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Old 09-18-2011, 09:00 AM   #1 (permalink)
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warm air V. cold air intakes

how comes warm air intakes are listed as an ecomod but not cold air? Don't both strategies increase Fuel Economy?

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Old 09-18-2011, 09:36 AM   #2 (permalink)
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Originally Posted by MPGranger View Post
how comes warm air intakes are listed as an ecomod but not cold air? Don't both strategies increase Fuel Economy?
Depends on the car, its sensors, driving technique, and the design of the intake--seems to me. My WAI works. I have long wondered about a CAI. I think one reason for the WAI in colder climes is for warm up and for dealing with denser colder air of winter. I would think a CAI would work for accelerating with load as long as you were also using EOC to reap the benefit of the shorter pulse through a longer glide.
See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.

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Old 09-18-2011, 01:59 PM   #3 (permalink)
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PLEASE, search.

there are dozens of threads about this EXACT topic.
MetroMPG: "Get the MPG gauge - it turns driving into a fuel & money saving game."

First: ScangaugeII

Second: Grille Block

Third: Full underbelly pan

Fourth: rear skirts and 30.4mpg on trip!
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Old 09-18-2011, 03:23 PM   #4 (permalink)
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Its all about being able to hit a target temperature and pressure.
In a spark ignition engine you want to get your air fuel mixture as hot and under as much pressure as possible before lighting it with the spark plug.
If you get the air too hot the air fuel mixture could preignite and that would hurt fuel fuel economy and power.
Most vehicles in factory form stay well below that temperature and pressure preignition threshold.
This is one of those mods you really want to A-B-A test to make sure you dont hurt fuel economy.

The next gasoline engine I build I will get the temperature and compression into that ideal range by raising the compression ratio up to about 12:1, using a cold air intake.

A diesel engine is a little different. You always want a cold air intake, the diesels seem to respond best to cramming as much gaseous mass into the cylinder as possible. That is why deleting the EGR and running water mist injection works so well.
1984 chevy suburban, custom made 6.5L diesel turbocharged with a Garrett T76 and Holset HE351VE, 22:1 compression 13psi of intercooled boost.
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Old 09-18-2011, 06:08 PM   #5 (permalink)
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It also depends on temperatures of the engine and outside.
If your engine is getting so warm that it is reducing timing or feeding extra fuel in order to decrease temperatures, then you would be better off with a CAI. This would be the case if it's 90* outside and you have a full grill block.

If it's 40* outside and you have no blocks... a HAI is obviously the choice. Faster warmups will be key here.

REALLY IMPORTANT!!!!! The best improvement in BOTH cases is simply correct construction. There are calculators out there on the interwebs that can help you calculate correct length and diameters of your intake. If this is done correctly, you can worry about having it be a HAI/CAI after that.

Also... What I do, since here in Chicago areas, we have -20 in winter and 120 in summer, I simply made a shield (currently under development and testing) to block or allow engine heat. I also made it so it keeps my engine computer cool in all conditions since it's near the intake that I have made.

So far.... seems that a combination is the best solution for me. My truck gets too hot in the summer, and since I tow often enough, a HAI is just not an option during the summer.

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