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Air box Mod for 98 and 99 seville


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Mark Gogots writes:

For all '98-'99 STS owners, I have found an easy "free" mod you can do to really help your Northstar breath better. It takes about 30 minutes with common hand tools. If you installed a K&N filter, this mod will help even more.

If you take your air filter out, you will notice a hole at the bottom of the air box. Believe it or not, this hole goes down to a "black box" that is COMPLETELY sealed. Go figure!? Not much fresh air coming through there. Go under the car, just in front of the driver's side front tire. Pull back the plastic liner that covers the bottom. Be careful when pulling out the plastic plug clips - there are two at the bottom front of the front tire's wheel well. Those should be the only ones you will need to snap off. Carefully pull back the liner. Once that liner is pulled back, you will see the "black box". Cut the bottom of the box out. I drilled a few holes first,

then used a hack saw blade and easily cut through the plastic. Sand the edges down smoothly. Once the bottom is removed, you will see the hole which leads up to the air filter. Finally, cut an approx. 8" x 6" hole out of the plastic liner directly under the box. GM was nice enough to give you an indentation to use as a template. Make the hole just large enough to allow the air to get up into the black box. Again, sand

the edges down smoothly. Carefully pull the liner back into position. Clip the two plastic clips back into place and you're ready to go! Optionally, I also removed the metal screen located in the throttle body to help further increase air flow

into the runners. But it's up to you if you want to do that.

Net result is that the throttle response is MUCH better and the Northstar really sucks some cool fresh air now. Also there is a great sound when you

punch the gas - but not overly loud or annoying. Good luck.


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OH MY GOSH!!!!!! WHAT HAVE YOU DONE?!?!?! You have ruined the OEM performance of your vehicle! Undo that modification at once, or you will be ridiculed and harrassed by various members of the board. Didn't they tell you that your car is at is fastest possible performance in stock OEM trim? If you haven't been told, your vehicle will now be slower and start having a steady stream of electrical drivability issues, due to your screwing with good stock OEM computer settings. Also, your car will now be ingesting large amounts of water through the hole you created...when you go driving through rivers and streams or drive down that next flooded street! I'm surprised you haven't been notified that what you have done has actually slowed down your vehicle! And even if you run tests and write they state differently (the car actually got faster), you will be ridiculed and tormented by various members. It may be a good idea to keep your good find to yourself. If you choose to stay OEM/stock, then this is a great place. If not, beware!

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I have heard from people who did this - see http://caddyinfo.netgetgoing.com/performancereports.htm -- with apparently good results.


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JTCaddy, yeah, that's a common mod on the '98+ cars. Be careful to make sure all the edges are sanded completely smooth though. And it wouldn't be a bad idea to try to remove anything you've cut on, and wash it thoroughly in soapy water, to make sure you removed all the "burrs". I cut a few of the interior "baffles" out of my airbox on my '97 (a different design from yours) and even though I was careful to get all the plastic shavings out of there, a few still made their way and got stuck in the MAF screen. After I cleaned the screen out, I didn't see any more of them, but I just wanted to point that out so maybe you won't have the same thing happen. Good luck!

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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I dont get it.

On 2-9-04 in another post matlock said " If you want to modify, forget the cadillac northstar in a production car.  You may just wreck it & get frustrated."

Why the animosity?

It's a juvinile game he wants to play. IMO, Don't waste your time wondering, or the boards resources responding.

'93 STS.. opened, dropped, wide...fast.

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"...this hole goes down to a "black box" that is COMPLETELY sealed."

I'm not quite sure what you are talking about. If the air filter were connected to a box that was completely sealed, the engine would not run, period.

I think you may be referring to the plastic air ducting that routes cool, dry air from in front of the radiator support (right next to the headlight), to the air filter box.

If that is the case, you may have created a potential for "sucking" up water directly into your intake if you get into a situation like high water during street flooding, which would be disastrous to your engine.

I have a 93' STS and that is the way the air is routed on mine, but I am not sure if your 98 is the same. It would be worth checking to avoid damage to your engine.


Drive'em like you own 'em. - ....................04 DTS............................


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Its sound like an easy job (maybe too easy) but easy none the less. If it truely is sealed then that would certainly help plus it should still be pretty safe from water intrusion. And MATLOCK, if you see this, stop being such an *smurf*! It's not your place to critique every single thing that someone tries. You left messages on posts that I and other people have started regarding performance mods for the northstar. If you wants to keep your car stock, more power to ya' but that dosn't give you the right to threaten others with the possibility of ridicule or harassment. That is just uncalled for. So if you see this (and I hope you do) knock it off cause' no one wants to here it. Thanks. :P

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