As a few of you know, I have just converted my tbi (xfire) 383 from a 7747 ecm to a '8625 pcm. This has given me the ability to datalog MUCH more info.
Previously I didn't know how hard my injectors were working, but now I can read both the BPW and Duty Cycle from datamaster.
Tonight I raced at the track. Peeled off a few 12.8's (~390 chp), same as before. The interesting thing is that datamaster reports that my 90lb injectors at 15psi are reaching a peak of only 46%DC!! The idle is really good also, it is just on the threshold of dropping back to async mode, but i could easily create a safety margin by lowering the pressure and still have enough for the top end.
I have a few more plans for this thing, including bigger TB's and a bigger cam. I now know that fueling is not going to be a limit for a while yet.

 

I find that rather hard to believe. I'm runing up in the 70% now with 70lb/hr at 22psi. Those numbers seem awfully low for some of the biggest HP numbers that I have ever seen from TBI. I'm not calling BS I'm just woundering why your combo takes so much less fuel than most of the others I have seen. There might be something to the way that ecm fires the injectors.

Are you shifting at 3000 rpm lol

 

I would be concerned that DataMaster isn't calculating the DC% correctly. I'd bet that the reported DC% needs to be doubled. . .

RBob.

{edit: BMmonteSS beat me to it, what he said. . .}

 

Ain't gonna happen.

Like RBob said, somethings being calculated wrong.

Need one of em DC Meters

 

You can verify the incorrectness of the calculation by dividing the "On time" of the injector by the "available time," which is found by the RPM and the number of injections in 1 revolution. If your math is a little rusty, on a 2 injector setup, which should fire each injector alternately, i.e. 1 injection per intake stroke per cylinder, it comes out as Duty Cycle = RPM*(2/60000)*(Injector milliseconds)*100% for your 2 injector, V8, alternate injection application. The 2 is for number of injections each injector makes per revolution, the 60000 is for the number of milliseconds in a minute. So, at 6000 RPM, a PW of 5 milliseconds for each injector should max it out.

 

It is a bit hard to believe isn't it..
I'll calc it manually from the PW and RPM and report back.

 

Once again, you guys are right and Datamster is wrong. It IS reporting only 1/2 the actual DC!! Its not the only bug I have found, so I'll double check every unbelieveable thing it tells me from now on. ;-)

 

Eww 92% duty cycle......but then again your feeding almost 400 hp with only 15 psi!!!!!!!!!!!

 

Is this with a 2 injector or 4 injector (i.e. Holley) TBI setup? And, static or vacuum referenced FPR?

 

2 injector crossfire (x-ram) setup ( i removed the 4bbl about 2 weeks ago)
Static fp at 15psi.

 

Another item is that the ALDL reported PW is not always the final as injected PW. With the TBI ECMs it is common to add the Injector Bias after the PW has been reported via the ALDL stream. A quick look reveals that the $E6 mask does the same.

This makes the real PW at the injector greater then the reported PW. And recall that the async AE fuel needs some time too. If the sync DC% is 50% then the async AE has a 50-50 shot of actually being included.

BobR.

 

You never cease to amaze me with your knowledge! I am planning a cam swap later this year, so i'll have to increase the pressure when that happens..