98 STS airbox mod?
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Northstar Engines and System Technical Discussion Discussion, 98 STS airbox mod? in Cadillac Engine Technical Discussion; Well I want to mod my airbox and put in a K&N filter. I tried the other day and it ...
  1. #1
    speedyman_2's Avatar
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    98 STS airbox mod?

    Well I want to mod my airbox and put in a K&N filter. I tried the other day and it was pretty simple to remove the upper portion of it. But there is another piece under it that curves down and then back up. I dunno how many of you have seen this, but I can't get that lower part off. It's stuck in there pretty good. Seems like I would have to remove the bumper cover to access the bolt that holds it in. ANyone know how to get this thing out??

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    speedyman_2's Avatar
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    Re: 98 STS airbox mod?

    Here it is, I got it out. Or My friend got it out. It needed a little muscle.



    Sounds way better and has way better throttle response.

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    Ranger's Avatar
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    Re: 98 STS airbox mod?

    It may sound better, but any perceived improvment is just that. The OEM filter will flow all the air that the Northstar needs or will require, even at WOT.

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    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: 98 STS airbox mod?

    Wanna see how much DIRT a K&N will flow?



    Stock air filter - 0.4 grams. K&N - 7 grams. That's 1,750% more DIRT going into your engine. Air filters are supposed to filter the air... right? Might want to tell K&N that.

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    lry99eldo is offline Cadillac Owners Fanatic
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    Re: 98 STS airbox mod?

    One more time..........you'll get nothing out of this bolt on and that odd shaped hole in the plenum box, is meant to cool the unit under it as well as stabilize air intake temperature and flow characteristics. You may even loose a mile or two per gallon. Congratulations, you've spent money and time for 0 gain.
    lry99eldo

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    Re: 98 STS airbox mod?

    i did not install a k&n filter. i said i would like too. all i did was remove that big ass piece of plastic. to improve airflow.

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    Re: 98 STS airbox mod?

    If the "big assed piece of plastic" you are talking about is what I think it is, that routes intake air over the PCM to cool it. I would be very hesitant to re-engineer something like that at the possible cost of a new PCM. PCM's are not cheap. The perceived gain may not be worth the evenual cost unless you believe that the engineers who desingned it were clueless.

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    mcowden is offline Cadillac Owners Connoisseur
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    Re: 98 STS airbox mod?

    Quote Originally Posted by Ranger
    If the "big assed piece of plastic" you are talking about is what I think it is, that routes intake air over the PCM to cool it. I would be very hesitant to re-engineer something like that at the possible cost of a new PCM. PCM's are not cheap. The perceived gain may not be worth the evenual cost unless you believe that the engineers who desingned it were clueless.
    In the bad old days of American automotive engineering, allowing a piece of plastic to choke off power and fuel economy would probably go unnoticed. Today, I just don't believe anybody is going to let a piece of plastic or an air filter rob the car of horsepower or fuel economy. The car's power and fuel economy are selling points. Why would they cheat themselves out of 10 horsepower by putting in a restrictive air box or air filter, especially when there is so much more competition out there? I just don't see that happening, and I'm not about to put the PCM at risk for heat-related failures to get what so far nobody has proven is even possible. On a Civic, you might be able to get another 50 horsepower with a Type R badge and a K & N sticker if you ask anybody who sells or installs aftermarket ricer parts for a living. The same thing doesn't work with a Northstar.

    I'm not saying you shouldn't do whatever you want to your car, but don't let anybody tell you it's going to give you any benefits unless they can prove it on a dyno. My guess is that, in reality, there will be very little or no measurable difference at all. If you want to prove it to yourself, take the whole airbox out, filter and all, and see how well it performs. Then there's no restriction at all. Then put the whole thing back in and check it. Post the dyno and track results and prove us all wrong. I'm not going to hold my breath.
    Mike

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    Re: 98 STS airbox mod?

    Quote Originally Posted by Ranger
    If the "big assed piece of plastic" you are talking about is what I think it is, that routes intake air over the PCM to cool it. I would be very hesitant to re-engineer something like that at the possible cost of a new PCM. PCM's are not cheap. The perceived gain may not be worth the evenual cost unless you believe that the engineers who desingned it were clueless.
    No, this piece is below that. The PCM is still in its original location. Air will still flow over it the same way it did before. This lower piece is pretty much there for silencing. Which it did a good job at. As fas as me getting anymore HP from removing it, I doubt it. Throttle responsed improved. And the sound is nice. I'm still not done with this though. I'm going to try to connect more tubing and route it to some colder air. Maybe even somewhat of a ram air if I can get a good location. I'd have to seal the rest of the box because the part that contains the PCM isn't fully sealed. I'm sure I can at least pick up a little more throttle response and maybe a few HP with this. I'm also going to be modding my other throttle body I have laying around.

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    Re: 98 STS airbox mod?

    That large chamber at the bottom of that U-Joint looks like it was designed to capture any water that may make it's way to the opening of the intake, and prevent is from reaching the airbox or engine. It also probably helps to reduce induction noise like the large plenum attached to the hose that leads from the airbox to the MAF. Removing that section hasn't done anything but provided and easier path for water to reach the airbox.

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    Re: 98 STS airbox mod?

    Quote Originally Posted by danbuc
    That large chamber at the bottom of that U-Joint looks like it was designed to capture any water that may make it's way to the opening of the intake, and prevent is from reaching the airbox or engine. It also probably helps to reduce induction noise like the large plenum attached to the hose that leads from the airbox to the MAF. Removing that section hasn't done anything but provided and easier path for water to reach the airbox.
    True. But I'm in So Cal. I can't remember the last time I saw water other than the ocean.

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    Re: 98 STS airbox mod?

    Oh well...being in California you really have nothing to worry about then.

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    tremor12 is offline Cadillac Owners Fanatic
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    Re: 98 STS airbox mod?

    Quote Originally Posted by danbuc
    That large chamber at the bottom of that U-Joint looks like it was designed to capture any water that may make it's way to the opening of the intake, and prevent is from reaching the airbox or engine. It also probably helps to reduce induction noise like the large plenum attached to the hose that leads from the airbox to the MAF. Removing that section hasn't done anything but provided and easier path for water to reach the airbox.
    It has absolutely nothing to do with water. It is simply a resonance chamber meant to tune out specific frequencies. Removing that section and replacing with a duct from underneath, along with a heat shield that keeps engine heat from the filter will do nothing but good. I've done this on both and Aurura and a STS and there are gains to be had by opening up the intake...

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    Re: 98 STS airbox mod?

    I guess you missed it, but the second have of that post I made was about reducing induction noise. If removing that piece is going to make that much of a difference, than removing the resonance chamber attached to the hose between the airbox and the intake manifold should also increase performance as well. It doesn't though, and there a good reason for it. Just removing that section of tubing isn't going to do much, since it is not a restriction. If it was, it wouldn't be on the car in the first place.

    Also, what do you mean heat shield to keep hot air away from the filter? Are you suggesting an open element filter assembly underneath the hood? Even with a heat shield, any kind of cone filter, is probably not going to flow properly, and will most likely mess with the MAF signal. A simple piece of duct work leading fomr the whole beneath the airbox, to the front of the car doesn't make much sense, since that's what that tube in the picture is used for. It was obviously designed for a reason, which is why it's on the car.

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    mcowden is offline Cadillac Owners Connoisseur
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    Re: 98 STS airbox mod?

    Quote Originally Posted by tremor12
    It has absolutely nothing to do with water. It is simply a resonance chamber meant to tune out specific frequencies. Removing that section and replacing with a duct from underneath, along with a heat shield that keeps engine heat from the filter will do nothing but good. I've done this on both and Aurura and a STS and there are gains to be had by opening up the intake...
    What are the gains, and what are the pitfalls? There has never been a good, real-world comparison done. The evidence seems to point to few or no gains from modifying the stock airbox and hoses, and possible PCM damage by reducing airflow. Whatever the purpose of the airbox, how much does it restrict air flow? It doesn't look like it interferes at all.

    Again, you can easily test it for yourself by removing the intake hose completely and running with no filter. Then there is zero restriction. Don't run it for long like that, but in a relatively short time you can tell exactly what gains are to be had by "opening up the intake."
    Mike

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