Hey everyone is entitled to thier opinions and guess what... you are very correct. And p[lease correct me with anything I say cause thats the only way I'm going to learn. I couldn't agree more. My point was I seriously couldn't believe that the pump flowed as well as it did and the Walboro flows even more (wish my stealth would have had this problem). What I was wlooking for though was everyone saying that on the stock fuel you can only run safely about 21psi and from the A/F ratio's I think it could be done higher on the stock fuel system safely. Hell you should be able to run roughly 23 to 25 lbs with no problem with how these motors are set up on pump gas with the strock turbo. Or am I wrong on this? I'm basing my experience off of stealths/3000gt's since thats what I have worked on for the last 6 years. I'm still trying to learn on the 4g motors.

 

I wouldn't run over 23lbs unles syou plan on replacing head studs.

So is the consenus here that a welbro is not needed with basic modifications? That I could actually be losing power with the Walbro?

 

Side note .. 1.5 bar is 23psi .. which is what I used to run

Personal experience .. I ran a fuel pressure gauge using stock fuel pump ..
My datalog logs showed me injector duty cycles approaching 100% AFR around 12.0 (after fuel trimming down as I ran 10.x without adjustments)
Past 5000rpms .. the fuel pressure drops to below the 3.0bar differential (from 4.5bar to 3.6bar) all the way to redline

On the shop's advice I swapped out the fuel pump to walbro 255 .. viola .. back to 3.0 bar differential (43psi ) all the way to redline
Also injector duty cycles dropped to 90% or so .. (shows 10.x AFR too like what was mentioned)

after trimming back to 12.0AFR .. I get duty cycles around 80% and steady fuel pressure throughout

Point here is, you have to see the full picture before deriving a conclusion .. everything looked okay to me except for the weird drop in the fuel pressure.. and the exceptionally high duty cycles..

David made a good point regarding the boost levels as the fuel pump seems to drop in flow exponentially when the pressure is cranked up.. no solid numbers to prove this .. but it was derived from the pressure drop I observed ..

just my 10 cents worth (equivalent US5 cents )

 

gunzo,

This is what I've been preaching in not so many words since 2003... etc, etc.

 

Well just got back from dyno day and I must say I love the AFC. With the walboro fuel pump in and only about 20 psi I managed to pull 289 hp to the wheels. Almost a 70 hp difference between when I trierd to run the walboro with no tuning and about 40 hp more with the stock fuel pump. So I am happy. I will put up the dyno sheet tomorrow if anyone is interested.

 

Agreed, and if the computer works like the systems I've tuned...

At WOT (wide open throttle), the computer looks at only the MAF for data used (open loop) to make the fuel computation. Likewise, the computer cannot not detect changes fuel pressure (mechanically controlled). With the factory pump, there is a drop in rail pressure at WOT due to the volumetric limitations of the pump. The factory WOT programming takes this into account, and the WOT mixture is already too rich for optimum power.

With the higher volume pump, the rail pressure remains constant at higher power levels. This causes the WOT mixture to become even richer. The computer is 'unaware' of this, and has no means of checks/correction because the difference between the new and old pump is probably nil at part throttle (closed loop), so the computer cannot really 'learn' the new pump. The result is an even richer WOT mixture, which only reduces WOT power.

If this is the case, it would indicate that the fuel pump upgrade should be left only to those who possess a means of adjusting the WOT fuel mixture, and dyno tuning is almost certainly a must for those who upgrade the pump.