In Reply to: The question is though... posted by Jeff J. on October 26, 2001 at 17:09:50:
The SS attempts to match the AFM's voltage curve. It's just trying to act like an AFM. Three of the knobs get the curve to match fairly closely..the fourth allows some adjustment to acceleration enrichment. As an example you can't floor an AFMed s14 at idle without it going lean and coughing a bit. Things like throttle response don't show up on dyno charts but they are very important.
A mapped fuel curve, whether by piggyback or stand alone mgt, can be more precise. Also, it can be derived from additional sensors such as a throttle position sensor. The stock AFM or SS approach never really knows where the throttle is or how fast it is moved. There is a time lag that you cannot avoid without a true TPS. A TPS sensor adds this input so that the load and rate of change of throttle can be known and accomodated more precisely, more of the time. This aids driveability and make the car feel crisper. But even just adding an SS will improve response cuz there is no more door flapping in the breeze. Keeping the Motronic in place with an SS or a piggyback approach retains other nice features such as proven relaibility, saved time, no need to develop other things such as hot and cold start routines and so forth.
>>Any other advantages you can think of with the "piggyback" computer approach over the MAF one? It should also be possible to install a "hot wire" element into another intake (such as a DTM carbon intake) if you wanted to eliminate the stock Plenum and airbox if you were using the split second kit<<
Not exactly. A MAF can't tell which direction the air is moving, and additionaly it can also be fooled by turbulence. With wild cams such as the 308 you mentioned, there are reversion issues to deal with. Some of the air could go through the MAF and then back out again such that it's getting measured twice. That is why SS suggests using the stock airbox. With a throttle position sensor in place you can solve that issue. You can adjust the fueling at any points where reversion causes trouble. Or just use the stock airbox and somewhat mild cams. Without a MAF to worry about, the intake ahead of the plenum can be more effectively tuned too. Also MAFs are not often used on turbo setups - tricky stuff can happen in case if you ever envision going down that path.