<div class='quotetop'>QUOTE (Anh Bi @ Oct 25 2007, 06:25 PM) [url=index.php?act=findpost&pid=8078]<{POST_SNAPBACK}>[/url]</div>
The Walbro can produce enough pressure to push the flow of your stock injectors, but the safer choice is to upgrade your injectors as well and have them controlled with a full stand alone ECU.[/b]
Your average Port Injection (PI) motor pushes around 43psi worth of fuel pressure, whereas Mazda's DI motors push around 1600psi worth of fuel pressure. The extreme pressure is needed for a couple of reasons, the first being Mazda's DI motors only inject during the Compression stroke, so the pulse width is incredibly narrow, they must inject a very large amount of fuel in a short amount of time. They also fun a very fine spray pattern, which is another reason the high pressure pump is needed.
The high pressure pump itself is cam-driven, meaning the amount of fuel pressure the motor receives is directly related to RPM. It's a known fact that when tuning the DISI motors on the stock turbo they begin to run out of fuel in the lower RPMs (around 3500rpm), and if you swap to a larger turbo, the pump runs out of pressure in the higher RPMs (above 6000rpm). Replacing the in-tank pump will do little good, as it's the high pressure pump that's running out of pressure. This has been proven many times. If you were familiar with VW's 2.0T FSI motors or DI Diesel motors, you would realize, in DI applications boring/upgrading the HP-FP is fairly common when pushing more power, and that replacing the low-pressure in-tank pump typically isn't a consideration.
Although even if the HP pump wasn't the weak link in the fuel system (even though it's been proven that it is), your ideas are not options for the Mazdaspeed 3/6 community. For a variety of reasons:
1. There are no injector upgrades currently available for the DISI's direct injection motor. Due to the precise spray patterns, and tolerances you cannot simply use standard RC style PI injectors. So scratch that.
2. Even if there were larger injectors available, there are no standalone EM devices available for the MS3/MS6. Although your logic is flawed, there is no need for a full standalone even on PI motors when just swapping to slightly larger injectors. In the Subaru/Honda/Mitsu/ect community, it's been proven time and time again, that typically an ample piggyback (like a UTEC, Delta, XEDE, ProCEDE ect) or flash based tuning device (like an AP or tuning software) can allow you to control and tune larger injectors.
3. I'm very familiar with the Walbro 255lph... apparently you're not familiar with the DISI's fuel system as it's
return-less. Meaning no return line the the in-tank fuel pump... unlike a Walbro, which does in fact have a return line. If you try to run a return-style FP in a return-less fuel system you WILL, I repeat WILL burn out the pump itself. SRT-4 guys run a return-less system just like the DISI guys, and when they get to that point, what do you think they do? They swap over to a Walbro, however it requires tapping the fuel rail to run a return line back to the Walbro.... now I would certainly hope someone wouldn't be so careless as to run a simple tap-line on a DI motor's fuel rail, as they hold about 1600psi worth of fuel pressure.... as opposed to 43psi.... not to mention you would be circumventing the HP pumps spill valve.... it's all around a bad idea.