RomRaider

Sounds like the Tau / Wall wetting / Delta-Load enrichment tables.

See here: viewtopic.php?f=25&t=7442&start=150

and this viewtopic.php?f=15&t=1735&start=48

I have another theory about the tip-in compensation for boost error (TICBE? FIBET?) that I've been meaning to post up for a while now...

From first principles:

Tip-in is intended to compensate for increased airflow past the throttle plate after a rapid increase in throttle opening. It takes time for the increase in airflow to be evident at the MAF sensor, which is much further upstream, so tip-in compensates during the period of time between the throttle opening and the MAF sensor 'seeing' the increased airflow.

The increase in airflow happens because of the pressure differential between the region upstream of the throttle plate and the region downstream of the throttle plate.

So, tip-in should be larger during high vacuum than during low vacuum. In fact, I don't see a reason for any tip-in at zero MRP - if there's no difference in pressure between the IC-to-throttle-body pipe (upstream of the throttle plate) and the manifold (downstream of the throttle plate) then there won't be an immediate spike in airflow. But there's nothing in the ROM that acts as a tip-in compensation for that pressure differential. At least, not explicitly.

I sometimes wondered why the target boost table in my stock ROM had unrealistic values at low throttle openings - where the manifold is in vacuum (even deep vacuum), the table is just full of values of 0.77. I think TICBE / FIBET provides an explanation for that.

One side-effect of those unrealistic values is that boost error will be high when the manifold vacuum is high, and boost error will be low when manifold vacuum is low. The TICBE / FIBET compensation results in an increase in tip-in at high boost error (deep vacuum) and a decrease in tip-in at low boost error (low vacuum), which aligns nicely with my theory that tip-in should be somewhat proportional to vacuum.

I wonder if the OEM tuners thought this all the way through, or if they just noticed that tip-in was better with a tune where the target-boost table hadn't been filled in on the left side. Or maybe they did notice it, and they figured that a TICBE / FIBET table was a simpler code change than a "Tip-In Enrichment Compensation (Ratio of Atmospheric Pressure to Manifold Pressure)" table. Or maybe there's some reason they didn't want the atmospheric pressure sensor involved in these calculations. Or something else entirely.

Very interesting, great analysis and it makes a lot of sense!

i agree.

basically the "rush" of air mass isn't going to happen once MRP passes through 0psig.

it is somewhat curious that they used MRP vs target boost...

I had been meaning to post a similar analysis after all the playing I've done with Tip-in. I agree with "unrealistic" high Target boost levels on the left side of the table. It seems to make Tip-in work the way we think it should.

Also the higher the RPM, most often the manifold pressure is going to be close to atmospheric and little to no TIE is required.