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Thread: Testing: 3A92 engine intake performance

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    Administrator Daox's Avatar
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    Testing: 3A92 engine intake performance

    I've been thinking about doing this for a while now. I have sold my MAF sensor housings since before I even owned a Mirage myself. I did the development and testing with the help of you guys here on the forum. BIG thanks guys! However, I've always wanted to know just how much restriction there is in the intake system. Well, there are ways to actually test and measure how restrictive the OE setup is, and from that we can estimate how much power we can gain from going to a less restrictive setup. There is also the factor of intake air temperature that can drastically effect power output as well. As you may know, a bunch of guys use warm air intakes to get better fuel economy. On the other hand, guys looking to eek out more power use cold air intakes. Beyond that, length and diameter of the intake tubing also have effects, as does that resonator box on the OE setup. So, if you are going to do an aftermarket / DIY intake, what is the best way to go about it? There are a lot of variables.

    So, I am thinking about doing some testing on the intake system. I haven't dove in yet, and I really haven't even thought about it a ton yet. I am really wondering if there is interest from you guys in this topic. If there is I'll go ahead. If there isn't, I'll likely move on to something else. So, I need your feedback! If you are interested, make sure to hit that thanks button, or reply with some words.


    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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    Honestly I would be more interested in a phenolic intake spacer.

    and depending on what the throttle body to intake inner diameter mating looks like, possibly a spacer to help with any obstruction as may be there, such as intake being smaller then throttle body diameter or vice versa.

    If found to be adequate material to port out intake for larger throttle body.

    I don't own a Mirage yet, but I would expect better gains then just putting a different air intake from throttle body when the intake manifold and throttle body may be improved for better flow

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    Daox (12-18-2018)

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    Still Plays With Cars Loren's Avatar
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    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/
    Simplify and add lightness.

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    Daox (12-18-2018)

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    And if you really want to get crazy, make a spacer with a spray bar and A N hookups for nitrous use, lol
    50 shot on a 78 hp 3 cylinder, dare to say sub 15 second quarter mile times

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    Loren explained it better than I did, but changing the size of a intake tube would not be worth it in my opinion

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    Loren (12-17-2018)

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    Still Plays With Cars Loren's Avatar
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    Everything is a compromise.

    Larger tube... maybe higher peak HP at 6500 rpm. But, less low-end torque.

    Torque likes velocity. Smaller tube provides velocity and keeps the air moving in the mid-range.

    But, I'm with you. I wouldn't do it. The only thing I intend to do to my intake is feed it some cold air with a BIG duct from the front opening next to the radiator. Leaving the stock intake and piping right where it is... including the cute little bell end... because it's there for a reason.
    Simplify and add lightness.

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    I would also be interested in wide band testing used to see what is the limit of the maf sensor, since there is no viable tuning for the car, I would be interested in seeing what changes to the AFR a larger or smaller maf tube makes if any.

    Generally how a Maf works is a known housing diameter, if you change the diameter of the tube and move more air than the engine thinks you can lose some of the richness that the factory has put in the tuning. May be worth a look.

    I am sure Loren can possibly explain it better than I can. I am horrible at explaining things sometime.

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    Before Aem and emanage became available, we had to get very creative with our tuning the 6g72 Vr4s, and we ran everything from propane injection to safc tuned 650 injectors.
    Lol, propane was kinda scary in Vegas to get in a car and know that in the hatch was a propane tank that sat in the sun for 8 hrs, 110 outside lol, it was nerve racking to say the least.

    Off topic I know, sorry

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    Still Plays With Cars Loren's Avatar
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    I've actually never done any tuning with a MAF. Megasquirt is normally done with MAP, and that's where most of my tuning experience is. But, yeah, I guess if you're getting outside of the "envelope" of what the factory system was tuned for, you could be sending more air past the MAF than it thinks is possible. In that case, the ECU is going to deliver fuel based on what it "thinks" it sees rather than the actual, which is more. That would lean the mixture. And typically OE tuning is crazy rich (like 12:1 or so) at WOT because it's very safe and keeps the engine from blowing itself up. But, a little leaner than that (say 12.8-13.3) can actually deliver a tiny bit more power.

    Cheating stock ECU systems is fun. There are so many different ways to do it!
    Simplify and add lightness.

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    Quote Originally Posted by JMVegas View Post
    Honestly I would be more interested in a phenolic intake spacer.
    Why would you be interested in this?


    and depending on what the throttle body to intake inner diameter mating looks like, possibly a spacer to help with any obstruction as may be there, such as intake being smaller then throttle body diameter or vice versa.

    If found to be adequate material to port out intake for larger throttle body.
    I can certainly check this. I'd imagine that the manifold matches the port, but stranger things have happened.



    I don't own a Mirage yet, but I would expect better gains then just putting a different air intake from throttle body when the intake manifold and throttle body may be improved for better flow
    I honestly don't see any glaringly obvious problem with the intake system as is. However, I have seen testing that shows other OE intake systems that have a restriction that limits power by up to 7.5%. You never know for sure unless you test 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)


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