No sir... your cars battery has wayyy more power than that theres not even a point to put a capacitor on there
there general rule is around 1000 watts RMS is where you should put a capacitor on it, but with a cap you have to be caredful theres a couple Ground rules for caps
#1 ONLY buy namebrand, most caps just look fancy and honestly do nothing!
#2 You want to look for as low an ESR as you can find...
http://www.rockfordfosgate.com/products/product_details.asp?cat_id=5&series_id=40&family_id=87&item_id=108312&locale=en_US&p_status=
#3 Place it as close to your amplifier input as possible, you want to lose as little power in the wire as possible
PEOPLE WHO TELL YOU JUST TO PUT A CAP ON IT KNOW NOTHING!
Also realize a capacitor is only a storage device... how does it take the strain off the battery when every time it hits, it needs to recharge it takes as much power as it uses but the aspect is its another resovoir in case the batter doesnt have the power to hit it will give it the nessecasry power from its resovior