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Thread: Testing: 3A92 engine intake performance

  1. #11
    Administrator Daox's Avatar
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    Quote Originally Posted by Loren View Post
    If you're talking about an intake manifold, the math and logic is similar to that of an exhaust header with the optimal tubing diameter and length being related to the size of the cylinder being filled, and tuning to a particular frequency to optimize for a particular RPM range. For street cars, they're usually going for best low-mid range torque, so the intake manifold runners are as long as practical. The size of the plenum is also calculated in the same manner.

    On the atmosphere side of the throttle body, you primarily just need unrestricted airflow. If you could just open it up right there, with something like a bell to help high-velocity air flow into the throttle body, that would work great! But, the downside of that is that while it would make maximum HP at the high end (great for drag racing... not for much of anything else), it's going to also let a LOT of engine noise OUT through the throttle body. It's pretty obnoxious. Ask me how I know.

    So the purpose of the intake is not only just to supply fresh, clean air to the engine with minimal restriction, it's also to baffle that intake noise, sort of like a muffler. In addition to properly sizing the intake tube and length to aid in airflow, you'll find that there's almost always a "Helmholtz resonator" in the intake tube. That little box that hangs off of the intake tube and looks like a little useless piece of plastic that doesn't need to be there. It's there to help eliminate the resonance in the intake. It greatly reduces the noise, AND... resonance is the enemy of airflow. Whatever frequency/rpm that intake resonates at, there's going to be a dip in the torque curve. So, the resonator eliminates the resonance AND improves the torque curve, eliminating that dip in torque.

    And this is right where the typical "cold air intake" tube leaves you. It's a straight pipe, probably larger diameter than stock, that has done away with the carefully engineered resonator. It MIGHT give you slightly better throttle response at low RPM, and it MIGHT give you slightly more peak horsepower, but it has almost certainly DECREASED torque somewhere in the mid-range.

    It's all about trying to keep that column of air in the intake (and the intake runners, and the exhaust header tubes, and the exhaust) moving forward as efficiently as possible.

    https://www.brighthubengineering.com...ic-efficiency/
    I agree entirely. I also think it would be interesting to see what happens if we remove some of those nice OE bits. Does it really hurt low end, high end, or mid range? Can we sacrifice 3 horsepower on the low end to gain 4 or 5 on the high end? Or, can we sacrifice a few high end to get some more low end grunt? As you said, everything is a compromise. Its unlikely we can find something that improves the entire rpm range. However, I have seen that happen. More likely we can figure out something that works better for how we want the car to perform.

    Case in point, even Mitsubishi revised the intake system for the 2017 model year by adding the 'cold air duct'. Is it worth finding these in scrap yards, or 3d printing my own?

    3A92 engine parts history (changes over the years)




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    Loren (12-18-2018)

  3. #12
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    Doax, why would I be interested in a phenolic intake spacer?

    To help support the cold air intake, again 6g72 and 4g63 intake manifold get heat soak fast, with in 15 mins that manifold can't be touched. So why bother in trying to bring in ambient air just so it gets heated by the intake manifold. The intake manifold has a lot of surface area to heat air.

    A intake spacer helps break up the convection. By adding a thermal barrier the whole intake manifold drops temp, the mating surface is no longer bolted directly to the head. does it produce big gains? Nope. But it does help get rid of heat soak. So it is a support mod that does help.

    On the 6g72 and 4g63 with a simple spacer that lifted the intake off the head you can rest your hand on the intake manifold when with out it you will get burned.

    If my goal is to get cooler air into the engine, running it through a 200 degree manifold defeats the purpose of drawing the air from a cooler area
    So if you are going to change intake piping it makes sense to give it the best chance to actually produce gains.

    Simple test, record the temp across the intake manifold, make a spacer, get 2 gaskets and bolt it back together and see the temp difference

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    Moderator Eggman's Avatar
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    Quote Originally Posted by JMVegas View Post
    Doax, why would I be interested in a phenolic intake spacer?

    To help support the cold air intake, again 6g72 and 4g63 intake manifold get heat soak fast, with in 15 mins that manifold can't be touched. So why bother in trying to bring in ambient air just so it gets heated by the intake manifold. The intake manifold has a lot of surface area to heat air.

    A intake spacer helps break up the convection. By adding a thermal barrier the whole intake manifold drops temp, the mating surface is no longer bolted directly to the head. does it produce big gains? Nope. But it does help get rid of heat soak. So it is a support mod that does help.

    On the 6g72 and 4g63 with a simple spacer that lifted the intake off the head you can rest your hand on the intake manifold when with out it you will get burned.

    If my goal is to get cooler air into the engine, running it through a 200 degree manifold defeats the purpose of drawing the air from a cooler area
    So if you are going to change intake piping it makes sense to give it the best chance to actually produce gains.

    Simple test, record the temp across the intake manifold, make a spacer, get 2 gaskets and bolt it back together and see the temp difference
    The 3A92 intake manifold is made of plastic.

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        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.6 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.5 mpg (Imp)


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    Opps, guess I didn't think about that part, mitsubishi defeated my idea

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    Quote Originally Posted by Loren View Post
    ...
    On the atmosphere side of the throttle body, you primarily just need unrestricted airflow. If you could just open it up right there, with something like a bell to help high-velocity air flow into the throttle body, that would work great! But, the downside of that is that while it would make maximum HP at the high end (great for drag racing... not for much of anything else), it's going to also let a LOT of engine noise OUT through the throttle body. It's pretty obnoxious. Ask me how I know.
    ...
    I am pondering on BMC's CDA if it's a good idea.
    Name:  CDA CAI.jpg
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    Quote Originally Posted by JMVegas View Post
    Doax, why would I be interested in a phenolic intake spacer?

    To help support the cold air intake...
    I am planning to do a throttle body coolant bypass if it would help my CAI.

  7. #16
    Administrator Daox's Avatar
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    Quote Originally Posted by Eggman View Post
    The 3A92 intake manifold is made of plastic.
    Yeah, that is why I asked. Yep, Mitsu has already beat us to the punch on that one.


    Quote Originally Posted by Mitz View Post
    I am pondering on BMC's CDA if it's a good idea.
    Name:  CDA CAI.jpg
Views: 1734
Size:  87.2 KB


    I am planning to do a throttle body coolant bypass if it would help my CAI.

    A less restrictive air filter is only useful if the filter its replacing is a restriction at whatever rpm and load you're using. You'll only ever know this if you test your vacuum at WOT and peak rpm. The fancy inside the filter cone looks great, but does it actually do anything? I have my doubts.



    In any case, there doesn't appear to be much interest in me doing extensive testing. So, I'll probably just do some basic testing to satisfy my own curiosity. I'd at least like to know what kind of vacuum there is at max load and rpm. Testing this should be pretty darn easy too. I'll get into it more when I get to it.
    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)


  8. #17
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    I be apart of testing...


    I pulled the factory 'nose' silencer deal off, gained a ton of tmid/top range power, and 5-6mpg
    2018 mirage ES manual

        __________________________________________

        click to view fuel log View my fuel log 2018 Mirage Es 1.2 manual: 41.6 mpg (US) ... 17.7 km/L ... 5.7 L/100 km ... 50.0 mpg (Imp)


  9. #18
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    Also, if anyone wants that factory 'cold air deflector' deal...ill ship it out for $5
    2018 mirage ES manual

        __________________________________________

        click to view fuel log View my fuel log 2018 Mirage Es 1.2 manual: 41.6 mpg (US) ... 17.7 km/L ... 5.7 L/100 km ... 50.0 mpg (Imp)


  10. #19
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    Quote Originally Posted by Timinator View Post
    I be apart of testing...


    I pulled the factory 'nose' silencer deal off, gained a ton of tmid/top range power, and 5-6mpg
    Are you saying you removed the resonator and gained 6mpg? And power?

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        click to view fuel log View my fuel log 2014 Mirage ES 1.2 automatic: 36.9 mpg (US) ... 15.7 km/L ... 6.4 L/100 km ... 44.3 mpg (Imp)


  11. #20
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    Yes, and its very noticeable. I dont know if I have it in the Garage MPG chart, but there is major dips with it factory, vs no resonator/"cold air" snorkel


    2018 mirage ES manual

        __________________________________________

        click to view fuel log View my fuel log 2018 Mirage Es 1.2 manual: 41.6 mpg (US) ... 17.7 km/L ... 5.7 L/100 km ... 50.0 mpg (Imp)


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