The commanded PW will vary with MAP, load, RPM, temperature etc. For all the compensations to work correctly the fuel volume must be directly proportional to PW. So for example if the PW is increased by 10% then you want to get 10% extra fuel.
Below is a picture of an injector test for determining SPWA. The straight dotted line is what the injector should flow if it was perfectly linear. The other 4 coloured lines are what the injector actually flows (f different injectors)
You can see if I was operating at around 0.4ms PW my injector flow would be about 42cc/min average. Now say the AC just turned off and the ecu calculates I need 20% less fuel, so it reduces the PW by 20% so Im now operating at 0.32ms, you will notice my average flow is still about 44cc/min. So the ecu has just commanded a 20% reduction in fuel but it has actually got 5% more. This means you are now about 25% too rich. Now lets say you change down a gear and the ecu calculates the engine needs another 20% less fuel, so our PW is now 0.25ms, at this PW our average flow has dropped to about 17cc/min. So this time the ECU has commanded 20% less fuel but actually got 60% less.
The idea of SPWA is to straighten out this erratic PW to flow relationship. So at 0.4ms commanded PW a SWPA of 0.05ms would bring the flow up to the desired 50cc/min. At 0.3ms the SPWA would be about zero as the average injector flow is close to the desired already. At 0.25ms PW a SPWA of about 0.035 would bring the flow up to somewhere around the desired.
Our GTR base map came from a near stock car one of our tech support guys tuned on pump gas. I pulled a few degrees out of it already before making it a "base map". I cant remember how much exactly but from memory something like 3-5deg in the boost areas.
Yes, that would likely be knock free on stock compression ratio and common "western" fuel. Note however, when you increase advance the engine noise will increase, so this strategy of building a threshold based off a retarded run is not always very useful.
LeeE got a reaction from Vaughan in Map Limit 3D Table
