[quote name='Based']the amp pulls 80a so...
75a alt. around 40% of that is going towards your normal car stuff, so we are left with 60% of 75. 0.6 times 75 is 45a. 80a minus 45a is 35a. After 45a, it's up to your battery to pick up the extra 35a. If your battery is stock then it is probably pulling between 35ah to 60ah. I think if you are not going to go any higher in wattage (like get a bigger setup), then just get a little bit bigger of an alternator such as 100 - 150a and that'll solve the problem and you won't have to have a battery taking up space in your trunk or wherever you decide to put it. If you do think you might go bigger in terms of bass then I'd get something like a 250 - 270a alternator just to prepare for future builds.
But I'm a noob so...[/QUOTE]
This is assuming that the amp is playing a full power sine wave indefinitely... Music is dynamic. A good battery up front and
upgraded battery/chassis grounds is more than sufficient to support a zx750. I agree with @DDtC ; on pretty much all he's said. Clipping, poor connections, or both are the most likely culprits here.
An upgraded alt is ALWAYS a good thing to have in this hobby. But not having one is not the real problem here. Fix the issues... then see if you still want/need one.