It's important to distinguish actual intake flow from measured intake flow. I'm not seeing this distinction being made clearly enough. To make the MAF read higher (i.e. to get a higher "fictional" MAF reading), you make the MAF tube smaller. This does not mean the flow has increased - with a smaller more restrictive tube you get less flow not more, even though the ECU is detecting more as a result of the MAF seeing higher velocity! You can make the ECU detect any g/s number you want from the MAF by varying the intake geometry. But (and this is a big but) this has almost no bearing on the actual g/s flowing into the chambers. The g/s number is based on a MAF calibration that (presumably!) was obtained for a stock intake. Ok so what happens when you make the MAF read higher than actual by making the tube smaller? The base maps and tables will call for increased fueling as would be called for at that actual flow level. Presumably the region of maps we care most about is out of closed loop so there is no trim correction. The stock ECU is known to run rich hindering power production, and a smaller MAF tube makes it run even richer. Marc showed the calculations for how much bias can be induced in the MAF readings by reducing the tube diameter - 33% between 2.75 and 3 inch! Does that translate into running 33% richer at WOT? This would be a good question to address.
My preliminary data collection of AFR and timing with my 3-inch MAF shows AFR's in the mid-12's at WOT (below, published previously in my 2GR test and tune thread), which is exactly what I would shoot for if I were tuning, as this is a "magic number."
Agreed (at least mostly). However, my hypothesis is that actual flow is considerably greater than what we are measuring. Roughly speaking, airflow = hp. So
if our swapped motors are making 25% more power than the motor does in it's stock application, then they ought to be flowing 25% more air. Or at least, that is the general trend I would expect to see. Yet your logging (with cams no less!), shows only 208g/s peak flow, the same as the logs floating around from a stock Highlander. To me, that just doesn't add up. What I am suggesting is that by going to a smaller pipe we would not be making the reading higher than actual, but in fact making it match up with the actual flow.
I disagree that the actual flow will necessarily decrease with the change from 3" pipe to 2.75" pipe. By that I mean, I doubt we are maxing out the flow capability of a 3" pipe, so reducing the diameter doesn't necessarily restrict the flow. Speed it up, yes, but not necessarily restrict it.
Now, the subject of the ideal AFR for power is another topic entirely. Looking at the requested AFR log from Torque, the ECU want's to run 11:1 at the top end, which does seem excessively rich. But what about the lower end of the RPM range? In the facebook post I linked to Gavin said that he reduced the presence of the torque lumps at the 2500-3500 range by changing his intake. Looking at my logs with a 2.75" ID intake, the actual AFR in that RPM range is 14.5:1, and the ECU is requesting 13.7:1. Seems plausible to me that running that lean at WOT could be costing some torque. See post #150 of my swap thread:
http://www.mr2oc.com/188-v6-mr2-forum/650833-my-2gr-fe-swap-thread-3.html
The ultimate arbiter of this question would be in my opinion back-to-back testing on the dyno with various intake geometries - not just WOT runs but constant load runs to explore the entire load vs. rpm map. While the calibration of MAF as suggested in this thread should be informative, I don't know how it translates into practical results. I believe the questions raised about the MAF are more directly addressed on the dyno. As I've said before I wish I were in a position to do this kind of testing, but I'm not.
One thing I found illuminating in the Lotustalk discussion (850 posts very little of it with any real relevance) of the intake is the effect of the tube length. Marc has pointed previously to the effect of the harmonics and these I believe are determined primarily by length (along with other factors). It never occurred to me before that harmonics could induce higher than 100% VE (this was pointed out by Marc in analysis of the torque curve). I see that BOE has settled on a short intake tube design. Presumably this is based on their dyno testing. I'm also looking closely at the pic and it looks like the 45-degree silicone bend may be a reducer from the 3-inch throttle body to a smaller tube diameter - hard to tell on this one. I wonder if anyone has access to one of these units to make measurements.
I am thinking about taking my car back to the dyno with the smaller intake pipe to see if there is any difference. I wish I had logged AFR the first time, but at least I can do that on the street.
I still need to go read the Lotustalk threads...
Another factor in play here is the ACIS. When this thing comes on it gives a real kick in the butt and the MAF readings should just jump right there. So just thinking about this now it occurred to me here that I should be looking more closely at my MAF vs RPM data logs. Why this didn't occur to me sooner (and why none of you learned gents suggested it).... let's not go there LOLOL.
In theory if something like the ACIS is tuned right, there shouldn't be a jump when it switches. It should switch at the point where it becomes better to have it open. If there is a jump in power / flow when it switches, that probably means it is switching over too late. Personally I have not noticed when it switches on my motor, but your cams could very well change the optimal switch point.
So.... there is visibly a restriction on my airflow that manifests at the very top end of the range - see how it flattens out. My working hypothesis is it's due to a. tube length, or b. air filter, or c. exhaust? I've changed air filter since then and immediately felt a change on the butt dyno. No measurements yet to confirm. Intake tube length should be easy to change and I intend to. Of course this could be due to other factors. We shall find out with more data.
This could also be cams, valve size, etc. Granted you have the larger cams, but you are also revving an extra 1000 RPM higher than the rest of us and the limit of those larger cams has to show up at some point.