I have a big drain on my car as well and still have my stock 2010 Honda fit sport alternator.
I have 4 12's walled off and one 1400 kinetic battery. Regardless of the battery, if I turn my gain up enough my cars interior lighting dims due to the drain from the subs. It been so bad that it shut off my cars power steering. I need a bigger alternator and battery and need help cause I have no idea what I'm doing.

 

I think the problem is momentary. A larger alternator and starter battery should not be needed, unless you're powering extended concerts at Shea Stadium.

I think people typically put a second battery close to their sub-amplifier and/or use capacitors for instantaneous power, with some sort of diode isolation circuit, but this is beyond my Car Stereo 101 knowledge. Google?

There is some chatter about disabling the electrical load sensor to have the alternator always active, but I don't see how this would be sufficient for high momentary loads.

There's always the In Car Electronics forum (I.C.E) too.

poor fit.

 

First I would read this other install log: https://www.fitfreak.net/forums/2nd-...stall-log.html

I think Fit4Spl even had a solution/custom alternator made, but did not run it in the end.

 

I believe without knowing your actual setup that you are seeing a large voltage drop because your amp isnt getting true battery voltage to begin with. less voltage means a huge amperage drain.
EDIT also, if your subs are using small wire for power between them and amp, amp will draw much more power as well.


What size is the power wire?
what size is your ground wire?

Did you do a grounding kit under the hood? Im stock, and I noticed much less light dimming when locks and radiator fan operate

 

I have 0 gauge going from under hood battery to the back of the car where my sub amp is located. I think i have 4 gauge going from the amp to the 4 subs but do not remember.

I have a DDm3 amp 2000x1@12v.