Wondering what are the disadvantages or advantages of a dual air intake. Thinking about fabricating one for myself

For what car?

Knowing what kind of vehicle.what engine and year would help greatly

Intake is intake. If space confinement means you need to go with dual, all good. But the fact there are two does nothing vs one. It'* more a matter of not allowing the size of the intake to restrict air and create vacuum. Regardless of how many "channels" you create for the air. Also to consider is, does your mods create a need for more intake.

Pontiac Bonneville. I recently switched from K&N to Spectre for my intake because after hearing some controversy I went to the websites and their CFM is significantly greater. But on their website they have a fabricated Y-pipe for dual filters and was wondering would it make a diff. I know it does on cars like the 350Z and G35 and even the stealths/3000gt'*. But would it help a 3800 engine or harm hp

More flow is better. If you put a vacuum gauge between the filter and MAF, you want as close to zero vacuum there as possible. So two filters will allow better flow, for less vacuum.

Thanks Danthurs! So two IS better than one. . .

And as far as the Spectre intakes go, someone please correct me if I'm wrong

I woudl have to look at them to make a comment. I use a K&N oiled filter, high air flow.

I was using K&N too but at one of the recent auto shows, SEMA I think, they did a side by side comparison and Spectre outperformed it. I saw it on an online thread somewhere. As soon as I saw it I went and grabbed one. They have one that has the highest CFM I've ever seen but I couldnt figure out how to mount it so I took it back and got the one that'* on there now. It'* a bit big but it'* still light and serves its purpose