I have been reading on a Northstar performance site about opening up the air box. This one done to a 4.0L Northstar from an Aurora, and gave an 8 h.p. increase witha K&N filter. Has anyone done anything similar to the GXP'* air box? If so, were the power gains similar?

Here is the link to the site: http://www.caddyinfo.com/dyno/auroraair.htm

I dont think i got 8hp by doing that to mine................

we have the same airbox on my Aurora and your GXP. I gutted it out and noticed a much nicer engine sound. It almost sounds like a turbo. lol. at high RPM'* it has a whistle to it at times.

Stock air box:




It'* pretty restrictive..

My modded airbox:


Below picture shows how I plugged off the airbox resonator.. It made the intake noise much deeper.


aurora with no airbox:



in all gutting out the airbox increased throttle response and passing power. On the 4.6 I am sure it'd be even more of a gain.. It should really liven up your engine! I'd highly recommend it. I still need to do something with my airbox though to smooth the airflow out a bit. the waffled bottom can't be so great for performance. I don't know what to use to fill it in so I can mold the right shape, and it'd harden when it dries. I'd rather not mess with fiberglass..

8 HP, with a proper exhaust mod, netting +18-20 combined bHP. But the GXP exhaust sounds proper already...dont change it

5 tops without an exhaust modification, but the sound will be noticably more whiny!

The first thing I would do to a GXP is rip off the stock mufflers and weld some Dynomax Super Turbos on there. Good thing i didnt get a SSEi afterall, I would have gotten carried away with all the mods there are for them. Ofcourse all the mods are really cool and everything, but I'd have no money.

why in the world would you want to make the GXP sound like crap? I can only assume you have never heard the GXP exhaust.. it sounds so much better than a dynomax muffler!. The GXP exhaust note is just best described as "music" to the ears.

Well no i havent. I mean the 2005 with the 275horse 4.6. Do you have any you can show me? I am too lazy to go Googling right now.

Damn i really wish i could just drop in a 4.6 from an STS. If its possible, I am doing it.

"Turbo" mufflers usually dont flow all that well, theyre probably better than stock, but originally turbo mufflers were designed to increase backpressure on turbocharged cars because of their lack of backpressure....so they arent the flowinest thing out there.

I added Flowmasters to mine the day after I got it and have not regretted it yet, much deeper growl!! I too have gutted my airbox, but not as much as the pics here. I think I am going to do more this weekend. Does anyone know how far the throttle body can be overbored without problems on the GXP'*? I am thinking of doing this next since we have had now help from the experts on this site for more HP from the GXP'*!
Scott