Beakmoney

so i've been dreaming up ways to integrate a map sensor into the stock harness, it dawned on me last night.

the only reason i want to use a map sensor at all is to retard ignition timing under boost. it would work in the same way an MSD BTM would, except controlled by the ECU.
most of us who are boosted (and alot who are not) no longer run our EGR valves. how feasable would it be to use the EGR harness/ECU output in order to referance a map sensor? all you'd really need is a voltage output map for whichever sensor is used, but i am completely in the dark about the software being able to do what i want it to do. the function would not need to be complicated either. at x voltage pull x amount of timing or at x voltage, the timing value is x.
what is the possibility if this working given the software thats availible to us?

Calum

....but you can program the ecu to be even beter than that without having to change anything. At least with a B13 this is now pretty straightforward (B14, needs some leg work, big surprise). Generally, most Nissan ecus run on the last column in the big maps (timing and fuel) under boost. Thats actually really handy if you don't know the max boost a user is going to run the car at; you just tune the car for extreme conditions (high boost) and leave that in the last column. Then the ecu uses the same timing and fuel curve for 7psi as it would at 14psi. Inefficient, but it works great.

To do what you want all you have to do is rescale the TP axis so the upper limits correspond to the boost settings you want (in other words, make use of more than just the edge of the map). The trick is having to know what TP corresponds to what psi, but with map tracing now available thats just a matter of experimenting and mapping it out (this will be car, or at least setup, specific). Now your better than just X retard at X psi, you can chart an entire timing curve vs rpm.

Beakmoney

forgive my ignorance, but running the same timing at 14psi as 7psi (given its tuned for 14) would not be optimal. the problem i see with rescaling the TP axis (i assume you mean throttle position) is that boost is not always the same in each gear at a given throttle position, for instance i start to make boost at about 24% throttle in 4th and 5th gear, whereas 24% throttle in first and second make alot less boost, if any.
now i know its a different breed of tuning but i think the same lessons apply. a friend of mine tunes alot of the local hondas, what he does when a wideband is availible, he map traces to find out what voltage the map sensor sees boost, and essentially builds a nice N/A tune on all map sensor voltages below that (fine tuned based on other people's maps, typically), as soon as boost comes on, he naturally changes the tune drastically to accomidate.
maybe its my wacky understanding of how the ECU works but its my opinion that a map sensor is less accurate than a maf except in controlling timing under boost. thus my reasoning to wanting a map to control only timing under boost as airflow could be 49% at 7psi low revs, or 49% at 0psi high revs, and the same amount of timing for both, or even a happy medium i think would be severly detrimental for the health of the motor (erring on the side of more timing, naturally).

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02 WRX wagon 5spd. reflash and other stuff..its still slow.

Calum

No, TP is 'theoretical pulsewidth'. Not related to throttle position, sorry for not specifiying. Its what the x-axis is on the main timing and fuel maps, and is directly related to measured mass air flow.

Running the same timing at 7psi as at 14 isn't optimum, but it does make tuning the ecu dead easy. And it isn't as big of a difference as you might think. I'm not advocating this as the optimum way to tune the ecu, its just one way to setup the ecu for making very 'generic' tunes.

A maf sensor is a very effective way of determining airflow, regardless of the pressure. Its got its ups and downs, but you can use it to your advantage. Check this out, if you tune with a map sensor for a setup on a T25, then change to a big honker T3/T4, your 'tune' will change, simply because the mass flow of the turbos is different for different boost levels. With a maf its all good, no changes needed.

Beakmoney

so theoretically if i set a timing retard based on airflow, increase boost above initial 'tune' everything should be fine?

Calum

Only if your initial tune is really for the higher boost level. You have to tune for the max boost your planning on running.

Beakmoney

again, please forgive me ignorance, i tune for the max boost, that means say i'm running 14psi, i will be running the same timing at 9psi as i would at 14? this is where i'm getting confused.