[JoJotheTireMan]

Ok, to start with I did do a search, and just spent 2 days reading all kinds of posts linked from one another all on this subject, but still did not see much in the way of temp figures, well not like mine at least. So I post this in hopes of a little guidance on testing my mod and the resulting fuel economy.

I have modified my stock air box with a simple reroute of a vacuum line, high vacuum equals warm/hot air intake and low vacuum equals cold air intake. The idea here is that if I ever do need to floor it, then it automatically switches back to CAI for the added HP at WOT, as soon as vacuum builds again then flap moves back to WAI. I have an A3 VW Jetta 2.0L if anyone wants to know how to do this free mod, then just ask, it's super simple, but I want to know my results before recomending it or not. Also to note is the airbox has 2 inlets, CAI and WAI, the CAI is a little bit larger diameter opening than the WAI is into the airbox.

OK, I also have a VCDS (VAG-COM) interface for my laptop to view and/or record data from my ECU. Sorry no scangauge as I am OBDI :-( I hope I can either find or figure out a way to log the info I need to calculate the MPG from the data in the log files, anyone have any insight into this aspect?

OK, so my testing the other day. I drive 50 miles each way to work, mostly highway, in MA so we have a decent amount of hills. I do neutral coast (at idle) as much as I can, my tires are set at 45psi, and I keep the speed in check around the 60-70 mph range, any slower would get scary, well around here at least.

So, outside temp when I left in the morning was around 28 and when I got to work was around 29. My IAT (started the car, booted the laptop, so the data starts at about minute 3-4ish) started at around 80F and rose quickly to the range of 100F - 140F, so my WAI/HAI mod definately delivers the warm/hot air. The way home was a bit warmer out say high 30's, and same thing the numbers rise very quickly from a cold startup, and ran in the range of 100F - 150F, with a small max of 160F. I did notice a few things from this long commute each way, as I was watching IAT with my laptop and VAG-Scope. Cruising a steady highway speed kept the temps fairly steady in the 130-150 range. Decel in gear (engine braking and the car does have decel fuel cutout mode) saw the highest numbers and the fastest climbs in numbers. I prefer to neutral coast (at idle not EOC for safety sake and not much of an improvemnt in previous testing vs idle coasting) instead of decel in gear, and neutral coasting saw a slow and steady drop of the IAT numbers, I think this is mainly due to the smaller volume of air pulled into the air box at idle, but my longest coasts are 1 mile +/- 1/4mile and on these I saw as much as a 10 degree drop in IAT. I was a bit worried about idling at a stop, but this also allows the IAT numbers to slowly drop some, about the same as neutral coasting.

I have not yet monitered my ignition advance in relation to this mod, and plan to do so soon.

I have had this hooked up for almost a year now, only ran into bucking issues on the higway once at outside temps of 90+F, so I pulled over, plugged my vacuum line and away I went, no harm no foul, but I wasn't logging any data so I don't know the max IAT before she pulls so much timing it starts misfiring.

I am looking for some input on how high can the IAT get before I run into issues? I saw some tests comparing 50F CAI and 120F WAI, I guees mine falls into the HAI class as on a 30 degree day I saw 160F IAT!

Sorry again for the long post and bringing up the same topic again, but I would like to evaluate the results on my VW and see if it is helping FE or not on my car as I fully understand that all cars will react in their own way.

So far, I have managed to pull off 37.5 mpg (whole tank avg) in the summer and with the WAI/HAI I have managed 35 mpg (whole tank avg) in below freezing temps. Before this mod I was lucky to get 30 mpg all winter long, usually in the 26-28 mpg range, so it appears to work, but I would like to gather more data and figure this out better than the calulate it when you fill up method. Just for compairson's sake my car's EPA rating is 21/29, so I guess I am doing ok so far, but want to find more still.

Almost forgot, I have an associates degree in automotive technology but work in the software industry, just a little background for you.

Thanks again for the time and help. JoJoTheTireMan