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Thread: Engine air intake temperature

  1. #1
    Administrator Daox's Avatar
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    Engine air intake temperature

    I was messing around with my scangauge the other day while driving to work and I pulled up the intake air temperature gauge. I noticed that on my commute I was seeing intake air temps around 18-20F higher than ambient. As I slowed down for towns, it would raise a few more degrees to about 23F higher than ambient.

    This intrigued me as intake air temperature can have pretty significant effects on power output and also fuel economy. So, on the way home yesterday, I kept the intake air temperature gauge up and watched it as I drove. It was pretty steady and very close to ambient until the engine coolant reached temperatures near the thermostat opening. As the engine maintained that thermostat regulated temperature, the intake air temperature continued to rise until it again was hovering about 20F warmer than what it started at. My theory is the radiator was warming up as the engine opened up the thermostat more and more to keep its temperature regulated. This of course warmed up the air in the engine bay, and the intake is in the engine bay.

    Now, I am running a full lower grill block (pictured below). So, I know that that will probably raise the intake temperatures because there is less air flow through the engine bay to keep temperatures down.





    However, it does make me wonder how warm that engine bay gets without a grill block on it. In the past I would have said its not important and that once you get going there is enough air flow through the engine bay for it not to matter. However, upon seeing the sensor data from my scangauge yesterday, I am wanting to investigate a bit more. It makes me think that Mitsubishi may have really been on to something by adding the intake duct thingy on the 2017 models. That may have had a significant hand in boosting the power output those few hp.





    So, now I am wondering if I didn't have the grill block, what would my intake air temperature be? If someone has a gauge that can measure intake air temp and does not have a grill block, I would love to hear what you are seeing for air temps.


    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing, Rear sway bar, Upper grill block

    Current project: DIY Nitrous oxide setup for ~$100

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        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 47.2 mpg (US) ... 20.1 km/L ... 5.0 L/100 km ... 56.7 mpg (Imp)


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  3. #2
    Still Plays With Cars Loren's Avatar
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    General hypermiler wisdom is that warm air is better for fuel economy. I think this is because the fuel mixes with the warm air better for better atomization. Mitsubishi may have solved that problem with their "micro droplet" injectors, and the fact that they're injecting a really small amount of fuel, anyway.

    General performance wisdome is that COOL air is better for power. (and what's making more power is giving you more motivation from each bit of fuel that you burn) Because cool air is more dense. You get more air in the cylinder without having to resort to forced induction.

    I would think that, especially since Mitsubishi directed cool air to the intake claiming it was for better economy, a cold air intake would be the best thing for a Mirage.
    Simplify and add lightness.

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    Administrator Daox's Avatar
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    Exactly Loren.

    My reading that I've done on the subject says that a 5F change in intake temperature has a roughly 1% effect on power output. So, if the OE air intake is running +20F from ambient, we are loosing 4% or 3hp to warmer air. This is pretty significant, and makes that little 2017 air duct look like a great little mod.

    On the fuel economy side, I know some of the guys running WAI are getting intake temperatures of +100F from ambient. This means they're reducing their power output by 20%! This is great for fuel economy (as long as the ECU isn't pulling ignition timing due to pinging) because it reduces pumping losses by a good amount.

    So, I'd like to do some more testing. If anyone can help and get me some intake temps without a grill block that would be great. Otherwise, I'll remove mine and see what kind of temps I actually see driving at different speeds.
    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing, Rear sway bar, Upper grill block

    Current project: DIY Nitrous oxide setup for ~$100

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 47.2 mpg (US) ... 20.1 km/L ... 5.0 L/100 km ... 56.7 mpg (Imp)


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    Still Plays With Cars Loren's Avatar
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    Ah, I forgot about pumping losses. That's a thing, too.

    My solution for cold air, which I had temporarily implemented, and then removed, was to remove the little panel in the bottom grill opening (I guess it's open for CVT cars for more airflow?) and put a 3" diameter hose there routed up to the stock intake opening. I wasn't planning to seal it off (for a ram-air effect), just a means to get a bunch of cooler air up to the intake.

    Of course, that flies in the face of "grill block" aero technology. I suppose you could do both, though. Block part of the grill... but, leave a good ducted intake opening.
    Simplify and add lightness.

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    Daox,
    . . . . I am seeing 15 degrees above ambient and I don't have an air block. I would like to direct ram air to my intake. Poor man's turbo.
    GOD Bless and Thanks,
    rich!



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