Removing silencer cone
These instructions are a synthesis of input from several SHOtimes members. One of them has done this on a '90, a '93, and a '95. It seems like it's much easier to do on a 92-95 model than on an 89-91, due to the redesigned marker lamps.
Instructions for '92 - '95 (Hard)
Remove the cone with the help of a floor jack and stands. Always jack the car on level ground. It also helps if the car has cooled. Working on a hot car only makes the procedure more difficult.
Jack up the front after engaging the parking brake and chocking the rear tires. DO NOT attempt to jack the car if you do not have stands. Make sure the stands are in good condition and capable of holding the car. An alternative to jacking is to cut the wheels all the way to the right.
Remove the air box cover. I also disconnect the intake from the manifold. Stuff a rag or something into the manifold cover while doing this operation to prevent anything from getting into the engine.
Remove the air filter. Remove the three hex head bolts holding the airbox to the frame. (Two go straight down and one goes into the frame near the wheel well.)
Remove the two nuts holding the outside box to the frame. Remove the two screws under the wheel well holding the cover in the wheel well.
Pulling on the cover should give you access to the inside of the quarter panel. The outside airbox should come out with a little delicate manuevering.
With the outside box removed you can clearly see the cone inside the box. You can just push the cone out of the outside box. This will require some elbow grease! You now have a larger intake hole in the outside box.
Manuever the outside box back in to the wheel well. Replace the two nuts on to the bolts coming through the fender. Replace the inside air box and reinstall the three hex head bolts. Install the air filter.
Put the box cover back on the box. Remove the rag from the manifold and replace the tube over the opening. Tighten the hose clamp over the manifold tube. Clamp down the box cover.
Replace the two screws in the wheel well cover.
You can easily hear the secondary runners open during acceleration. Some think it is neat to hear the change in the engine sounds. It is not known how much if any this increases the power but it does sound cool. And is one of the easiest modifications to make.
Instructions for '92 - '95 (Easy)
Some have found it easier to just remove the front left turn signal light and slip the cone out there. One member did this on a '92 and the whole process took about ten minutes.
Instructions for '89 - '91
The '90 was harder to do but did not require jacking the car. You had to stick your hand inside the airbox from the engine side and push the cone out of the outside airbox. I can't be sure but I think I had to turn the cone in the box to get it free. That left the cone hanging up inside the front of the car. I disconnected the power steering cooler from the frame. It meant the cooler was still connected to the system but was hanging under the car. With this out moved you could stick your hand up through the front of the car and manuever the cone out. Then rehang the cooler to the frame.
The only problem I have noticed is there will sometimes be some sand in the airbox. I don't know if that is a result of removing the cone or not.
An even easier modification is to add the K N Air Filter (880+ cfm vs. 500 cfm for paper filter). Steve Hazard (the president of the NorthEast SHO Club) says that the airbox can be drilled to allow even better air flow.
Gary Morrell disagrees:
This mod is of questionable performance value. It is reminicent of turning over the air cleaner cover on carbureted motors of yore... The intake noise increased, and loud cars are always faster than quiet cars, right?
Assume for a moment that the outside air temp is 70F and the underhood air temp is 170F. Air density is related by the formula:
doa = square root[(460 + tuh)/(460 + toa)] x duha
doa = density outside air
duha = density underhood air
toa = temperature outside air
tua = temperature underhood air
therefore: doa = square root[(460 + 170)/(460 + 70)] x duha
doa = square root[ 1.19 ] x duha
doa = 1.09duha (well duh...sorry, couldn't resist)
( Note: the 460 in the equation allows the use of degrees F instead of having to convert everything to degrees Kelvin, absolute. )
So, outside air density is 109% of underhood air density, or 9% greater. Because mass air flow increases in direct proportion with density, HP produced with the cooler outside air will increase 9%. Therefore, an engine that produces 200HP with 170F air will produce 218HP with 70F air.
Useful rule-of-thumb: HP changes 1% for every 11 degrees F change in intake air temperature.
Obviously, the effect of drilling holes in the airbox isn't as bad as the calculations suggest, because the majority of the intake air is still coming from the big hole in the fenderwell, but those extra holes in the engine compartment are hurting you, not helping.
The above is precisely why Vadim came up with the cold air can for the conical K N filter/77mm Pro-M mass air sensor combination.
You are solely responsible for any problems or injuries that occur from the actual removal or during operation after removal of the cone