alessandromeyer wrote:Does anyone have a copy of the 77e21.info site? unfortunately the site was taken down and its linked on so many topics concerning ITBs. There must be something worthwhile on it...
You can use web.archive.org
to find some of the pages. However, the same info is out there on other sites in different forms if you go searching. One simple description of Alpha-N versus SD is here: SD vs AN
alessandromeyer wrote: Is it "just" a simple switching to TPS at higher RPM?
After reading the differences, you can see there are several ways to combine or blend Alpha-N and SD, including a "blended version, where the MAP is permitted to influence the A-N fueling. Note a switching scheme would usually be from A-N (TPS) at lower rpm, to SD (MAP) at higher speeds. A-N is a relatively "blind" system, and simply gives the engine what it thinks it should
have at that particular rpm and TPS—right or wrong—and why it can give smoother (though less accurate) results.
Another interesting note is that, along with the generally over-rich fueling needed to avoid lean spots raising MAP, idle speed control using the ITBs (throttle stop) appears to cause much of the high MAP at idle. When separate idle air bleeds were used with a single IAC, the idle MAP vacuum increased substantially, giving much better tuning control. I can't find the site right now, but simply adding a small plenum behind the ITBs also worked to provide much better MAP and wider range for tuning, much like a standard MPFI car engine. There are ways to handle ITBs without special "load" coding just for them, though it can make tuning simpler for some.