what do i need to keep voltage up?

An Orion 2500D?  That amp will croak a Nissan Sentra alternator.  It requires a 200-amp fuse or circuit breaker.  You definitely need a HO alt of at least 250 amps and big-3 upgrade to 2-gauge or higher cable as suggested numerous times above to run that large an amplifier.  And no, batteries alone will not help.Support the12volt.com

think of it this way. you run let's say a 75 amp alt and run an amplifier that pulls 120 amps that alt will be working all the time to keep up with the demand. now you decide to put in a 200 amp alt now the alt only has to work almost half as much to keep up. do the math and figure out  which will consume more horse pwr. and if you add a battery to a 75 amp alt you just compound the problem. now the alt has to keep up with your electrical and two batteries.

It is very simple and it has been said to you before....It takes power to make power. We have 2 honda's   we have upgraded both cars with a high output alternator, we have not had any diffrences while driving on the street, nor have any of our #'s dropped at the drag strip. If you order an alternator correctly, like the instance we are in, We have large case Chevy alternators of both of our honda's...But the pully is the exact same as the stock pully on one car, and the same size as the underdrive pully on the other. If you go through a honest shop or dealer for your alternators they will have the same size pully and will be made so you will not lose power. I will say this once,     If you install a 2500D and attempt to run it on the stock alternator intend to replace it soon,   if you run it with additinal batterys, prepare to replace it again.2009 0-1000 Trunk WR 154.0DB 2009 1001+ Trunk WR

2007 USACI World Champion

2007 World Record

2006 USACI Finals 2nd Place

what size alternator should i upgrade to? where can i buy it for a 02 nissan sentra?CoCo

ok i have one more question...i should upgrade my alternator first am i correct?  now after i do that, do i have to swap out a optima battery in the place of my stock battery? i want to do the big 3 first...i know you run a wire from the positive on your alternator to the positive on the battery(can be fused or not fused?), then another wire from the negative on the battery to the chassis, and then from the motor to the chassis, but how do i do the motor to the chassis, does anyone have pics?  should i do this first and see if my lights still dim, i think i have a 100 amp alternator, and my amp i have in there now only has 2 40 amp fuses so its 80 amp...its a ma audio hk897 i wanna upgrade because i was told that amp doesnt really push out 1200 watts more like 400, because its not that good of a name brand...CoCo

yes you can and should upgrade the battery. on the big three you got it right and there should be pics of it on cardomain and full instructions. the big three will fix your dimming problem for know with the amp you have. but once you are about to get the orion install that ireggi alternator or what everone you chose. good luckJUST ONE MORE AMP!!!

hu,alpine cva 1005/dva 5205

sound processor,symmetry(first one).

sub amp,power 1000 the terminator.(1992).

subs,spl comp dual 1 ohms.

punch 150hd on a 10" ev.

alotofhighs

i cant find a good alternator for a 2002 nissan sentra spec v...ive looked everywhere and i cant find it, im not sure if mine is 100 amp stock or 130...im going to try the big 3 first...and see what happensCoCo

i just looked on car domain and couldnt find anything can anyone find me the link to the big 3 and instructions CoCo