Hey guys I was wondering what exactly do you gain from porting and polishing the heads and intake? I have a 454 mag and im wondering if its worth my weekend porting and polishing them. How much horsepower could I really gain and mph, if any? What do you guys think?

If you haven't done it before 9 chances out of ten you'll loose power!

Unless your spinning 7 or 8 thousand rpm's with a blown deal, don't waste your time with polishing.

It's just done for looks and the WOW factor on the bench

If you don't know what you are doing you could go backwards really fast. Bigger is not always better. I would recommend not touching them.

I know how to do it, i was just wondering if I was going to see any difference. Its a stock 454 mag with EMI thunder exhaust manifolds, nothing special. Thats why I was wondering if it was even worth my time to do it...

I have done several sets of heads. You would also want to do the intake. The common mistake is removing too much material. I do a gasket match then blend it back, remove casting flash, short side radius, bowl blending then clean up the chambers. To do it right takes a lot of time, you need a good air compressor, rotory tool, abrasives kit, grinding stones, ect... Its hard to get speed out of a boat, you may see 1 or 2 MPH. To get real power you will have to do the cam, exhaust and a bunch of other parts to make it work well.
I see you have exhaust, you are one step ahead.
Gat a roller cam from RMbuilder that will get you some HP.

if you don't have a flow bench you are just pissing in the wind,unless you have experience porting with the aid of a flow bench

I disagree. Measurable improvements can be made by sticking to the basics such as Bowl blending, guide boss relieving and cleaning up casting flash in virtually every stock cast head.

If your port work necessitates the use of a flow bench (for porting purposes), then your in the wrong forum (do it yourself, boating on a budget)

X2.. Good advice

X3 match, blend, clean, 3 hrs, 6 beers, and knowing you did it yourself!
Don't forget to match exhaust manifolds/ headers, after 6th beer.