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Re: How safe is above normal boost?
re: Ur-Q MAC CPUs
What happens when you go over 16 PSI and the sensor goes non-linear?
It doesn't go non-linear, it just pegs. (Well, I guess you could consider
that as "non-linear"). 16PSI aka 30PSI absolute is about 5 volts out of
the transducer, which is 0xFF byte value (aka "positive infinity"), and
that's as high as the ECU can measure, and that's when it shuts off.
THose who have measured the transducer itself tell me it is linear until
more like 40PSI or so (36? 48? well over 30, in any event), but the ECU
can't read it cuz its A/D converter is maxed out. YOu need to scale the
transducer output (e.g., via a voltage divider) in order to allow the
ECU to read higher levels, and you have to "scale" all the ECU's maps
by whatever you've done to the transducer signal feeding the A/C conver-
ter input. Simple enough, mostly tedious (and the risk of missing an im-
portant map entry somewheres, etc.)
Do you just get nice, steady max ignition timing retard at boost pressures
above 16 PSI?
If you don't alter the maps, you get whatever it normally provides at the
stock max of 11PSI or so. But I doubt it makes too much difference, theres
not a lot of delta at the upper end anyways. From what I gather, the stock
MAC-02 timing map is very conservative timing, so a few extra PSIes are
not a problem (run 93+ octane, etc., and so forth). I haven't the foggiest
idea what the limits and margins are. The engine itself seems to readily
handle 16PSI boost levels (lots of people out there running 18PSI springs).
Do things remain "stable"?
Right up until it turns into shrapnel . . .