running_cold924

two words. pulse width. a huge drop when injectors open and close. i think i remember seeing (when my pressure gauge worked) a 10-15 psi drop when the injectors open/close. went with the 83lbers cuz no more need to upgrade really (like you mentioned for your build). I know I'll never outflow them. I was up for the 72lb injectors but John at Vitesse talked me into the 83s.

you ought to see that needle bounce when at idle. all over the place! no more gauge for me. well, only for test purposes only.

the injectors are running in semi-batch with the engine pulling vacuum, then under some positive pressure, they switch to batch. it idles very well, doesn't load up, nothing. perfect power.

m73m95

Still doesn't make sense. (I'll say I do not have a gauge on mine...its in the mail though)

Like I said before, the fuel needs are the same. When the injectors fire at idle, they are open for a lot less time than the smaller injectors would be..... but the amount of fuel dispensed would be the same.

I'm not going to say you're wrong.... It just doesn't make sense to me why the pressure would vary to much... especially with the damper in place.

Also, my fuel pump doesn't make any different noise.... so I can't imagine why yours would. What pressure are you running? That is the only thing that would stress the pump.

choinga

I have 83#'rs because that's what John was selling with the MAF at the time and what the chip map was programmed for. They run great and the car idle's smooth. I didn't really notice that much difference in the sound of the injectors (they are noticeably a bit louder, of course) or my fuel pump.

I don't have any proof that the injectors are what blew my gauges up...just know that one worked fine for the year I had the car (and for probably 2 years prior when the PO installed it) and within a month of my MAF upgrade it was stuck at the maximum reading and tapping on it makes the needle flop around. So, I installed another one...the needle shakes a ton...I didn't see huge variations between pulses but the needle was getting a workout, that's for sure. The new gauge (different brand) lasted a few months. I'm done for now...I may buy another one for testing, but I'm not going to leave it installed.

running_cold924

exactly with mine...and not blaming Vitesse either, lol

i'm only running the non-adjustable 3-bar bosch regulator, nothin' fancy...

From Vitesse site: Normal batch injection with the stock DME software fires all injectors twice per cycle. Semi-batch fires the injectors once per cycle for twice as long allowing large injectors time to flow properly in low flow conditions such as idle and cruise.

Chris White

The reason the larger injectors make a difference is that you are opening a much larger ‘valve’ and letting a lot more fuel out of the pressurized system. The instantaneous pressure drop will be much greater (and that is what the damper is trying to ‘damp’).

This may give you fuel pressure gauge a little more of a work out – mounting the gauge to the fuel rail is ensuing a short life for the gauge as well.

#80 injectors are not overkill – especially in a batch fired system, I run 72lb injectors on most 2.5s and I they can run over 90% duty cycle at 18psi. If you are running E85 you will have problems getting enough fuel into a 2.8 a higher boost levels (and if you are not running higher boost levels why are you bothering with E85!!!)

running_cold924

I believe the first paragraph is another good point, thanks Chris. very true about the gauges, they hate life with the 83lbers...

Paulyy

Tree hugger

I've ruend around 4 gauges. Im not going to bother with another gauge untill i decide to install the turbosmart adjustible FPR with the gauge on the FPR itself

fast951

At Idle, to get a predetermined AFR the engine needs the "same" amount of fuel. It doesn't matter if you have stock or larger injectors. The larger injectors require less time (duty cycle) than the smaller injectors to supply the same amount of fuel. With the larger injectors, the duty cycle get to be very short when operating in batch; short enough that the larger injectors are no longer controllable in batch mode.
This is why we rewrote the code to provide semi-batch when needed. In semi-batch the injectors fire less times but for a longer period. So you get the injectors control back and we supply the correct amount of fuel.
At the end, the fuel exiting the fuel rail through the injectors remains the same between the large injectors and the smaller ones. Of course the time it takes the particular injectors to deliver the fuel will vary. I run 95# injectors on my car, my fuel gauge (liquid filled) is rock steady. A different brand fuel gauge bounced. From a safety point, I do not recommend keeping the fuel pressure gauge connected. I use the gauge to verify the pressure then it's out.
Measuring fuel pressure at idle is not a complete indication that your fuel pressure is fine. Fuel pressure must be also checked under load if there are reasons to suspect fuel starvation (lean condition). On the dyno, verifying the fuel pressure under load gives us good data.
Unless you are using a high quality gauge, preferably electrical sensor with remote gauge, I see no need to keep the fuel pressure in the engine bay. As is, there are many parts that could cause a fire, why add another item to the list.

Chris White

My old street car had a digital fuel pressure gauge that replaced the dead clock. The readout was about the same size and it was always fun to watch the passenger try and figure out what they were looking at.

John – do you know what the stock injector on time is at idle? I have never measured it but I imagine it’s a lot more than the 1.5ms (+/-) that I see with the large injectors! BTW – John’s system of rewriting the code to semi batch is really key to good idle with large injectors and a DME system. There are other ways but most are really just detuning the timing so that the idle is not overly rich.