CAI mpg debate...my mind is blown
10-10-2012, 10:38 AM
#23
The reason the warm air intake works is simple and unintuitive. Hot air and fuel burns more efficiently. Jet engine manufacturers have known this for a long time and they use it because for them, even tiny amount of fuel efficiency is a huge deal. After the compressor stage in a jet engine, the air passes through a heat exchanger where the post turbine stage exhaust gases are used to heat up the intake air before it goes in the combustor stage. They also pre-heat the fuel in some cases.
I don't feel like explaining why this works because chemistry is not more forte.
I don't feel like explaining why this works because chemistry is not more forte.
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10-10-2012, 10:41 AM
#24
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Smokey's engine supposedly also had trick cams and rods, and had to go through a very nasty warm up period where the motor was subjected to large amounts of part load knock. The engineering behind it seems to be at least plausible to me, but the secrets of actually making it work may have died with Mr. Yunik.
to OP: you will NEVER NEVER make you money back on any fuel efficiency mods except for maybe a good software tune, and then only if you drive alot and keep your foot out of it.
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10-10-2012, 11:34 AM
#27
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I own a 2007 Mazda CX-7. It's AWD, with a 2.3 liter 4 cylinder, intercooled turbo.
I want to do some mods to it to hopefully better the fuel mileage, but because of what I've been reading on the internetz...my mind is blown.
My theory is simple, "remove factory implemented restrictions, and volumetric efficiency should improve."
When I say: "I don't want it to be faster, I want it to have better fuel economy."
I mean: "The increased power due to less restrictions, should also provide better fuel economy."
Same reason that my stock '99 Miata got 26mpg, and now turbo'd and megasquirted it get 29mpg's.
I was thinking about getting a better flowing intake, thinking, "the less restrictive design of the CAI should provide better airflow making it easier for the turbo to move air, which should increase efficiency".
However, I read this, "CAI will end up increasing fuel consumption not decreasing it. Colder air will be metered by the MAF and fuel will be ADDED to keep the ratio right. You'll get more sound and maybe a little more power, but not less fuel."
How is that?? I'm thinking that response means, "since my CAI makes so much noise, I spend more time on the throttle". That's why the fuel economy decreases.
I want to do some mods to it to hopefully better the fuel mileage, but because of what I've been reading on the internetz...my mind is blown.
My theory is simple, "remove factory implemented restrictions, and volumetric efficiency should improve."
When I say: "I don't want it to be faster, I want it to have better fuel economy."
I mean: "The increased power due to less restrictions, should also provide better fuel economy."
Same reason that my stock '99 Miata got 26mpg, and now turbo'd and megasquirted it get 29mpg's.
I was thinking about getting a better flowing intake, thinking, "the less restrictive design of the CAI should provide better airflow making it easier for the turbo to move air, which should increase efficiency".
However, I read this, "CAI will end up increasing fuel consumption not decreasing it. Colder air will be metered by the MAF and fuel will be ADDED to keep the ratio right. You'll get more sound and maybe a little more power, but not less fuel."
How is that?? I'm thinking that response means, "since my CAI makes so much noise, I spend more time on the throttle". That's why the fuel economy decreases.
This is all actually much more complicated than you think it is. I see what you are getting at but there are a great deal more variables at play than air temp, MAF, AFR.
How do you like the CX?
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10-10-2012, 12:13 PM
#28
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It does not matter what physical device is restricting the airflow on the intake side, be it a throttle plate, an air filter, or one of Pusha's extra-narrow fleshlight inserts jammed in the intake tube. If a restriction is being created to airflow which results in a pressure differential, then the engine is having to do the same amount of work to create that pressure differential.
The theory behind this warm-air hypermile concept is to decrease the total pressure differential (between the intake manifold and the outside air) by decreasing the total restriction through the intake system, to which the throttle is one contributor.
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10-10-2012, 12:33 PM
#29
Yeah, I guess that's pretty obvious now that I think about it. The total physical restrictions on the intake system simply affect overall efficiency regardless of where they are or what they look like (absent any secondary effects that I wouldn't pretend to have any working knowledge of).
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10-10-2012, 01:34 PM
#33
I'm not going to get into the science of pumping efficiency, but I'll tell you that it took the companies making mods for the MS6/MS3/CX7 about 4 years to crack the code on the stock ECU in these cars. NOBODY has discovered how to get good mileage out of them without significant sacrifice in power. The motor in your CX7 is identical to my MS6 except you get a smaller turbo. You do not want to **** with the programming in this car if it's your daily driver, you simply cannot get better mileage unless you take the turbo out of the equation. Bolt-ons do nothing for mileage on these engines.
You can do one of a couple things:
Get a Scangauge and use the instant MPG function to monitor how you drive... and keep your foot out of it, and be happy in the low'ish 20's.
or...
Get one of the various piggybacks and turn the boost all the way down, and a scanguage, and be happy in the mid'ish 20's, and zero power.
On the freeway, you can certainly do better, but combined, it's a lost cause with these cars to expect you can do much better than about 25mpg unless you drive like a complete and total bitch.
I drive my MS6 pretty hard and get around 18. On the freeway I try to do 80 and it gets about 21. I'm stoked when I get over 20mpg combined.
You can do one of a couple things:
Get a Scangauge and use the instant MPG function to monitor how you drive... and keep your foot out of it, and be happy in the low'ish 20's.
or...
Get one of the various piggybacks and turn the boost all the way down, and a scanguage, and be happy in the mid'ish 20's, and zero power.
On the freeway, you can certainly do better, but combined, it's a lost cause with these cars to expect you can do much better than about 25mpg unless you drive like a complete and total bitch.
I drive my MS6 pretty hard and get around 18. On the freeway I try to do 80 and it gets about 21. I'm stoked when I get over 20mpg combined.
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10-10-2012, 01:47 PM
#34
I regularly get a nice healthy 45-48mpg if I can tuck in behind a semi with the Elantra.
38mpg without, but that's at 70.
Minus the navi/backup camera and tint all the way around (including Llumar Air Blue 80 on the windshield), the car is not being touched minus 36psi in the tires and synthetic in the oil pan on the next oil change.
New smaller cars rock.
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10-11-2012, 01:02 AM
#37
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NOBODY has discovered how to get good mileage out of them without significant sacrifice in power. The motor in your CX7 is identical to my MS6 except you get a smaller turbo. You do not want to **** with the programming in this car if it's your daily driver, you simply cannot get better mileage unless you take the turbo out of the equation. Bolt-ons do nothing for mileage on these engines.
I, and my wife, ***** foot this thing whenever we drive it. It's not my Miata...I don't need to drive it like a race car or break any laws with it. It gets driven to haul our kid around, and that's about it. We both really like the layout of this vehicle and everything else except for the poor mileage. I floored it 1 time in the 30,000 miles that we've owned it, and I was actually blown away by the amount of power this thing threw down. We drove it from my house to Niagara Falls last year for our Anniversary, and I set the cruise control pretty much the whole way up (roughly 300 miles). It averaged like a little over 20mpg.
I guess questions that I need answered are:
How much boost does the CX-7 make?
How much could I cut the boost that it'll still be driveable and it won't feel like an early 80's VW Rabbit Diesel?
How is the boost on the CX-7 controlled?
I don't want to mess with the factory tune, but limiting the boost shouldn't have any effect on the fueling tables, or do any harm to the engine. Instead of dumping fuel due to boost, it should maintain closer to stioch due to the boost not coming on like it did from the factory. Closer, as in, if boost AFR's on this thing are in the 10's, and stioch is 14.7, then 12-13:1 AFR's should consume less fuel.
Lagunitas + thinking too much about this = ramble.
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