from diesel injector pressures.

I'm not contemplating any mods (apart from a Jabba remap), but I'm still curious.

How does increasing injector pressure improve performance? What's involved?

Like I said, just curious...

It doesn't improve performance on its own. However it can increase the potential for performance. Explanation:

Stock injectors flow a maximum of 270ml at 3 bar of fuel pressure

At 4 bar of fuel pressure, the following calculates how much they would flow:

(4bar/3bar)^.5 * 270ml = 312ml or 15% more than stock.

The same increase in power would be:

235hp (max hp with stock fuel pressure) * 1.155=

271hp (max hp with 4 bar FPR, stock injectors)

However to get the 271 hp you need a turbo that can flow that much air to remain with the same air to fuel ratio. To bump up the turbo by the right amount, you need new ECU software or a bunch of tricks.

Speedy G

Wouldn't the ECU just meter the fuel according to demand and the feedback from the O2 sensor? So you might get some benefit anyway - or am I talking b@ll@cks?

Speedy - so what you are saying is that 4FPR only makes sense with a purpose remap? Tell that to the legions of Seat boy racers who have done 4FPR combined with a straight chip job...

Thinking some more .... it's only a regulator - if the pump can't supply fuel at 4 bar you've gained nothing. Anyone know what the rating of the standard fuel pump is?

PS cheap mod though - they're on the IP site for around

Revo-tech have a 4bar software for the 4bar FPR. Talked to a Swedish tuner and he said he could adjust the software of his chip to the increased fuel preassure if I also wanted to change the FPR when chipping. This will help maintain higher boost at higher rpms = more power:D

Chrille, no it won't help maintain more boost at higher rpm. That's defined by the aerodynamic properties of the turbo, and that alone. It will help maintain air to fuel ratio at higher rpms if you're going lean without it. This only helps if you're going lean, which means you have a turbo that can supply more air than the injectors can supply fuel. Cars with the K03 sport can benefit a bit from this. If you do a K04 conversion, it's quite helpful.

Regarding the flow rate of the fuel pump, it's good enough for 250whp at 3 bar and like 16psi at redline when running at 4 bar. In other words, it's plenty for a K04 conversion, since in fact, it's the same pump as on the TT225. Unless you're running a much bigger turbo, you don't need to replace it.

Speedy G

Originally posted by Speedy G in this post

Chrille, no it won't help maintain more boost at higher rpm. That's defined by the aerodynamic properties of the turbo, and that alone. It will help maintain air to fuel ratio at higher rpms if you're going lean without it. This only helps if you're going lean, which means you have a turbo that can supply more air than the injectors can supply fuel. Cars with the K03 sport can benefit a bit from this. If you do a K04 conversion, it's quite helpful.

Regarding the flow rate of the fuel pump, it's good enough for 250whp at 3 bar and like 16psi at redline when running at 4 bar. In other words, it's plenty for a K04 conversion, since in fact, it's the same pump as on the TT225. Unless you're running a much bigger turbo, you don't need to replace it.

Speedy G

SpeedyG.

Thats's what I meant about higher rpms, it does alow higher boost without the engine running lean att high rpm's. Thanks for the more detailed info

/ Christian

A lot of tuners use the stock 3bar fpr when putting out 220-230 bhp. It's nothing wrong with that, it's just that the injectors probably will run close to dangerous dutycycle.

In other words, it would be interesting to see what the longterm reliability on the injectors will be with programs running them to the limit when on higher outputs.

With the 4bar fpr and the right ECU-software the injectors will work less then the 3bar fpr, due to more fuel per dutycycle.

That will result in a safer use of the injectors at higher outputs aswell as better atomisation.

/FD

Originally posted by KLB in this post

I've done a little Google searching, and found it's a reference to fuel injector pressure (4 bar = 4 atmospleres, or just a little below 60psi). Sounds like it's not far from diesel injector pressures.

PD diesels have enormouse injector pressures...... 100's of bar, 4 bar is nothing relative to them.

3 bar is typically the std FPR pressure, but some run 3.5bar FPR, and a squeeze applied to a 3bar FPR gets you 3.5bar (when tested)

>80% duty cycle on full chat throttle, high rpms is abaout as high as you would want to run fuel injectors, hence higher FPR's

Bill

Was that a turbo spooling up? Or was it a dump valve popping? Or was it just the sound of all this going over my head?

Damo

Damo - a regulator does what is says on the tin - regulates pressure. The fuel pump pumps fuel along the pipe at whatever rate it can manage. The regulator reduces that pressure to a known value and smooths it so it is at a nice constant pressure rather than pulsing with the cycles of the pump. The fuel is then fed to the injectors at that nice constant pressure so that as the injectors open and shut, the same amount of fuel is injected each time. The ECU varies the duration of the opening of the injectors to increase or decrease fuelling to the engine.

Does that help at all?

just to bump this topic. Has anyone fitted this to a standard vRS and notice the half a tank issues?????

i run a 4 bar fpr... the car runs fine with my apr s/w not sure why you would need a special map for 4bar.. sounds a little strange to me as the fueling delivered is requested by the ecu according to the readings it gets from various sensors.. if it gets more fuel it will run rich for a microsecond then adjust - hence reducing the injector duty cycle.... thus my injecotrs are working less to achieve the same power.. by the same token swapping the injecotrs for larger cc ones will also not require a special map to work - thats not to say a special map wont help get the absolute max but thats what v-tune is for

as for the half tank issue... i havent run enough tanks through to really tell...

but the stock fuel pump would seem a good place to upgrade next....

i run a 4 bar fpr... the car runs fine with my apr s/w not sure why you would need a special map for 4bar.. sounds a little strange to me as the fueling delivered is requested by the ecu according to the readings it gets from various sensors.. if it gets more fuel it will run rich for a microsecond then adjust - hence reducing the injector duty cycle.... thus my injecotrs are working less to achieve the same power.. by the same token swapping the injecotrs for larger cc ones will also not require a special map to work - thats not to say a special map wont help get the absolute max but thats what v-tune is for

as for the half tank issue... i havent run enough tanks through to really tell...

but the stock fuel pump would seem a good place to upgrade next....

All within fuel trim levels on the window tho... WOT does'nt run closed loop does it? Runs off tables under those conditions..

Wot?

wide open throttle!

Whats the part number for 4 Bar FPR for occy RS -03?

Gentlemen, what's this "Half Tank" issue I've seen?? I've had a 4bar FPR from the A4 1.8T on my A3 for.... over a year now, and haven't noticed any differences :confuse: Is there something that I'm missing??

Thx, :cheers:

half tank = perfmance drops off in second half of tank - like the pump pick up isnt good?

Is it THAT noticeable?? :confuse:

:cheers:

more a "butt dyno" thing really but a number of us have noticed it...

Ah, OK then, Thx. You had me worried for a second

:cheers: