[Shadowraven]

So I need to consult the hive mind regarding fueling on a VVT turbo (2860RS, stock block) and what the limit of the stock system is.

As I understand it the VVT car has a returnless fuel system, which is referenced to atmospheric pressure. Unlike the NA NB cars it therefore cannot increase fuel pressure in line with manifold pressure changes and so adding boost causes a proportional drop in fuel pressure. Some people suggest that the fuel pressure drops towards redline even on a stock car, and therefore an uprated pump is required for the VVT cars. However the VVT cars also run a higher fuel pressure, 60psi rather than the 43psi in the NA and NB.

As I understand the NA and NB fuel pump is good for about 300hp, but what about the VVT?

If fuel pressure in the VVT drops towards redline, provided the injectors still have the capacity can I not just add VE and would only need a pump should I run out of injector duty? The VVT system is 60psi, even falling to 40psi at redline 640cc injectors are still enough for 300whp, so if I still have over 100hp of headroom on the injectors, surely I could just not upgrade the pump and run the injectors at a higher duty?

Would upgrading the pump even really be of much use as it doesnt really address the cause of the issue - the fall in fuel pressure. If the regulator is atmosphere referenced, surely it is going to see pressure drop with boost regardless of the pump in it?

I was under the impression that generally you only really need a pump if you're running small injectors and want to artificially increase them, or you are using so much fuel that the pump can longer maintain the required flow. If the pump is the same as in the NA NB cars then can it flow enough for 300whp? The VVT pressure drop makes things complicated, but at the same time the pressure is higher (60 not 43), so I duno if the moaning about pressure drop is even relevant if it's dropping from a higher base line down to what the NB is as standard anyway provided you don't run more than 17psi boost.

 

[atlex]

there's a factor of x flow at x pressure you should think about and a decent pump should have specs for that. as the pressure goes up the flow goes down....

Walbro Fuel Pump Performance and Pressure Charts for example

you should look for a pump that will flow enough at the o.e. NB rail pressure i.e. 60-63 psi

if you retain the stock NB FPR it will be 60-63 psi

in your ecu you should spec the flow rate at the rated flow for the injectors. i.e. 640cc @ 43 psi (or kpa equivalent)

and then specify the regulated fuel pressure as per your fpr

 

[atlex]

also for boost reference you should add the psi to the fuel pressure, this is technically the job of the FPR

20 psi boost would mean 80 psi fuel pressure if you've got a 60 psi fpr

 

[Shadowraven]

Thanks but not sure how relevant any of that is. The flow Vs pressure argument is exactly why I'm asking, and the main question is whether the flow will still be sufficient even if the pressure dropped, as detailed in my question. As I said only the 255lph pump can flow enough at the rated pressure, but it's too much for the regulator and causes idle issues so isn't a great solution.

It also doesn't resolve the pressure drop issues as those are due to the regulator being atmosphere referenced.

Bit stuck for ideas unless I convert to a NB style system. But the point of this thread was to ask if that'd actually be required as I'd really rather not do it. If it was a requirement I'm pretty sure it'd be widely known.

 

[Reverant]

I'm running a 255lph Walbro on my Mk2.5 VVT with ID1000 injectors. No idle issues and the fueling is enough for 29psi on my GTX3076 (something like 88% max duty). Adding a regulator and return like would add about 10-15% more headroom.

 

[Shadowraven]

I'm running a 255lph Walbro on my Mk2.5 VVT with ID1000 injectors. No idle issues and the fueling is enough for 29psi on my GTX3076 (something like 88% max duty). Adding a regulator and return like would add about 10-15% more headroom.

Cheers. Is the OE pump good for 240bhp on 640cc injectors (gt2860rs, likely 10psi)

 

[Reverant]

I've never done a turbo car without a fuel pump replacement. If you are on the original Mazda pump, it's due for replacement anyway and a genuine Walbro is cheap.