oh c'mon.... all i did was do a little reading. I wish I were an engineer...i definitely missed my calling...

No i don't sorry, but it's the same as stock..so whatever it is, it's the correct one. If oyu have a spare/disassembled head, you can make a few measurements and calculate the angle (you will also need the lowest-most intake manifold..the runners wherethe injectors mount).

I see where you coming from now. THe boost will not be 'pushing back' so to speak into the rail/fuel plumbing, hence the fuel pressure is not affected by boost so far as this is concerned. Differential pressure is important becasue it equates your current fuel pressure and boost condition to what you would effectively have if you were under 0 boost (ambient 1 bar absolute). Hence, differential pressure is your fuel pressure minus boost ... period. In your case, that's 47psi - 8 psi=39psi=2.69 bar.

I think I see what's going on. I assume that you have a stock fuel pump...is this right? When you answer this, I will be able to answer your question. I think that what's happening is your large injectors supplied only by a stock fuel pump are draining down the fuel system to the point where the stock fuel pump can no longer maintain a high enough flow to keep things at 53 psi fuel pressure. Once you fall below the stock fuel pressure reg value of 53 (in your case), the fuel pressure reg is effectively shut off, and the entire pump output is directed toward the fuel rails. The fuel pressure will fall below 47 psi even more if yo uup the boost above 8 psi (you will see this is your injector duration stays constant of course).

The whole thiong with fuel pumps is that they have to be large enough to maintain a flow high enough under ALL conditions that the car will see while keeping the same fuel pressure. So, at idle, your fuel pressure is 53 psi, but your flow is...say...61cc/min (total). At full boost at redline, if you had a correct fuel system (assuming just big enough pump and not manifold-referenced FPR), your pressure would be 53 psi, to stay consistent, while your flow would be 2452cc/min (510cc x 6 x 71% duty cycle, going off my car's example). In your case, the fuel pressure falls below your set 53 psi at full WOT/boost because of very high flow..it just can't flow high enough and maintain the set fuel pressure.

Anyway..HTH

 

440cc injectors are perfect up to about 450whp, so nothing changes in that respect. The RC injectors are accurately rated, and the PE injectors are a little bit underated. The 510's are going to be sufficient for about 570whp at 100% duty cycle. Gurgen, the 622whp I got on the 550's was getting very creative with fuel pressure..and I would recommend 650cc injectors for anything about 570whp.

 

No I have a Walbro 255 lph pump...the fuel pressure at ambient atmospheric (~14.7:1) is 53 PSI. The fuel pressure in my car does not drop until boost is applied. In other words driving around in vacuum or at 0 PSI manfiold pressure my fuel pressure shows at 53 PSI. When I apply boost my fuel pressure drops a bit with the final amount being 47 PSI of fuel pressure at 8 PSI of manifold pressure. I think this is exactly what you are describing. For our sake I guess the accurate number to start with is 53 PSI as that is fuel pressure at atmospheric.

 

Sharif,

The 440s from the Greddy TT kit are RCs right?

 

Yes they are....

 

Sharif,

what was the fuel pressure with your 550's at 622whp? I am going from my own account that 490 hp was achieved on PE 510cc's with 70% duty cycle and only 47psi of fuel pressure. This was before I applied CJ's correction kit. What I am saying is that you can run at a very safe 4bar (58psi) baseline/differential pressure and achieve 634cc/min flow rate, which makessense. So if you achieved your numbers at around 58-60 psi differential fp, then that's exactly it. I am not saying that you can do much more than that with ultra-safe reliability. However, there are many that believe that these injectors can VERY SAFELY do 5 bar differential for long periods at a time. You can certainly do this safely in short burst, like in a street-driven car. I do not intend to go over 80% duty cycle on my setup, realizing that these are not peak-and-hold injectors. I'd rather go with high fuel pressure first, it only helps atomization, not that many multi-nozzled injectors need them that much.