l have 800 watts RMS Amp at 2 ohms and a 4x139 RMS Amp at 2 ohms.My car has a 105 Amp alternator.l am running all of this on a 1 gauge wire.

your alternator is perfect for just 800 watts but just in case for any reson your lights start to dim which is unlikely with your alternator, you might to look in to an optima battery and the big 3.
hope it helped

That is a decent system, but no you wo not need any extra equipment. Maybe a 1 FARAD capacitor, but nothing more. If it was over 1500w system then maybe a high output alternator would be needed, but not in this case. You will be fine, maybe the lights will dim a little, but not much at all.

lil kran leave the advice to people that know what they r talking about. There is no way on gods green earth that this guy needs a cap for anything. All a cap is going to do is make yet another current draw from the electrical system to charge. THAT IS IT AND NOTHING MORE. It is not going to give u any extra energy what so ever, ur lights will still dim. If u want to upgrade ur electrical system to handle more power then look into doing the big 3 upgrade, a High Output alt, & a deep cycle battery (optima yellow top). Also the 1 ga wire that ur using for u sub amp & speaker amp is overkill, use the 1 ga wire to a distribution block, then run 4 ga wire out to ur amps, especially 0/1 ga wire is recommended for 1500 watts RMS & above, not less, 4 ga wire is recommended for right where ur at. Since u have a 800 watt amp (4 ga wire recommended) & a 139 X 4 rms amp (again 4ga wire recommended).

You're fine with what u have. Cap not needed.

Just be sure to set the gains right.

The purpose of the gain is to match the signal volts RMS coming from the source (CD player, etc.) to the input of the amp to prevent clipping (damage by over powering).

Here is a guide that will help u set the gain correctly http://box.net/shared/uchv4dbk88

You will need a multi-meter (AC voltmeter, $15 from Radio$hack), Microsoft Excel & a way to burn an audio CD from an MP3.

If u do not have Excel, use this link http://box.net/shared/nkkw1dhk4g

See my site for more info http://spkrbox1.spaces.live.com