CAIs and Fuel Economy; what's the real truth? - Page 2 - Mazda Forum - Mazda Enthusiast Forums


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  #11  
Old 11-08-2009, 09:33 PM
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no, i read that. maybe you missed my section where i debunked it?
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  #12  
Old 11-09-2009, 05:24 AM
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no, i read that. maybe you missed my section where i debunked it?
Debunked it how? The fact is that ALL cars now sold determine the mass of the air down stream of the throttle body, the means of determining the mass is irrelevant. Why do they do this? Because unless the engine management system knows the mass of the air, then there is no way for it to correctly meter out the fuel, and given that gasoline engines are throttled by air and not by fuel, that is the only way for it to be done.

For the sake of argument, let's assume there is significant restriction in the intake at freeway speeds (something that clearly isn't the case unless the air filter is horrifically clogged). At this speed/engine load it matters not whether the intake is restricting the inbound air or whether the throttle butterfly is doing it, by design there has to be enough restriction to only allow 18.66% of the engine's design maximum of air to enter the intake plenum. If you reduce the restriction in the upstream intake, then you'll have to increase the restriction within the throttle body to generate the requisite amount of power for any given speed. Increase the restriction in the upstream intake and you'll simply have to reduce the restriction in the throttle body. Either way the amount of restriction is identical otherwise too much air will make its way through the throttle body and the engine will develop too much power to maintain the desired speed.

Long story short, there really is no way for you to fool the engine management system, and for any given driving dynamic; take in 14.1 pounds of air, add 1 pound of fuel.
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  #13  
Old 11-09-2009, 11:32 AM
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I have not taken the time to read every word in this thread. And I only clicked and read one link, but from my experience running the Mazdaspeed/AEM CAI on my 3, its not really worth the trouble or the cost.
In one of its last article's in one of its last issues, SCC magazine did a study (I believe I started a thread here about it: https://www.mazdaforum.com/forum/intake-headers-exhaust-38/scc-mag-intake-test-16787/) that pretty much negates any real advantage to a CAI.

My fuel mileage did not change after the CAI install. There is little/no noticeable increase in overall performance, and I did develop a CEL shortly after. I was extremely careful when handling the MAF and Baro sensors, so perhaps it would have happened anyway. I really don't know.

The biggest advantage I can see is the cleaner engine compartment and easier access to things now. Plus, the polished tube (when kept clean) does look cool as hell.
Fortunately for me, I did not buy mine at Mazda prices but instead bought it new/used from a forum member that had 2 different CAIs, this one received as a gift and never used it.

Last edited by virgin1; 11-09-2009 at 11:35 AM.
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Old 11-09-2009, 12:03 PM
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Back to the same argument.

Here is my point; you can always find circumstances to support your theories and opinions. You can also find tons of support for your theory all over the internet. You said in the beginning that you wanted to find the truth, but you are looking at this with serious prejudice, rather than looking at it unbiased. If you continue to look at it from the same point of view, you will never see both sides.

I'm not saying that I am 100% right and you are 100% wrong, I am saying that the truth lies somwhere in between. I know personally that you won't lose mileage with a cai because I have had two p5's now that started stock and I installed intakes on them later. Neither one lost mileage and the white p5 gained mileage with a short ram. I attributed that to the new plugs it got when I did the intake, but that gain should have been cancelled out if that were true.

Mostly what I am trying to do here is spark controversy and make this seem like there is another side to it.
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Old 11-09-2009, 12:39 PM
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Originally Posted by wsoape281 View Post
Here is my point; you can always find circumstances to support your theories and opinions. You can also find tons of support for your theory all over the internet. You said in the beginning that you wanted to find the truth, but you are looking at this with serious prejudice, rather than looking at it unbiased. If you continue to look at it from the same point of view, you will never see both sides.
Hmmm, serious prejudice... Well, so far at least, 100% of the scientific and empirical data that I've come across has indicated that mileage will either remain static (especially in warmer climates), or go down. Until I see some data that was derived within a controlled environment and makes a compelling argument to the contrary, as an engineer I don't see how I can view it any other way. So yeah, I guess you could say I'm biased.

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Originally Posted by wsoape281 View Post
I'm not saying that I am 100% right and you are 100% wrong, I am saying that the truth lies somwhere in between. I know personally that you won't lose mileage with a cai because I have had two p5's now that started stock and I installed intakes on them later. Neither one lost mileage and the white p5 gained mileage with a short ram. I attributed that to the new plugs it got when I did the intake, but that gain should have been cancelled out if that were true.
I don't believe I ever said that fuel economy WILL suffer, rather that it will NOT be improved and it MIGHT suffer (especially when the OAT drops below 40 degrees). If I stated categorically that fuel economy will go down when a CAI is added in place of a factory intake, please accept my apology; that was not my intent.

I should note that I do know of one case where the replacement of the factory intake has yielded verifiable improvements in fuel economy, however, said replacement wasn't technically a CAI. In this one instance, an engineer took an old three-cylinder Geo Metro and retuned the intake for greater peak resonance at freeway speeds. When the test vehicle was placed on a dynamometer and run back-to-back with the factory intake, the BSFC was measurably lower with the test intake in place and with the engine running at whatever RPM equated with freeway speeds on that car. Torque in that particular RPM range went up as well, but not surprisingly, it went down below that point (making a gutless car even more gutless).

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Originally Posted by wsoape281 View Post
Mostly what I am trying to do here is spark controversy and make this seem like there is another side to it.
Fair enough.
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  #16  
Old 11-09-2009, 12:41 PM
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Originally Posted by virgin1 View Post

I have not taken the time to read every word in this thread. And I only clicked and read one link, but from my experience running the Mazdaspeed/AEM CAI on my 3, its not really worth the trouble or the cost.
In one of its last article's in one of its last issues, SCC magazine did a study (I believe I started a thread here about it: https://www.mazdaforum.com/forum/intake-headers-exhaust-38/scc-mag-intake-test-16787/) that pretty much negates any real advantage to a CAI.

My fuel mileage did not change after the CAI install. There is little/no noticeable increase in overall performance, and I did develop a CEL shortly after. I was extremely careful when handling the MAF and Baro sensors, so perhaps it would have happened anyway. I really don't know.

The biggest advantage I can see is the cleaner engine compartment and easier access to things now. Plus, the polished tube (when kept clean) does look cool as hell.
Fortunately for me, I did not buy mine at Mazda prices but instead bought it new/used from a forum member that had 2 different CAIs, this one received as a gift and never used it.
I don't suppose you have a link to that article; I'd love to read it and see the graphs.
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  #17  
Old 11-09-2009, 04:17 PM
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They stopped publishing SCC (Sport Compact Car) shortly after. I had a hard copy subscription to the magazine. Perhaps it could be found? I'll see what I can do after dinner.
It was funny cause it was only a little article in the very back of the zine, not like they were advertising that it was ther at all.
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  #18  
Old 11-09-2009, 05:29 PM
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Well, I'm surprised but here it is, though it may be abbreviated from the article that was actually published.
http://www.modified.com/tech/sccp_09...nch/index.html
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  #19  
Old 11-09-2009, 09:03 PM
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Originally Posted by virgin1 View Post

Well, I'm surprised but here it is, though it may be abbreviated from the article that was actually published.
http://www.modified.com/tech/sccp_09...nch/index.html
Thanks for the link, interesting reading.

After digesting the data, graphs, and text, I have the following thoughts (in no particular order):
  • While extremely interesting (for a geek like me), the test isn't terribly relevant to the discussion at hand due to the fact that A) it was a "full power" test, B) on a turbocharged car, and C) with all of the "street" ECU maps erased.
  • I'm not sure I fully buy their conclusion regarding how the engine developed (slightly more) power due to leaning toward stoichiometric from what they termed "the OEM's super rich conservative tuning". Why? A reasonably rich (even a "super rich") mixture will not affect power output as much as they imply (notice how the power curve is fairly flat when the mixture is enriched from "peak" or near "stoichiometric" http://www.gami.com/img/gamijectors/...nderstandg.gif [Note: Look at the second plot set from the bottom of the chart])
  • I would have loved for them to have measure actual airflow and then compared it to perceived airflow, that would have been extremely educational.
  • Mentioned almost as an afterthought was the fact that the three intakes yielded virtually identical performance numbers up to about the 3500 RPM mark, an engine speed that is most likely well above what that same engine would be turning at say 70 mph in top gear.

Thoughts?
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  #20  
Old 11-09-2009, 10:49 PM
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i have made my case. don't see a whole lot more that can be said.
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