# False Floor/Amp Rack for BMW M3.



## dummptyhummpty (Feb 4, 2006)

I spent a good part of today working on a false floor/amp rack for my M3. I didn't get much done physically, but I think I have most of the layout thought out. Since, I've never really done anything like this before I wanted to see if any one notices any problems with my design or can offer any improvements. I'm also planning to add an Audison Bit1 and a Car PC later on, but I'm not really sure if there is room for them here. If anyone sees how I might be able to fit them in, please let me know. Thanks!

These are the basic supports for the amp floor. These will be velcroed to the car so I can remove the amp setup for any reason. I'm planning to make the lower support bigger (~5in). I don't think I can do much with the upper support as the floor is uneven on the left, and is slanted on the right. My car doesn't have a spare tire, so the cut out is for a styrofoam piece that holds a fancy air compressor. 










This is the floor to hold the amplifiers. This will be secured to the supports.










This is where I plan to place the amplifiers. They will be on small stands so that the wires can run underneath them and through the amp rack floor.










I plan to build supports on each side like this to support the false floor. I'm going to try and add one to the rear too, but the curved trunk floor might make it tough. I plan to carpet the amp floor and the side supports. I also might extend the sides out by a 1/2in to give the lower amp some more room. Any ideas for fans? I was thinking two at the top and two at the bottom, but again the curved trunk floor might pose some problems. Could I place the fans on the left and the right? The trunk has a vent on the far right as that's where the battery is.










I also saw this example of a false floor. I didn't know if there was any advantage to having the amp floor extend to the available space. I would still have to add supports on the left and right.


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## braves6117 (Feb 13, 2008)

Keep in mind your power runs and signal paths to avoid noise in the system before finalizing amp/processor placement


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## GlasSman (Nov 14, 2006)

No spares in those M3's huh?

Learn something new every day.


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## dummptyhummpty (Feb 4, 2006)

braves6117 said:


> Keep in mind your power runs and signal paths to avoid noise in the system before finalizing amp/processor placement


Will do, Thanks.



GlasSman said:


> No spares in those M3's huh?
> 
> Learn something new every day.


Nope, The exhaust is where the spare would be. The normal 3-series only has the exhaust on the left, while the M3 has it centered at the rear of the car.


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## pagustin (Mar 1, 2009)

The older M3's had spares but most people removed them for the 37lbs of weight savings. 


If you wanted to make the curved edge you could either cut out several pieces That match the curve and are 1/2 or 3/4 of an inch wide and glue them together to match the height of your rack or you could try the "kerfing" technique. For more explanation on that goolge kerfing. I've always wanted to try the kerfing thing myself.  

P


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## chad (Jun 30, 2005)

pagustin said:


> The older M3's had spares but most people removed them for the 37lbs of weight savings.


or they could simply leave 4.2725 gallons of gas out at the next fill-up. That's 37 Lbs, which indeed is one heavy-ass spare, they fill it with water?


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## rcurley55 (Jul 6, 2005)

I think you are going to have to raise the factory floor a touch with those amplifiers (iirc DLS amps are over 2" tall). With that being the case, there's a hell of a lot sturdier ways to build up a false floor in a 3 series, and you can make them light and removable with only a few screws.

Something like this:









That floor is about 2" taller than stock - which is nice because it allows you to remove the factory plastic panels on both sides of the trunk, so now you have a nice flat floor. It also allows a ton more space for wiring.

Just my $0.02


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## dummptyhummpty (Feb 4, 2006)

rcurley55,

I actually tried to model my design off of yours. I've seen your various threads on here and on e46fanatics.com. I'm aware that I'll have to raise the floor and I've tried to factor that in. 



rcurley55 said:


> With that being the case, there's a hell of a lot sturdier ways to build up a false floor in a 3 series, and you can make them light and removable with only a few screws.


What would you do differently to achieve this (light, sturdy and removable)? I've tried to see how you have built yours, but the pictures I've seen (there are a few on your photobucket) aren't that revealing. Since you have much experience with the M3, any advice that you can give me would be great!


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## pagustin (Mar 1, 2009)

Chad the old M-Contour rims and then the Pole-position tire on there was a heavy sucker. Replaced my M-rims with Fikse FM-5 which combined withe the Yokohama tires I saved quite a bit of weight. I left out the spare so I could fill it up with audio equipment.

So what are the measurements of the amps etc?

P


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## jrhavoc (Dec 17, 2007)

I am actually doing the same in my car - I'll get pictures of it when I get home tonight. I used 1/4" MDF in the bottom and glassed around it where the sides and curve are - sits right down in that whole section and kind of "snaps" in place. My amps are almost the same height so I will only have to raise the floor about 1/2", maybe 3/4" from where the factory floor is.


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## rcurley55 (Jul 6, 2005)

dummptyhummpty said:


> rcurley55,
> 
> I actually tried to model my design off of yours. I've seen your various threads on here and on e46fanatics.com. I'm aware that I'll have to raise the floor and I've tried to factor that in.
> 
> ...


We're making progress - baby steps though - pic - E46Fanatics

That has some pics of the build - essentially, use the frame rails as the base and attach a "box" for lack of a better term to hold the amps. Just mock something up with 1/2" mdf for the sides, 1/4" mdf for the bottom (it's plenty sturdy and you can add a brace to the bottom side if you like. 

That gives you the most clearance. The main issue is that the ribbed section closest to the bumper reduces overall depth of the spare tire well - assuming you want your amp rack to be flat and level.

The frame rails are your best reference for "square" in there, so build everything off of them. The only things to be aware of are the two shocks (one in each frame rail) that are connected to the bumper. If you look carefully through the holes in the framerail, you can see them. 

Here are more of my musings over the years about my installs in that car:
E46Fanatics


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## jrhavoc (Dec 17, 2007)

rcurley55 said:


>


What did you use for that trim ring where the cover sits in above the amps? That is real clean looking. I haven't built the top section for the floor yet as I haven't figured out exactly how to make it look nice but that turned out excellent.


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## rcurley55 (Jul 6, 2005)

jrhavoc said:


> What did you use for that trim ring where the cover sits in above the amps? That is real clean looking. I haven't built the top section for the floor yet as I haven't figured out exactly how to make it look nice but that turned out excellent.


It's 1/2" MDF with a 1/4" round-over. Sanded, filled where necessary, and rattle-can painted.

Pretty simple, I just made a recess in the amp rack so the trim ring sat flush with the top of the amp rack. Then the false floor (1/4" mdf) laid right on top - if you cut the false floor correctly (this was done in 5 pieces - the center section, two "wings" near the front of the trunk, and two additional wings near the rear) and carpet it as one piece, you need no additional fasteners. It just lays on top of the amp rack. I added a few braces near the front of the trunk, where there was no amp rack to support the floor so it was nice and solid.

you can see the recess here if you look carefully:









I never understand why people continue to use such heavy stock for false floors (I have looked at build logs where people are using 3/4" material for a floor).

Thanks for the compliment. The E46 trunk is a piece of cake to work in - the rest of the car is another story...


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## CAPO (Apr 12, 2008)

looks good bro


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## Lanson (Jan 9, 2007)

with false floors I usually recommend using Birch plywood, too. It is REALLY light compared with MDF and very stiff. It doesn't cut as well (MDF is the ultimate to cut and shape, as we all know), but it makes a fine starting layer and weighs a lot less.


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## dummptyhummpty (Feb 4, 2006)

jrhavoc said:


> I am actually doing the same in my car - I'll get pictures of it when I get home tonight. I used 1/4" MDF in the bottom and glassed around it where the sides and curve are - sits right down in that whole section and kind of "snaps" in place. My amps are almost the same height so I will only have to raise the floor about 1/2", maybe 3/4" from where the factory floor is.


That would be great if you could post up some pictures. Thanks!



rcurley55 said:


> We're making progress - baby steps though - pic - E46Fanatics
> 
> That has some pics of the build - essentially, use the frame rails as the base and attach a "box" for lack of a better term to hold the amps. Just mock something up with 1/2" mdf for the sides, 1/4" mdf for the bottom (it's plenty sturdy and you can add a brace to the bottom side if you like.
> 
> ...


Yeah, i've seen those pictures. You don't happen to have any more do you? I'm interested in the slanted piece at the rear of the box. It also looks like you built a square and then secured a piece inside of the square to hold the amps, correct?

Do you think I could secure mine to the frame rails with velcro instead of screws like you did?

Your link doesn't work. I've seen many of your posts on E46Fanatics before, so i'm assuming that's what it was a link to.



rcurley55 said:


> Pretty simple, I just made a recess in the amp rack so the trim ring sat flush with the top of the amp rack. Then the false floor (1/4" mdf) laid right on top - if you cut the false floor correctly (this was done in 5 pieces - the center section, two "wings" near the front of the trunk, and two additional wings near the rear) and carpet it as one piece, you need no additional fasteners. It just lays on top of the amp rack. I added a few braces near the front of the trunk, where there was no amp rack to support the floor so it was nice and solid.


Do you have any pictures of your false floor? I understand what you did, i'd just like to see some close ups of the underside of the winged sections.



fourthmeal said:


> with false floors I usually recommend using Birch plywood, too. It is REALLY light compared with MDF and very stiff. It doesn't cut as well (MDF is the ultimate to cut and shape, as we all know), but it makes a fine starting layer and weighs a lot less.


Thanks, i'll keep that in mind. BTW, i'm using 1/4in and 1/2in MDF incase anyone was wondering.


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## dummptyhummpty (Feb 4, 2006)

pagustin said:


> So what are the measurements of the amps etc?


(W X D X H)
The A4 is: 18.30 x 9.45 x 2.87 inches
The A6 is: 16.15 x 9.45 x 2.87 inches


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## ErinH (Feb 14, 2007)

rcurley55 said:


> I never understand why people continue to use such heavy stock for false floors (I have looked at build logs where people are using 3/4" material for a floor).


Truth. Beyond the weight, it just takes up more space. You typically have to put spacers under the top layer anyway. Those spacers do a good enough job of keeping the top layer sturdy. I’ve never used anything but ¼” (anything) and haven’t had any issues. 

Thanks for posting your pics.


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## jrhavoc (Dec 17, 2007)

This is what I have









I'm not completely done yet but its close. I used a piece of 1/4" mdf cut out to lay down in the bottom between the frame rails. I put fiberglass mat down all around the edges of it on the sides and where the curve is, dropped the mdf in place and then added resin. Once it set up I popped it out and added another layer of glass and resin. It fits nice and snug and the mdf is directly on the floor of the trunk. 

These amps are about 2 5/8" tall so close to what you have. When I do the false floor I will have to add between 1/2 to 3/4" along the rails and that will be it - that will allow me to run the wires out underneath the floor and maintain minimum height possible. I don't have the side panels in yet - have to run the speaker wire before I can do that and finish routing the wiring, then it will be build the false floor itself. I was going to use birch but home depot only had it in the pre-warped variety so I bought 1/4" mdf instead and added a couple of supports towards the middle just in case - I use my trunk so I don't want it collapsing. 

In the bottom layer of mdf I used 10-32 nutserts and then used cap screws threaded down into them to hold the amps, eqs, and xover down. The eqs and xover are actually on a raised pedestal so I can run some of the wiring underneath and bring them up somewhat level with the top of the amps. 

I used the well underneath to run all my power wires - it comes in on the right side from the main fuse right off the battery, drops in and runs over to a distribution block mounted underneath where the xover is. If you pull the xover you can access the fuses in the distribution block and all the set screws for the power cables. From there the power goes to each amp - I turned the amps so all of the power cables were on that end so I didn't have to worry about lifting the bottom to run the wiring underneath. The RCA interconnects go underneath the amps for each channel and also underneath the pedestals.

Anyway - that is about where it is at for the moment.


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## VP Electricity (Apr 11, 2009)

Nice amps.


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## dummptyhummpty (Feb 4, 2006)

jrhavoc,

That's pretty cool. Thanks for sharing that.

rcurley55,

Is your box resting on the ridged part closer to the opening of the trunk? Also do you have any dimensions on any part of that box?


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## rcurley55 (Jul 6, 2005)

dummptyhummpty said:


> Yeah, i've seen those pictures. You don't happen to have any more do you? I'm interested in the slanted piece at the rear of the box. It also looks like you built a square and then secured a piece inside of the square to hold the amps, correct?


That's the bulk of them. The slanted part is there to add more depth to the amp rack so it would look ok visually. Past that, it serves no purpose. I needed more room so I could fit the trim ring in and have the spacing be perfect all the way around.

At that point, I was probably recycling installs and used some portions from an old install to make that one happen.



> Do you think I could secure mine to the frame rails with velcro instead of screws like you did?


I am of the opinion that nothing weighing 25 lbs and costing $1500 should be attached to a vehicle with velcro. I used 4 machine screws that took all of a minute to remove. If you are worried about permanent modification, then you really don't want to see my doors. The biggest pain about removing that stuff is the wiring, not the rack! The wiring is the biggest challenge.



> Your link doesn't work. I've seen many of your posts on E46Fanatics before, so i'm assuming that's what it was a link to.


Sorry about that, it's a link to all of my threads on e46



> Do you have any pictures of your false floor? I understand what you did, i'd just like to see some close ups of the underside of the winged sections.


None of the underside. The only wings that folded were the larger ones. I added supports to the amp rack so that they rested on it on the long side, and then put in additional supports so that they sat flat when resting on the car - like stilts.

Here's another photo from further back:









As you can see, I built it so that it was level with the rails closer to the rear seat - so the floor still appeared to be pretty flat - total space lost was about 2"

Of course, there was a grille that would fit into the opening to protect the amplifiers.




bikinpunk said:


> Truth. Beyond the weight, it just takes up more space. You typically have to put spacers under the top layer anyway. Those spacers do a good enough job of keeping the top layer sturdy. I’ve never used anything but ¼” (anything) and haven’t had any issues.
> 
> Thanks for posting your pics.


No prob.



dummptyhummpty said:


> rcurley55,
> 
> Is your box resting on the ridged part closer to the opening of the trunk? Also do you have any dimensions on any part of that box?


No there's some clearance there. This install is very old, so I don't have the part any longer. Just take a straight edge and lay it across the frame rails - and I had about 1/4" between the bottom of the car and the amp rack. IIRC, there's 28" between frame rails? I dunno.


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## jrhavoc (Dec 17, 2007)

VP Electricity said:


> Nice amps.


Thanks - while not top of the line they do work very well for what they are.



dummptyhummpty said:


> jrhavoc,
> 
> That's pretty cool. Thanks for sharing that.


Not a problem and thank you. Once the floor goes in it will surround that whole area and look a bit more "finished" - some of the next weekend's duties hopefully. If it helps in the idea department that is what is important. 


rcurley55,

What did you have for sub duties with that setup? Depending on how the false floor was done a person might not notice at all there is a system in the car. Mine is obvious once you open the trunk and see the sub sitting there and I'm not sure I really like that. I was thinking along the lines of mounting two 10" Arcs or IDQs one on either side behind the rear side panels, or put a 10" or 12" in the passenger footwell like I am doing with my E30. Either one of those setups and I can hide them.


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## rcurley55 (Jul 6, 2005)

dummptyhummpty said:


> rcurley55,
> 
> What did you have for sub duties with that setup? Depending on how the false floor was done a person might not notice at all there is a system in the car. Mine is obvious once you open the trunk and see the sub sitting there and I'm not sure I really like that. I was thinking along the lines of mounting two 10" Arcs or IDQs one on either side behind the rear side panels, or put a 10" or 12" in the passenger footwell like I am doing with my E30. Either one of those setups and I can hide them.


I have 4 8IB4's from JL Audio on the rear shelf. The current amp rack fits entirely behind the false floor.

http://www.diymobileaudio.com/forum/diyma-build-logs/13833-project-m3-underway-8.html#post164470

That's about what it looks like - the wiring in there has since been cleaned up SIGNIFICANTLY.

You can't see the subs unless you look for them - I have full use of the trunk.


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## dummptyhummpty (Feb 4, 2006)

rcurley55,

Thanks again for all your help. I'm going to give this another try this weekend. Keep checking back for updates.

BTW, I'm planning to do what you did subwise, but with a 12in. I talked to local shop and he said he would use double 3/4in MDF for the baffle and would need a bunch of sound deadening. I notice you have a small baffle and what looks like no sound deadening. Is this because you're only using 8in subs?

jrhavoc,

Thanks again for your picture. Feel free to post any updates here. I think i'm going to give rcurley55's amp rack a try just because of the size of my amps. I also suck at fiberglass.


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## rcurley55 (Jul 6, 2005)

dummptyhummpty said:


> rcurley55,
> 
> Thanks again for all your help. I'm going to give this another try this weekend. Keep checking back for updates.
> 
> BTW, I'm planning to do what you did subwise, but with a 12in. I talked to local shop and he said he would use double 3/4in MDF for the baffle and would need a bunch of sound deadening. I notice you have a small baffle and what looks like no sound deadening. Is this because you're only using 8in subs?


I responded in the other thread - you will have to double stack the baffle I'm sure to get enough room to make it happen. I will be a little awkward, but should work.

The baffle is 3/4" MDF (the outside ones are one single piece, the center one is a stack of 1/2" and 1/4"). The sound deadening is on top of the shelf (the inside of the car), and because I put a gasket between the car and the baffle, it doesn't leak.

Pull them down and it looks like a factory rear shelf would


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## dummptyhummpty (Feb 4, 2006)

rcurley55 said:


> I responded in the other thread - you will have to double stack the baffle I'm sure to get enough room to make it happen. I will be a little awkward, but should work.
> 
> The baffle is 3/4" MDF (the outside ones are one single piece, the center one is a stack of 1/2" and 1/4"). The sound deadening is on top of the shelf (the inside of the car), and because I put a gasket between the car and the baffle, it doesn't leak.
> 
> Pull them down and it looks like a factory rear shelf would


Thanks, i'll respond back there.


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## mtxflorida (Mar 27, 2009)

i just finished my false floor, more like a false door that is a 2' diameter circle to get into the rear well just like your m3 has. only 1/2" plywood but braced with 1" by 1"s like a motherfucker


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## dummptyhummpty (Feb 4, 2006)

For any one that is interested, I've done some more work and decided to start a build log: here​


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## jrhavoc (Dec 17, 2007)

Finally got around to finishing the false floor on mine:









Now just throw the M trunk carpet over it and be done. Other than the sub there it doesn't seem to obvious. Latest is having the car almost completely gutted and applying some deadener to the interior. Waiting on parts for the sunroof and then I can put it back together. Now I have to turn attention to the doors and get my midbass drivers installed -can't decide if I am just going to do the 6.5" or attempt the 8" drivers... I'll keep an eye on the other thread - be interesting to see how yours turns out.


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