How much space above the gas tank for sub mounting screws?

PNW Mike

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I'm finally far enough along in my stereo project to pick up a powered sub and get it installed, and want to make sure that when I mount it, that I don't run any screws into the gas tank, fuel lines or any harnesses under the car, because that would be "a bad thing". :)

I'd like to mount it on the passenger's side of the trunk, next to spare tire well, as that flat area has enough space for the sub I'm considering and has easy access to the power wiring and RCA cables. I was previously going to use the driver's side, but it turns out that is not a big enough space after the trunk inside trim panels are installed and I don't want to try and build some kind of "creative" mounting bracket for the sub if I can avoid it.

I looked underneath the car on the driver's side as best I could with the car on the ground and without dropping the gas tank, and it seems that there might be an inch or two of space between the tank and the bottom of the truck floor on the passenger's side, but I can't see if there are any hoses or wiring that stick up. It looks like the tank straps hold the tank to the bottom of the spare tire well plus one area at the front of the passenger's side taller area, and other than that, there is an air gap on either side. It does stick up a bit on the passenger's side, but not all the way to the bottom of the trunk floor from what I can see.

I'm going to use the shortest possible screws, just in case, likely 1/4" ones, but that's still enough to cause a problem.

Am I understanding this correctly, or will this end up with a screw going into part of the gas tank, a fuel line, or a harness that I can't see under that area?
 

badass98svt

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I would not put a single screw through the floor of the trunk. Come up with a different way to mount it.
Have a link to the powered sub you plan on buying?
 

ttocs

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we can't really tell you how much space there is or should be because if we are playing a game of fractions of an inch when it is right/wrong. Try to find a bolt/frame rail or something inside the trunk that you can locate on the bottom either by sight or by hand/feeling around and you will see if there is enough space or not. I have mounted a bunch of boxes to the floor of the trunk but the rule when drilling/throwing screws is you have to check what is on the back of the panel your working on. The gas tank is pressed pretty hard against the bottom of the trunk to keep it in place so in some places there is NO room, in others there is a 1/4" or so.

I do remember one system that a former installer for the shop I was at installed in a fox body/hatch that I had to pull out. I will never forget when I went to pull the box out and turned my drill on to remove the mounting screws and the screw just kept growing and growing as it came out. I am not sure where he found 2.5" screws in the shop but he was going to make sure that the box didn't move by successfully mounting it to the tank. As soon as the screw came out the shop smelled like gas...
 
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PNW Mike

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Sub is a Pioneer TS-WX400DA, see https://www.crutchfield.com/p_130TSWX400/Pioneer-TS-WX400DA.html. It's not huge, I'm installing a modest system and i want to keep my spare tire.

Many years ago I drilled into a fuel line while installing an amp under a seat in my first car, and that is an experience I'd like to avoid repeating. I was one small spark from a big problem, and the garage smelled like gas for a long time. As the line was lower than the tank, it siphoned a few gallons out on the floor before I could seal the hole. To the day that car got wrecked about a decade later, that metal fuel line had a piece of rubber fuel line split and clamped over the metal line to seal the hole. I never did get around to a better repair, and it held great despite it being a fuel injected car and that line having something like 50-60psi it in all the time.

I'll take a peek above the tank with a borescope to see what's under the spot I'm considering.
 

badass98svt

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100w RMS. That thing is hardly worth the effort of the install.
On the passengers side, if you lift the carpet up in the trunk you will see a rubber grommet. That hole goes through the frame rail I believe. Maybe you could figure out a way to utilize that hole.
 

ttocs

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as I said the first rule of throwing a new screw in or drilling a hole is to check on the other side. I am proud to say I had drilled countless holes in cars over the years while installing and I have never hit anything that I shouldn't have just because I am a little anal about making sure I have the spot located on both sides.
 
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PNW Mike

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I looked at the area above the gas tank with a borescope today, and as I suspected, there is about 1" to 1.5" of space above the tank on the driver's side next to the spare tire well, at least on my car. With the light on the borescope up there, you can actually see most of that space from underneath the car when you look from various angles. There are a suprising number of gaps to look through to see above the tank, you just don't notice them as the area above the tank is normally very dark.

There are a few areas where the fuel lines look to come within 3/8" to 1/2" of the trunk floor, but that should be plenty of room as long as I use short screws. I'll also try to fit location the sub so no mounting screws are right over the fuel lines if I can. The tank doesn't seem to really protrude much above the rear "frame rails", which equates to only about half way up the depth of the spare tire well, if I measured right. If not, I may be asking questions about a gas tank install or gas line repairs in a week or two... :)

The blue tape in this pic shows the approx area of the "hump" in the gas tank on the passenger's side. The hoses are about 2/3" of the way forward in that space.

1696814158654.png

100w RMS. That thing is hardly worth the effort of the install.

If I didn't already have the interior out to dynamat everything, yes, but I do, so it's not much effort. I had already run power, ground, and a trigger wire for the amp and had preemptively run an extra pair of RCA cables to the trunk for a sub. Figuring out where to mount the sub is ending up being the most involved part of the job.

For this system and the music I listen to, it's a reasonable size. If I was 20 years younger, it would be a much bigger sub and main amp. :) But... what younger me preferred for stereos and exhaust systems is a non-trivial part of why I now have to be careful about the hearing I have left.
 
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PNW Mike

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The sub is mounted where i was hoping to, even better no "oh crap"moments occured. :) If it hadn't decided to pour some of our lovely PNW liquid sunshine late yesterday and this afternoon, I'd already have it wired up and working. Ah, the joys of having to work outside.

I wanted to share my final mounting locations in case someone else reads this thread and wants to try this. If you are thinking about doing this, do it with great care! This was the result of a lot of careful measurement and an hour+ with the borescope and a tape measure looking around and taking notes, and seeing what was where before I decided on a final postion for the sub.

The blue tape is in the same spots as in my previous post, so you can use it as a visual reference. The only all-up picture I took of the installed sub ended up too blurry to be worth posting, unfortunately.

The front mounting screw goes into the space above a small bracket that the tank strap mounts to at the front of the gas tank.
SubMount-Front.jpg

The rear mounting screw goes into the passenger's side "framerail" and can't be seen from below at all.
SubMount-Rear.jpg

This is the bracket that the front sub mounting screw is above, the screw ended up approximately above the red dot, I could only see it by looking up through the circled hole with a borescope, and even then barely. I was able to find the approximate vertical size of that bracket by how much I could push the borescope up that circled hole, which was helpful as a starting point for how much space was above the tank.

Of note for someone else who wants to try this, the fuel lines running left to right in this pic are the closest ones to the floorboard - they bend upwards towards the floorboard on the inside of the framerail. The exhaust pipe is close to the fuel lines where they cross the framerail, but not too bad; the lack of perspective in this picture makes it look a lot closer than it actually is.
SubMount-BottomFrontBracketView.jpg

Here's an idea of the amount of space above the tank, with the fuel lines for a size reference, the lines have a good 1/2" to 3/4" of clearance to the floor, with 1.5" or so total - these pictures are taking look forward by pushing the borescope above the tank using the small gap at the back passenger's corner of the tank. In the back of the second picture on the upper right side you can just make out the vertical face of the bracket the front mounting screw ended up above; the only up close picture I got with the borescope was blurry and not worth sharing. Holding the scope in position and the phone to take a picture while lying on the ground under the car was a challenge. The borescope I have doesn't have a a super high quality camera, but it does the job without costing me an arm and a leg.
SubMount-SpaceAboveGasTank1.jpg

SubMount-SpaceAboveGasTank2.jpg
 

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