1998 740il

Look into "underseat" woofers. They're really popular in pick up trucks because of the limited space in the cab. Plus youdon't have a huge, ugly box in the trunk and you can't even tell they're there.

I have heard that if you change out, or add any components to a bmw electronically it messes up the whole car? I dont know how true that is, do you know anything about that?

This sounds like a problem with the amplifier or the connection to the sub. Now, depending on whether or not the car has the harmon/kardon sound system would determine whether or not there is already an under-seat sub in which case you can just replace it. If it is not a premium sound system you are either looking at replacing the system amp. or all the connections to the low-range speakers...

I am doing a refit on a E38 740I Sport and removing the radio-cassette- GPS combo which is crap to begin with and using a kit already fitted for the space left, keep in mind no more wood is left. It’s all removed and a large unit is used to fill the slot. Now you have a great platform for a much better audio unit, Speakers, all of them replaced and the rear deck and huge truck space is superb for the additional speakers and a subwoofer with a box attacked with the reproduction cone in the cabin not blasting the truck space rattling the licence plate not to mention the entire car as you drive buy sounding like a real ghetto blaster, I prefer true audio harmonics which you are unable to do with a muffled trunk subwoofer you lose the true lows which is the bass you wanted in the first place. All the amps and amp watt balancers are placed in the trunk mounted on the side the CD changer and disc GPS unit were placed buy the factory and the amp for the sub is on the right side, three amps total, 500 watts 4 ohms on subwoofer is sufficient and sounds better, all the amps are at or greater then 1000 watts rated for 2 ohms, 4 ohms cuts the wattage in half, as 8 ohms would only provide 250 watts but if you want it load it will distort and 4 ohms won’t. As for the roomer of screwing up the electronics buy doing this is false, unless you just cut whatever wires and improperly rewire the new audio unit. The easiest way would have been to pick a year where a large unit was already used omitting any wood trim but the price was too good to pass up on a triple black E38 Sport with relatively low miles and not beat up for a few thousand dollars like a if it was a 200 thousand mile 740IA rag doll. True Sport models were not cheap and clean low mile one’s are still not cheap, as good and even better then any E39 540 or M5 auto. Euro models have a manual as well as a 750I sport manual that is still expensive and hard to find. Anyways I have a manual 2000 which is a 2001 here and wanted to use the US version to spec out the car then let my cousin have the auto manual US version afterwards. My last build was a Euro 500SL brought into the US and I returned it to Europe but smoking hot, average cruising speed 185mph top speed was 220 and scary, it was on the very edge but at 200mph quite fine but loved it at 185mph. Now the suspension was a custom fab race track spec as were the brakes, stock it would have been crumpled metal and I would be not here writing this now. Idiots with smart cars would swing over to the passing lane where there are no speed limits in Germany and stopping a car at 185 mph hard would kill stock components and leave you with no brakes after three hard braking, overheated and useless. I have had several BMWs even a prior E38 750IL which was just too long and even thou the 12 was great power stock, the rest was meant for easy driving and better to be seated in back with a driver hauling you around like some diplomat. I will provide the specs after I have finished, also pictures on the process of removing the Audio unit and replacing it. The pictures are the taken the day I first saw the car on a lot.