Hi everyone! I'm new to the CEG Forum section. My name is Christian Allen. I own a 98 black SVT and have spent the last year working on a competition stereo.
In my trunk I have an elaborate setup with 3 JL audio 12W6's wired in a series/parallel combination to a 4 ohm load @1500W mono. My latest SPL readings after my last tweaks was 156.0 I'm almost positive I could go higher but I think I might hurt my car somehow. I have some answers for your vibration problems.
1. That "farting" sound was extremely embarrising to me too. After much investigation I discovered 4 ventilation holes, 2 per side behind the rear bumper/air skirt. Just behind the rear tire, reach up underneath the air skirt...way up there (you may need to jack up your car) and you'll feel 2 plastic vents with louvers on them. They will be about 3 inches tall and 5 inches wide. Behind these louvers is a VERY thin piece of rubber. This rubber acts as a one-way check valve for air, kinda like a half-face respirator. I tried to rip the rubber off from the outside but I couldn't get enough grip. I decided to take the whole back bumper off to gain better access to it...what a pain in the butt. After some frustration with the bumper I deciced to reach up there again to try to get the rubber out. I accidently ripped the entire piece of plastic off, rubber and all. At first I thought I had broken something, then after I looked at it I realized it was just snapped on to the frame anyway. So I proceded to "unsnap" the other 3 off and PRESTO! It worked and I was extremely happy. Originally I didn't know these were there when I had the whole trunk stripped during the install. I have repeatably checked the trunk for water leaks and have fornd none. I will seal them up this spring when I redo the trunk...design change, pain in the butt sometimes but fun.
2. Also there is another place you might want to fix too. Under the car directly in the center of the bottom of the spare tire well is a box with black wire loom going into in (no i don't know what it is) that resides on the car with 4 bolts. This thing rattles alot too. To fix it first loosen the bolts, do not remove, just loosen, then slide off. It's kinda like the back of something you would hang on a wall...Big hole to a smaller one. Just tightening the bolts won't do it. I experimented with all kinds of materials trying to get it to not vibrate. The best thing I found to do is place a 4x4" square of MDF (Medium Density Fiberboard) between the spare tire well and the box, place the box back on and tighten up the bolts. No more vibration.
For the most part I agree with Honkeytonk_monkey but I prefer Dynomat or a similar material to vibration dampening versus foam, although in some situations foam will work better.
I also dynomatted my entire trunk. it did make a big difference, but the subs really do not hit harder there is just less vibration and other ambient noise so you get more enjoyment from your subs. Also the definetly place you subs facing towards the rear of the car. This creates a 3 DB increase...in laymens terms it's three times as loud this way!! Oh one more idea go to NAPA autoparts and ask for a body filler, not bondo but a foam spray that fills voids between your unibody gaps. This is HUGE!!! I did it to my hole trunk lid and holy cow did that make a huge difference. After some research I found that most race cars use this same stuff to make there car handle better. They spray it throughout the whole car to make the body stiffer. The stiffer the body, the better you handle. This Spring I will do the same thing. DO NOT, I REPEAT, DO NOT go to a harware store and use a home foam like "Great Stuff" This WILL NOT DRY because in the voids between the body don't get enough air, so you'll have a mess of sticky crap in your car with crappy results.
Anymore questions, just ask. I have totally gutting out my SVT and know all kinds of little tricks and problems and how to solve them through my own errors or problems
Christian 98 SVT
