You should have a beefed up alternator already and dual batteries because your motor is high compression it needs more power to turn over. So id say throw some true ofc 0 gauge to your alternator and both batteries and you should be good. And as for the amps if just hide those under the seats no need for an amp rack plus its extra weight. I could see if you wanted a show vehicle.

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Since I honestly don't think anyone has given a comprehensive set of suggestions for you, here's my response. Your amplifier is not putting out its maximum rated power. Without knowing the exact model of your amplifier so I can look it up, it's probably putting out less than 250W with the volume cranked up on bass heavy music. This is because of the "8 ohm" subwoofer you mentioned. If it's a single voice coil subwoofer it might be drawing even less than 250W. Unless you have a tiny alternator this likely is not a situation where your amplifier is killing the battery.


That said, I think it would be wise of you to get your battery tested. It will need to come out of the car, or at least be disconnected completely, and attached to a load tester. If you have a battery store nearby, such as Interstate Batteries, they will test it for free. They will probably also do a visual inspection, if you ask, to check out your connections under the hood. This might be fixed by simply putting on new battery terminals, but since we can't see them or do measurements for you we just don't know. The point is, don't just assume you need to spend $200 on a battery or waste money on a capacitor.


I'm going to also suggest, as you've already been told, to make a new ground location for the amplifier. My first choice when installing an amplifier is to find a spot on the floor pan visible from below the car, drill a hole, scrape the paint until I see shiny metal, use a ring terminal that is crimped and soldered, and attach it with a nut, a lock washer, and a bolt. Then I spray on a bit of rubberized undercoating on the underside to prevent rust.


You also need a good ground connection between the battery and the body, as that primo ground connection you will make is just one step. I would do what I call the Big 2, which is to run a new ground wire between the battery and the engine block and between the battery and the body. If the factory battery ground goes up by the headlight support you might want to relocate it to the frame rail or a strut tower bolt. Those locations offer a more direct path for current flow.

Did you ever take my advice?

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Headlights dim because of the voltage difference between the alternator and battery. Because alternators are regulated by demand and sometimes that response can be slow..lights dim. Misconception that the alternator doesn't have enough output it's often just a case of lazy response to repetitive high current demands (bass). In an average setup..1000 watts or less...a capacitor can help with light dimming situations. Make sure the wiring is up to snuff and connections are good. The headlight bulbs will be fine.