need power

First, what do you mean when you drop the amp from 2ch's to 1ch? What sub(s) do you have connected to the amp -model #'s please?

Have you done the Big3 Upgrade?

Ditch the cap. It is contributing to your problem.

Well, all right! You fingered it out!

I have four 10 inch mtx blue thunder legends that r 4 ohm each

and i thing the cap is what is keeping me from frying my alternator and im looking at a 140 amp alternator would that stop the problem

The cap is making things worse! It is another piece of equipment that the alternator is struggling to keep charged. Get rid of it and you'll notice a big improvement.

Wire 2 subs to each channel in parallel (both sub +'s to amp +, both -'s to amp -). This will load the amp to 2ohms per channel. Audiobahn states the amp is .5ohms stable per channel (bridgable to 1ohm = .5ohm per channel), but I wouldn't push it.

The 140a alternator will help, but I doubt it'll take care of all your electronics PLUS the cars' electronics. But, it will help.

For your current alternator, 4g welding cable is fine. If you upgrade to the 140amper, you should go ahead and do the Big3 with 2g.

please tell me how the cap is the problem b/c thats where im getting my voltage reading at and the only thing i'm losing power to is the amp the rest of the cars power is fine b/c the lights arnt diming