what capacitor to buy?

a cap is a cap...the only differences are cosmetic, and some caps have a digital readout on them (which you can make yourself for cheap at Radio Shack if you REALLY want one...) so buy whatever you feel looks good and fits in to your price range, if you must have one... what makes you so sure a cap is what you need?

I purchased a 2.4 farad power acoustic cap for $100 bucks on the internet. I believe it works just as well as some of the other higher end caps.(It's got a digital readout & everything)!

you should look into a new high output alternator first...for your purpose, the cap will only act as a band-aid...it wont really solve the problem, just compound it in the long run... what a cap does is store power for when your system needs it...and when your cars alternator cant accept the load, the cap discharges its power, thereby keeping the amp fed... BUT what most people will not tell you is that a cap discharges pretty fast in any kind of high power system scenario...so then what? now your car has no more juice to give, your cap is discharged, and your amp still needs that power...so what happens? your alternator is working double time trying to power A) your car, B) your stereo, and now, C) your cap...so what you are actually doing is over taxing your alternator which will lead to a premature death of the alternator... a caps function is better used in an ultra SQ setup that doesnt need it to ever fully discharge, but more to regulate the peaks and drops in voltage... the alternator is the foundation of any good system...and just like a building, if the foundation is poor, it will collapse under stress...this is not the area you want to cheap out on...spend the money, get an alternator and do it right...

Ah the myth of caps solve head light problems. I like it, who came up with this idea? Like Big Purds said replace the alternator with a HO. However if you have a car like mine 180 amps os about the max that i can get do to the location of my alternator so i ha to install multiply batts in the rear works the same and doesnt drain the alternator as much either.

Have to agree with Big Purds but a cap should never be used as a band aid. It will not stop your headlights from dimming every time the bass hits. I would suggest you get a high output alternator instead of a cap. But if you still want a cap this site has some good prices http://store.yahoo.com/mobile-emotions/capicitors.html

I would purchase an alternator like everybody stated above as well as a second battery. You need a pool to store all of the extra power your alternator will be putting out. I had a 180 amp alt. hooked up to 2 kenwood 600 watt amps and the lights dimmed everytime the bass hit. Reason being even a big dog alt. can't keep up directly with the damands of the amp, but it can keep your battery full. I have a stock 105 amp alt. and a optima yellow top battery and I am running a 600 watt soundstream 4 channel and a 1000 watt soundstream subwoofer amp and my voltage barely drops below 13 when I am giving it hell.