Well this is where it all started.
I always wondered why the air temperature always seemed so high.
I would routinely see temperatures in the low 200s. I always figured
that it was because of my environment of a tightly cowled motor with the
only fresh available pre-heated by the radiator. While at the West
Coast Nationals at Pleasanton a few years back doing my usual gawking at
all the new toys I struck up a conversation with one of the sale persons
at the Edelbrock display. Of coarse it didn't take long before we
were talking about the Pro-Flo EFI. He mentioned that they recently
discovered that the placement of the MAT sensor in the back of the manifold
was a poor choice. A very poor choice. Basically what is happening
is the MAT sensor is measuring the temperature of the aluminum manifold
rather that the air passing through it. He suggested re-locating
up into the air cleaner and that it would most likely reduce the air temperature
reading by 30 degrees. Well the timing was perfect as it was getting
to the end of the rodding season and I was looking for something to fix
during the off season.
Now the problem was where to relocated it. Well there weren't too many places that I could put it that I still could cleanly get the wiring to. About the only suitable location was on the driver side just outside of the throttle linkage. As it turns out that was the the first of several locations. It did make a dramatic difference in the measured air temp. The maximum temperatures were now 50-70 degrees cooler. I needed to readjust the Global Fuel Modifier considerably lower to to bring the fuel map back into the ball park. The 'Blower Roll' effect got better also. Almost could drive it in stop and go traffic, but not quite. After seeing how much of an improvement it did make I started wondering if I could find a better location. I wanted to find the coolest location that would still accurately sense the air temperature going into the air horn. I wasn't sure that the front, middle, or rear of the air cleaner assembly would be the best location so I needed to run some experiments. What I did was locate two more thermocouples inside of the air cleaner. One towards the front and the other near the rear. This gave me three measurement points. After several test drives it looked as if the rear most location was slightly cooler most of the time compared to the front and middle locations. I would have thought that closer to the front was going to be cooler rather than the more restricted rear. I had to modify the MAT sensor so I could re-locate the sensing element (the thermistor) where I needed. So I mounted it in the rear and gave it a try. Slightly better but I still wondered if I could do better. The big problem here was to isolate the sensing element from the radiated and conductive heat sources and only sense air temp. Well the modified sensor did a fair job on the conductive side (still had heat coming up the copper wires to the thermistor but there is no easy way to make this better) but trying to find a place that was far away from the radiated sources with all that chrome and aluminum wasn't going to easy. I next located over the center of the air valve but the proximity to the air valve itself actually made it worse. Well what I finally settled on (at least for the moment) is mounting it in a large PVC cylinder above the air valve. A 6" PVC pipe coupler fit the bill nicely. It fit tightly over the air horn without restricting any air flow. It is about 1" shorter than than the total height of the air cleaner. I was a little concerned that this might restrict air flow but I haven't been able to detect any degradation of performance. So the theory here is that filtered air inside of the air cleaner will all have to flow over the top of this tube into the air valve passing directly across the thermistor. Being it is plastic it won't thermally conduct heat up from the air valve as much as a piece of metal would. Its black so maybe it won't reflect as much heat. In any case I don't think that I can get the thermistor any more isolated from external heat sources and closer into the air stream as this. Of coarse if you can get fresh outside air into the air horn that would be better yet. Also I would be very jealous so don't tell me about it (just kidding, not about being jealous but letting me know....).
Here are some photos of the MAT relocation efforts........