[urq] EFI + MAC-14 maxing ataround 5k RPM

Ben Swann benswann at verizon.net
Tue Oct 23 19:17:45 PDT 2007



I’m not totally up on the injector ratings, but understand in my reading MS works fine with the type of regulator I’m using – it has a manifold pressure reference port.  So under vacuum, the pressure is somewhat lower than pressure set at atmospheric (45 PSI).  Under boost, the fuel pressure goes higher.  I may have the pressure set on the high side, but that was how the car started best and jibes with megasquirt recommendations  The VE (volumetric Efficiency) and other tables that are used to tune are not linear and can be set to compensate for the effect you describe.  


I am finding despite all the theoretical and applicable books I’ve read  - max Boost, EFI perf tuning, etc. all seem to be muddy details that need to be sorted out.  I suspect there is some base setting for pulsewidth that needs to be tweaked.  





From: QSHIPQ at aol.com [mailto:QSHIPQ at aol.com] 
Sent: Tuesday, October 23, 2007 8:21 PM
To: benswann at verizon.net; speedracer.mark at gmail.com; antar at comcast.net
Cc: urq at audifans.com; quattro at audifans.com
Subject: Re: [urq] EFI + MAC-14 maxing ataround 5k RPM



Maybe you know this already...  

These are normally rated injectors at 3bar fuel pressure *DIFFERENTIAL* (= vs manifold pressure).  Which means exactly that the fuel output goes down as the fuel pressure differential goes down.  Even no load, you need to have 3 bar pressure differential, or the software isn't going to work right.  IIRC, MS assumes Fuel Pressure Differential as a constant x.x bar for software table purposes.  Remember, the lower the vacuum, the higher the fuel pressure required, a 5k no load rev could be enough.  Do you have manifold reference to the Fuel Pressure Regulator?


The other thing I would look at is disconnecting the fuel pressure regulator return line insert into a gas can, and try the rev test again.  If you have no fuel coming back to the tank at high rev, you have a fuel starvation problem, pressure or flow.




Scott J



In a message dated 10/23/2007 7:13:04 P.M. Central Daylight Time, benswann at verizon.net writes:

I have had some conflicting information on them – I originally had information they were
42 lb/hr and purchased as:

Injectors are Blue Top 42 lb/hr or stock AAN blue                    2.4       210
2.55     pintle (1)

I found other info. on them  -

D3165BA are 37 lb/hr Delphi-Lucas RS-2 equivalent.  These are supposed to be good for
use in an RS2 upgrade to an AAN/3B engine, so should handle my fueling requirements



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