HAI/WAI questions/numbers
 

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

Hey Jojo, great post.

Off course we want to know how to do this mod.

Can you get fuel consumption (l/h) in group 015 and speed in group 018 in VAG-COM? I know I could on both my A3 and A4, but both were OBD-II.

With logging and using markers in VAG-COM while making a couple of highway runs in a loop using your cruise control, it should be pretty easy to test this. You just plot the fuel consumption lines on a graph after the fact and see which configuration gets the best mpg.

I did that when I tried various IQ, boost and timing mods with my A3.

Mod is super simple, the stock air box has 2 inlets and a flapper valve to switch between them. CAI goes out the front and into the fender well, WAI goes out the back (smaller diameter opening) through the stock warm up hose to the heat shield on the exhaust manifold, which comes stock this way. The flapper valve is controlled by a temperature sensitive vacuum switch (mechanical) which is mounted in the air box itself, vacuum lines connect externally. I simply removed the vacuum feed from the vacuum switch and ran it directly to the flapper, or basically just remove both vacuum hoses from the switch and hook them together, thus eliminating the switch. Now you have manifold vacuum controlling the flapper directly. Strong vacuum equals WAI/HAI and low vacuum opens the flapper for a burst of CAI. Just a quick jab of the throttle makes the flapper move, hard to tell what it does while in motion however, but judging by my numbers I would say I am getting the warm/hot air I was trying to get.

Phase 2 is to find an electrically controled vacuum switch so that I can override this behavior and force it into CAI mode if things heat up too much. Know of any electric/vacuum doo dads that can do this in a A3 Jetta, as I do have a parts car I can steal things from :-) Maybe the charcoal canister purge valve or something, not 100% sure yet, but I am sure there is one in there somewhere I can steal for phase 2 of this mod.

I have a lot less groups available to me being OBDI, but I will check it out to see what data I can log. I don't recall seeing fuel consumption though. I know I can get VSS input and injection pulse width, and I don't care if it is real time display or I just hack away at my log files after the ride to see the mpg numbers at any given point in my ride, you know? I will be doing my logging on my long commute to and from work daily, so same ride to and from with lots of different scenarios along the way. Other than that just about all inputs to the ECU can be logged. Just a matter of figuring out which ones I need to calculate the MPG along the way, you know?

JoJo

Is this a diesel you are doing this on? If so a WAI reduces FE by increasing heat transfered to the block and cooling system.

That is your opinion. A counter argument could be that a WAI increased the burn rate. Or if you increase the injection pressure, you get higher combustion temperature and more heat transfer, yet better BSFC. The point is, I think it helps, you think it doesn't, but none of us have put an engine on a dyno to test it appropriately.

No, not a diesel.

Fortunately this has been well studied. This is on a naturally aspirated engine. See the lower half of page 11 and figure 14 in the appendix.

http://aerade.cranfield.ac.uk/ara/1937/naca-tn-619.pdf

Good.

The 30s technology engine in that paper does not have much in common with recent small diesel engines.

You know, lower rpms also increase heat transfer, yet fuel efficiency often goes up to a point when reducing rpm because there are other variables at play.

The most significant difference between this 1930's engine and a modern smaller diesel engine is the compression ratio. This older engine only had a compression ratio of 14.5:1. Modern diesel engines run a compression ratio of 18:1 to 24:1. The use of the higher compression ratio exacerbates the problem of heat transfer to the walls of the cylinder due to the increase in TDC air temperature.

I have found and posted a scientific and thorough study by a well respected group in regards to the direct correlation of IAT and the efficiency of a diesel. If you can find a more recent study by an equally acclaimed/accredited group using a more modern engine that refutes the results of the report I posted, I would love to read it. All information I can find indicates that the effect of air temperature dwarf all the other variable's effects.

The first 10km, or a warm up time would have to benefit from HAI wouldnt it? Especially in winter?

With my constant pulse and glide I use for a gas engine, its always cooling off.

Just like a thermostat in the cooling system is used to save gas by reducing warm up.

After warm up we still dont know for sure...

A grill block or no grill block would affect real life data too? Just as ambient temperatures, load, car....