Speed Density Tuning - FAQ
#21
#22
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What I suggested above was an appropriate method that can be applied to ANY Stand alone ECU. it was not and was never EVER suggested that it was specifically with respect to a stock pcm. This thread is including ALL Speed Density ecu. Therefore my applied principle is good for any people reading this who do not have an OEM ecu, of which there are plenty!
2. It will work just fine with a stock PCM. Last time I checked, if something works correctly, that is the same as being correct. If you are using EFI and I am using a carburetor, I am wrong because the method I chose is slightly less fuel efficient?
3. the post was more about WHY and WHAT not necessarily meant to be a how-to. The end user establishes their own method for implementing the fuel in the manner I discussed after reviewing the capability of their own computer/ECU. What I provide was an example of how to with any ecu, as some are quite the bare-bones essentials (mega squirt sometimes, and power FC for example)
Last edited by kingtal0n; 08-12-2016 at 06:39 PM.
#24
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FWIW i found a better way than a gallon of text to show for this FAQ what I mean, and I will provide a picture (1000 words in a picture) soon and they can delete all the garbage and leave the picture which will perfectly explain the procedure I am trying to describe here.
Last edited by kingtal0n; 08-15-2016 at 11:51 AM.
#25
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Bottom line, all this theory, fact or proof if any leads to what? Engine longevity, cleaner emissions, more power? I think none of the above..Who cares when you lift the A/F dips into a slightly lean condition, again for how long, a millisecond? what does this all prove, ok now your lean dip is instead of 15.1 its now 13.8, your cylinder wall wetting is now this and now that. If all this gives you the satisfaction of attaining a certain goal for yourself, then thats fine, but to this forum, I dont think it helps many if any one trying to tune their own vehicles..
#26
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Bottom line, all this theory, fact or proof if any leads to what? Engine longevity, cleaner emissions, more power? I think none of the above..Who cares when you lift the A/F dips into a slightly lean condition, again for how long, a millisecond? what does this all prove, ok now your lean dip is instead of 15.1 its now 13.8, your cylinder wall wetting is now this and now that. If all this gives you the satisfaction of attaining a certain goal for yourself, then thats fine, but to this forum, I dont think it helps many if any one trying to tune their own vehicles..
Plus it gives us a healthy margin for error in speed density tuning where a tiny, negligible amount of fuel (less than 1ms for sure) in high vacuum regions will help compensate for fluctuating temperatures elsewhere. In Florida I tend to avoid pulling fuel for higher IAT in turbo cars; the factory is trying to save fuel, while we are trying to save the engine.
Here is a random fuel map from search internet images. Notice how generally you see this red, super lean portion in the high vacuum region. It typically saves fuel, causes harmless misfires, and precedes the fuel cut. However in engines with modifications, it can become a detrimental setting, if the user is slightly on the pedal (remember some engines have larger throttle bodies which move a large portion of air per a very small movement of the blade) the A/F will be lean, and as the user tips into the throttle the A/F becomes even leaner despite the accel enrichment, Which is often too little or non-existant when the throttle is moving very slowly (the sensitivity and age/year/mileage of the TPS sensor and it's computer/wiring are factors which determine sensitivity as well as electrical noise) in other words, sometimes the TPS or should i say dTPS (rate of change of TPS) does nothing when the user is tipping into the throttle on some engines (especially 1990's and early 2000's) and as the user steps down slightly the pressure drop can be significant, the A/F starting off lean, becomes leaner as the compression increases (VE goes up when you step down more on the throttle) and this can generate a series of engine knock before compensation from new fuel values, and steady state conditions are allowed to come back.
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Now with the new setting, you tip into the throttle at 5000 or 6000rpm and instead of being met with a 16:1 or worse, you get a nice 13.something. Remember this 5k rpm, the last place you want a 16:1 I dont care what the vacuum of the engine is, you better keep that cylinder wet if this is a high performance turbo engine making 180hp/liter or so because conditions can change rapidly with very little throttle movement at those engine speeds.
Last edited by kingtal0n; 08-16-2016 at 07:22 PM.
#27
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,
Using your numbers ( rounded )
for MAP sensor 1261-5136
Linear 200
offset 8.
Is there benefit to shifting, or adjusting the OFFSET term so as to make local atmospheric pressure exactly match KeyOn MAP sensor reading ?
.
Done once, this should allow accurate MAP readings, and indivually calibrate for the installed MAP sensor... Am I thinking correctly ?
Using your numbers ( rounded )
for MAP sensor 1261-5136
Linear 200
offset 8.
Is there benefit to shifting, or adjusting the OFFSET term so as to make local atmospheric pressure exactly match KeyOn MAP sensor reading ?
.
Done once, this should allow accurate MAP readings, and indivually calibrate for the installed MAP sensor... Am I thinking correctly ?