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Oh dear, some food for thought:
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Posted by Adrian W [Email] (more from Adrian W) on Tue, 14 Dec 2004 01:59:17 Share Post by Email
In Reply to: Correction....T7 does use both air mass AND pressure, perkj, Sun, 12 Dec 2004 16:03:27
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1. Did you know that the airflow through T7 varies more than 11% at peak power completely stock without any knock even on 100 octane fuel? (I've seen from 22-24.45 lbs/min - 5,500 RPM) You'll have a hard time convincing anyone of "more power" if the first or second standard deviation for stock values is greater than your claimed increases.

2. Hardware mods might force Trionic to boost a bit higher than it ordinarily would. But if the Air-Mass/Combustion values go beyond what Trionic "wants" the timing is pulled WAY back *without* any knock what-so-ever. Any decrease in pumping losses would be offset by a comparable decrease in thermal efficiency caused by the late timing. Example: Boost goes up 10% from "normal" values, timing drops 6 degrees, EGT goes way up, power stays about the same. Now your 3" exhaust might lower the EGT a bit, but it only cures the symptoms, not the disease; the real problem is late ignition timing which you cannot fix because Trionic is trying to "save itself" from the over-boost you created. That is a problem the better exhaust doesn't solve.

3. My MAP sensor says I'm getting around 11 psi of boost at this ambient pressure, my Autometer boost gauge says around 14-15 psi. You can argue which is wrong all you like, but if someone told me that the MAP sensor is frequently inaccurate in a putative sense I would not argue. The MAP sensor only needs to "correct" the MAF value with a *relative* change in perssure, not absolute. A slight change in VE would not alter the relative change between on-off throttle load changes, just the absolute value at each point. It would not alter the functionality of the MAP sensor. Even if this occurred in Trionic 5 the Multiplicative Adaption function would allow the MAP sensor to still work properly as long as you don't reset the ECU every time you drive the car. ;)

4. The modifications themselves should not alter the air/fuel ratio as both air and fuel are measured by either the MAF sensor or the RPM sensor and do not require any additional input. However, if the modifications force more air into the engine than is desired, the engine may end up at a different part of the fuel-map where there is a different programmed air/fuel ratio.

5. You guys *really* need to put some dataloggers on your car before you make mechanical modifications. If the air-mass/combustion (read: boost) goes up for any reason the timing will be reduced. There is no room for error as this is typical timing for a B235R at around peak-torque: http://img.photobucket.com/albums/v14/SaabTuner/100Octane_BoostVsTiming.jpg <--- if that doesn't scare you enough, think about the fact that it was done with 100 octane *race fuel* ... there was NO KNOCK. This is not an ECU I'd want to tinker with without being able to see all of the base-maps first. How do you know your EGT and timing aren't waaaay off-base? Remember, as I said before, T7 changes airflow 11% or more on a regular basis; a difference on a dyno-run does not mean an increase in power over stock.

Hope that gave you something to think about, whether you agree or not.

Adrian~

posted by 4.60.65...

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