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There is no doubt a warm air mod helps the Honda Insight's mileage. However, the majority of mods I've seen send the duct work around the front of the engine or duct air from the cat under the car requiring long duct work. I decided to try a different approach by using the first cat behind the engine and just below the exhaust manifold.

I was lucky to find 2 pieces from my vintage VW parts bin that work perfectly. The first piece is a 2" by 24" fresh air hose which appears to be made of a dense paper with a metallic inner lining. These are commonly used on VW cars from the 1960s. A VW of this era uses two 12 inch length hoses but I was lucky to find one that I had not cut in half so it remains 24" in length and was the perfect fit. The second piece is a 2" exhaust coupler that attaches the hose to the intake elbow.

I removed the original intake and flipped the intake elbow backwards and positioned the rear under the battery tray so it faces the rear of the engine. I connected the elbow and hose with the exhaust coupler. I ran the 2 inch hose under the batter tray and placed it between the engine block and exhaust manifold behind the first Cat. It stayed in place by itself and needed no attachment point. I placed a zip lock bag secured with a rubber band over the hole for the resonator. This will allow it to be easily removed when outside temps get too hot to allow for cooler air to be pulled in. I monitor it all with a ScanGauge II. I would like to find some caps to use instead of the plastic.

I like this option because it allows better access to the front of the engine so I can easily remove the oil filter from the top.

I've had this mod installed for a little over 6,000 miles and it has shown no problems with placement or movement. The temps here this time of year have varied between low 30s to high 80s and I am seeing Intake Air Temps from 98 to 130. Many feel that 90 degrees is the optimum temp but my car seems to run best when the intake temps are 110-112 with water temps of 193-197.

I'm sure you could prepare some type of enclosure around the first Cat to produce even warmer temps if you are in a colder climate. The temps in January were reaching the low 20s and the intake air temp was rarely exceeding 100 so I decided to stuff some insulation (aluminum foil) around the open sides of the cat which has kept the temperatures more stable around 109-121.

I've attached pictures that I think are self explanatory but feel free to email me should you have any questions.

http://i227.photobucket.com/albums/dd91/atlaw4u/Warm-Air%20Mod/IMG_0750.jpg
http://i227.photobucket.com/albums/dd91/atlaw4u/Warm-Air%20Mod/IMG_0752.jpg
http://i227.photobucket.com/albums/dd91/atlaw4u/Warm-Air%20Mod/IMG_0753.jpg
http://i227.photobucket.com/albums/dd91/atlaw4u/Warm-Air%20Mod/IMG_0757.jpg
http://i227.photobucket.com/albums/dd91/atlaw4u/Warm-Air%20Mod/IMG_0758.jpg
http://i227.photobucket.com/albums/dd91/atlaw4u/Warm-Air%20Mod/IMG_0759.jpg
http://i227.photobucket.com/albums/dd91/atlaw4u/Warm-Air%20Mod/IMG_0761.jpg
http://i227.photobucket.com/albums/dd91/atlaw4u/Warm-Air%20Mod/IMG_0747.jpg
http://i227.photobucket.com/albums/dd91/atlaw4u/Warm-Air%20Mod/IMG_0749.jpg
http://i227.photobucket.com/albums/dd91/atlaw4u/Warm-Air%20Mod/IMG_0760.jpg

Nice work! You've got some nice documenting skills. :) Along with the rear speaker installs this is very instructive.

Thank you!

Thanks RLC, it only takes a few more minutes to take pictures and if it saves someone else some time then it's worth the extra effort on my end.

I'm a little skeptic of the plastic bag, I'd hate to see the results if any of that made it into the engine. A blockage of the hose could put a serious vacuum on that...

Other than that it looks very similar to mine. Nice work!

The plastic bag is a temporary fix but it works fine and is secured quite well. You could use other items to block the hole but that's what I had laying around and I could not wait to test it.

It's been working so well I have not really looked for an alternative but I may take a trip to the hardware store this weekend to seek an alternative. I'm currently averaging 75-85mpg on my 20 mile commute between the office and home with morning temps in the low 30s and evening highs averaging in the high 50s. Before the cold spell I was seeing many days with 90+mpg trips and considering we are talking about Dallas downtown traffic I am quite pleased.

the cap from a bottle of prestone antifreeze fits fine.

Here in Texas it has been cold as usual in February. However, the last three days have been unusually warm with a few thunderstorms and thus, more humid than usual. I recorded some of my best mpg figures in a long time with 3 straight days of 90+ mpg round trip commutes to and from work and my best door to door ever recorded of 108.1 mpg. The car was running so well and staying in lean burn so long I first thought the gauges were malfunctioning.

Unfortunatley, the cold air returned this morning and dropped my door to door commute into down town Dallas to 81mpg. But then again, it's hard to complain about 80+ mpg.

Very nice FE numbers. H

Thanks Harold but those numbers are the exception so that's probably why I was so excited. I'm more often in the range of 70-80mpg for my commute with a current LMPG of 88. However, I am always trying to improve.

Cheers

With spring approaching the warm weather is returning and we all know what that means. I have found an alternative route for my commute to and from work that allows me to get off of the highway for most of the commute but adds 15-20 minutes. My speeds vary from 30-40mph mostly with 10 or more stop lights to contend with. I drive this route so long as I have the time to spare. I am now averaging 90+ MPG for my commute with my best ever to date of 122.2
http://i227.photobucket.com/albums/dd91/atlaw4u/MPG/1222MPG03_2008.jpg

Since this is an older thread, I wanted to give it a bump at the same time I say thanks for the pictures. I'm headed out tomorrow to get me the flexible tubing. Looks a lot like the same tubing I used for my Prius. Thanks again.

I'm looking forward to reading about your results.

It's a very good mod. Once it's below 50°F out, I can really notice the improvement in the LB window that this mod brings. Too bad it takes about five minutes to warm up, and I'm usually at my destination by then.

I got the flex pipe and routed it to the area around the cat. I attached it to the OEM tube coming out of the air box after I removed it and flipped it over. I used a rag to stuff into the hole for now anyway. I'm not too concerned about anything getting into the engine as it would have to pass through the air filter to ever do that. The stock clamp wouldn't fit over the flex-pipe so I just slid the pipe over the original air tube. It isn't a tight fit but it fits well enough that there shouldn't be a problem with cool air getting in. I suspect that there would be as much heat lost to the walls of the tube (probably more actually) than there would be at that connection. Anyway, with a temp in the high 50's, I was seeing IAT's of 110F and as high as 115F. Before the mod, I was seeing temps of 75-80F. My next question is: How high can the IAT get before it starts to have a negative impact on FE. I noticed that I was able to more easily hold instantaneous FE around 125 mpg in the mid 30 mph range without as much drop in speed as before.

I've read on InsightCentral that there's very little mpg advantage above 120°F.

Some folks with Saturns go beyond 200°F IAT, but too hot and you begin to run in to retarded ignition timing that negates the advantage of having more thermal energy in your air charge.