On my '99 M3, with a 3.2l 10.5 static CR engine, IM running a Vortech supercharger (centrifugal) making 11 psi boost at redline.. And, Im running no intercooler, at the moment. That will soon be rectified, but for the purposes of this discussion, assume no intercooler.
AFRs are in the 11-13:1 range. No knock has been evident.. Intake Air Temperatures while cruising, since there is no intercooler, and since its before the water injection triggers, are high... Generally about ambient plus 70-80 degrees. If Im doing a WOT run, I will typicvally see my IAT values near 175 degrees at the beginning of the run, which will drop to near 115 degrees at redline, which is 7000 rpms!
Im using a .8mm jet. Now.... I used to trigger at 4 psi, which its around 4000 rpms. Recently, Ive found that I can trigger this nozzle at about 2.75 - 3 psi, which hits around 3000-3300 rpms, and NOT experience any stumble or stutter, at least, that I can feel.
So, Im wondering, is there any reason I shouldnt be triggering so early? Since I perceive no fall off in performance when it triggers, I ve thought that the best place for me to trigger, since I have no intercooler would be as early as possible. On my car, Timing is strongly effected by the IAT sensor. So I feel its to my advantage to trigger early.
There is a good water to air aftercooler unit which should add about 20-25 whp to my current setup... The aftercooler has been instrumented to show that where my IAT value are in the 170s during cruising, they will be near 110, and with the combo of the aftercooler Plus my water injection, they will be in the mid 90s in summer weather. When I install the aftercooler, I will raise the trigger point to around 6 psi, as I dont believe I will continue to need it to lower my IATs at lower rpm levels, and will instead use it to suppress knock, which, because my injectors are near max above 6500 rpms. Still, they currently are able to sustain a 13:1 ratio at redline. Everywhere below redline, its in the 11s and 12s.
Does this sound reasonable?
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Paul E -
'99 White M3; < 69K miles; Dinan SC kit with 6" RMS crank pulley and water/air Aftercooler: 11 psi-367 SAE rwhp/304 ftlbs; Custom Tuning by Nick G; AA Aquamist Water/Methanol Injection and AA exhaust; Fikse FM-10s;
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