Doc, were gettn off topic here but I will give you my best shot. I don't know how the unit "piggybacs" on so its hard to tell. Does it mask what the pcm sees from the maf to acomplish its job? I would think it has to. OBDI is a completely different animal than OBDII and I figure you know this. The difference between the two has really screwed up dealerships and customers. For instance, on OBDI you read the code, make the repair, clear the codes and drive it to see if the code stays away. On OBDII, you never clear the code. This could get lengthy... I have screwed a service writer with this. When the OBDII pcm sees a code, it logs all readings at the time of the code and stores them in a freeze frame file. What we do now is pull the code and write this freeze frame data down. It gives engine temp, speed, etc. etc. We make the repair and then drive the vehicle under as close to exact conditions as the freeze frame data that we can. Whenever the pcm sees the same conditions as the freeze frame data it remembers "hey, last time I was here there was a problem" so it goes and checks for the problem. If the problem exists it says "yup, I have a problem" and leaves the ses light on. (really, it actually talks to itself, but I think mostly in spanish) If it doesn't see the problem, it says "guess I am all better now" shuts the light off but stores the code and data anyway. As I understand, after seeing the freeze fram data matched 3 times with no further problems it drops the files and all is well. The problem with the dealerships are they still like to clear the codes. Doing this clears the system monitors (system ready) which is what the pcm needs to be able to reason what is sees. Most monitors can be reset with a drive cycle or two. The hardest monitor to reset is the evap. The parameters for this are tight. Tank can't be over 3/4 full or under 1/4. Engine must have something like 120 degree temp. swing. Basically you have like one chance a day at best to get it done. We had a truck at work that was 7 months old that didn't have the monitors reset. The problem with this is that some codes won't set until the monitors are set. I had a Ford Explorer with the SES on. Forgive me for not remembering which code... they call me at the end of the day and tell me it'* ready and they can't duplicate the problem and the light is off. I ask them if they cleared the codes and he said no. I ask them to bring the mechanic out with the scantool. He states the codes weren't cleared. When the screen for system ready comes up not one damn monitor is set. HE CLEARED THE CODES!!!! I explained to them how they were busted and they took very good care of me after that. If you already know all of this then I apologize, if not it gets better. Imagine as on our work truck the monitors don't all set for 7 months and the code you had at the dealer needed them to be set to light the ses again. Will you remember what the code was 7 months ago and understand that'* it'* the same problem or think it'* something new? Even better, will the average customer?

ouch.

1.
try any physics teacher who can draw a free body diagram.
if you're experiencing knock, you're having *additional* forces placed on your pistons, wrist pins, connecting rods, and bearings. any *additional* force will *lower* the life expectancy of your motor. with all due respect, who are they to disagree with that point?
now, how much is purely academic, but since i've said that before:

...

i was hoping by now, I had made it clear (in every single post i've made in this topic, other than getting all sniffly at how much I love this club), that the point isn't whether or not it will kill your engine, but whether or not it is harmful. In my mind (and anyone who can listen to that high school physics teacher), extra force = premature wear.

if you're simply looking for damage, i think i've covered that. as for how much it causes, i think i've covered that too...

Okay. I would agree that opening the exhaust or anything that improves outflow will help because you are reducing the burden on the engine, but any intake modifications to get more into the engine will reduce gas mileage, including running a cold intake, because cold means more dense, and thus, more oxygen. When the computer sees more oxygen, it pumps up the fuel to compensate.

For straight highway, I would bet the majority of improvement was due to the exhaust, and since the difference between outside air and air temp going into the intake are more equal, cold air will not affect gas mileage as much, since high speeds equalizes the differences.

I wanted to wait until I finish my experiment to say more, but here'* what I observed so far.

Since the vast majority of my driving in this car is a short commute to and from work, 7miles for about 20min between cold starts, it is running below optimal temperature for maybe half of that time, since it takes around 10min to fully warm up. If I run a cold intake, it takes longer to warm up, and so burns more fuel to get itself up to the temperature it wants to run at. Because of that, the gas mileage I get is pretty low.

I've tried two intakes on my car so far to prove the point. First I had a 4 in pipe running to the airbox with fiberglass insulation around it, and ran through a tank of 91 octane. I drove the car consistently the whole time, no heavy accelaration, just super smooth light foot. I noticed when running scantool, that air temp was staying pretty low relative to outside air temp, and for a tank, I got 16.5MPG. Also, I noticed when idling for more than 2 min at a stop and up a hill after it was fully warmed up, the water temp would rise over 210.

Second experiment, I ran without any pipe on the airbox input, so it is sucking in hot air all the time. I ran another tank of 91 Octane, and drove exactly the same routine, same route, same exact driving conditions as before, and noticed much higher air intake temps, as expected, but interestingly, the water temp took longer to heat up at idle, and stayed LOWER overall. I believe whats happening is, since air temp is higher, the computer is compensating by reducing fuel burn rate, to keep the overall temperature lower. This was confirmed when I got 16.9MPG, it doesn't sound like a lot, but that is 2.5% improvement in MPG. Of course the engine is continuously compensating for changing conditions, so I would really need to run both conditions for at least two tankfulls, but that takes a long time, so I am trying to follow the trend.

Third experiment, I'm trying 87 octane now with the hot air intake, and I switched from 180 T-stat back to 195 T-stat. I Know, too many changes at once, but I'm getting impatient to do one at a time, and it takes me 3 weeks to run a tank of gas, so that'* where I'm at now.

Now my theory behind all this is, GM is under pressure to get the best gas mileage possible and meet emissions standards to please the government and attract customers, so they designed the PCM to run to a temperature that gives best overall gas mileage and performance and emissions. Of course they also want to appeal to the luxury buyers, so the exhaust needs to be quiet, and in California, no or reduced Cat could cause a smog check fail so that'* not an option.

Now if I were to double my commute distance with the same driving conditions, I would bet my city gas mileage would be better, simply because the engine is fully warmed up a larger percentage of the time. (but that'* not going to happen, I love my short commute )

Will, in your case and even in my case, highway MPG is much better. I have gotten as high as 32MPG on portions of long distance trips so I know it'* possible, and that was with no mods. When on the highway, the engine is fully warmed up and at a steady speed, it is very efficient. I think the streamlined shape of the car also contributes to this.
It'* a matter of inertia. Once the car is in motion, it will require little power to keep it going.

You stated yourself in jest that your city MPG is 0, since you like to WOT it all the time :P.
I'm sure it'* not that bad, but if you did only short trips with the engine only warmed up half the time, I would bet your MPG would be similar to mine, but that would probably not happen because your daily routine is different from mine. I think that'* why some people complain of bad city MPG, while others are getting much better. That makes it very hard to compare.

I do have to say though, by discovering this board, I have learned alot about how these cars really run, and I really apprecicate the frank discussions. I found the board originally, searching for an answer to why my supercharger was making a rattling noise, and now how to improve MPG. Before all my changes, I was averaging around 13 to 14MPG, and now getting 16.9MPG. I don't know where it will end, but I'm happy so far with the improvements.

Can you run two tanks of fuel and get the exact same fuel mileage?

Of course no, but partly in changes to my driving habits, driving route and changes to the car, mainly tune ups and such, I have seen a steady improvement. I'm not going to change my driving routine just to prove a point, so it takes a long time (3 weeks between tanks) to see how these changes help. Once I found the point of diminishing returns, I will try going back to previous mods and run two tanks to see if it is consistent. In essence what I'm doing is fine tuning the car to my own personal driving style, and I think that'* the key. Depending on your driving style and part of the world, some mods could be worse for you, at least that'* how it appears to me.

Even a CAI or intake will increase fuel mileage. Getting more air into the engine allows it run more efficiently. You increase available power, and the engine now doesn't work as hard to maintain a specific RPM level.

Most people who simply drop in a K&N replacement see a slight, but immediate improvement in efficiency. Not to mention added power.

In GENERAL, adding power can increase efficiency IF you keep your foot out of it.

Will,

I respect your opinion and am sure it helped in your situation, but I would challenge you to do a scientific experiment, where you drive only 20mins in city only driving, once in the morning and once at night every day for a full tank of gas, on the same route every day, with a feather foot on the pedal with a cold air intake, then do the same with heat shielding removed so it is a hot air intake, and see how much of a difference to MPG.
You may be surprised at the results. I don't expect you to do it, because that would require changing your daily routine, which is not practical for you, but can you see my point? My point is, I don't race my car or drive highway routinely and use it mainly to go to and from work, and want best efficiency for my situation, which is 50% less than warmed up engine. The faster it warms up, the better, and CAI defeats that.

My experiment isn't finished yet, so I haven't come to a final conclusion, but I'll share it with you when it'* done. Maybe I'll be ultimately proven wrong, but I need to prove it to myself before I concede.

I will tell you this, I removed the snorkel (a 2.5 inch opening) from my airbox, and now have a 4 in opening, and put in a K/N, but saw no improvement in hiway MPG. I wasn't monitoring it before that for city, so I can't comment on that. I also believe CA (california) gas is more heavily oxygenated than other areas, because of CA tougher emissions standards, and that also reduces MPG. When I got 32 MPG it was on a crosscountry trip on non-CA gas. The best I got so far on CA gas was 28.5, and that was with my semi cold air intake with K/N and 180 T-stat.

Green, I'll give you that a HAI is less efficient than a CAI. My point is that my CAI is more efficient than the stock intake setup. And my driving conditions have proved this with the last 5 cars I've owned.

Many of us have had similar experiences. Nearly every car here with a CAI runs more efficiently than they did with the stock airbox setup, including the cars with a stock airbox and K&N replacement filter.

If that'* the case then how can you attribute 4 tenths of a mpg to anything? 3 weeks between tanks is huge. You have no controll over weather or daily traffic to have a test this fine tuned. It seems to me that the more efficient the engine the better. Better emissions, economy, and power. Getting the most hp is usually considered contrary to economy, but I say that'* only if your heavy footed. When you open the engine to it'* full potential and run it light footed you will see the economy increase. I also feel your tieing the pcm'* hands behind its back running these tests with a cold engine. I understand that your after increases for your specific conditions, but it really doesn't prove anything as far as the intake swaps are concerned. No pcm controlled engine runs at it'* optimum cold.

There is nothing scientific that you are asking or doing here. You have so little controll over the test parameters it'* impossible to guage. I hope I am not coming across as an *** here as it truly isn't my intention. I just can't see how your conclusions can be so cut and dried applied the way they are. I need more edimacation.....

Exactly my point.