i have a stock 454 carb mercruiser and have few questions....
1. what does a drive shower really do and will that help in performance?
2.looking for a good cam kit to add lil speed but mostly for sound any good reccomndations?
3.i have thru hull exhaust and wanna replace stock manifolds with some thunder lol whats a good marine header that sounds good and loud lol for a nice price
4. any other small bolt on mods u can think of would be nice

A drive shower cools the top of the drive. It does nothing for performance.
Lots of good cams out there. Are you carbed of efi???
Look at Revolution Marine exhaust. Good exhaust and bargain priced.
Little bolt on mods will do little or nothing for performance.

Don't do anything until you can afford a decent set of heads and intake. That exhaust needs to go with it. Then you can do all the little stuff.

Sound advice from the guys above.

Start with the exhaust, then go into the motor from there. Just plan ahead on the exhaust that you choose, because it will dictate how big of a cam you can use in the future. I'd look for something with a dry tailpipe, if you don't care about how loud it is.

1) The drive shower will cool your drive as stated, this is a reliability measure for high HP applications or hard working drives. If you intend to boost HP, they are a good addition. IMO? I'd put one on just to be safe.
2) What year / Mk / Gen is your engine and how much work do you want to do to make the cam work? For instance:
-What heads do you have on it now?
-What intake / carb?
-What pistons / compression?
-What exhaust?
We need to know these things in order to recommend something to you that will work.
3) I think the lads have covered exhaust beautifully. Go dry if you can.
4) Upgrade your ancillaries: Oil Cooler and lines. Filter, adaptor pad (for remote filter) oil fittings, fuel fittings, fuel line (from tank to carb), fuel filters, fuel pump. Run AN-12 oil and AN-10 fuel. Also read up on which Oil to use and which filter, it makes the world of difference.

Each engine is different, but there are a lot of key comoponents out there you can find that will help, we just need to know more about your current set up to help out!

Get the exhaust first before you do a cam change. Get long risers to avoid reversion.

yes it is carb not fuel injected
ok what exactly is dry headers ?
motor is completely stock.
im not really looking for much power mainly sound but any power or mph i get will make it even funner at times

sorry for all questions im new at the inboard scene this may sound like a dumb question as well so if i decide on the dry headers where does the water discharge out at

You really don't need dry headers unless you go with a very big cam. Most dry headers have a separate water dump on the transom.

Just get some good aftermarket exhaust with long risers, no silent choice if you want a performance cam. If it is too loud get mufflers. EMI, CMI, Imco, Dana all make good products. Be sure to upgrade your oil cooler. I used RMbuilder for my cam, do a search and you will find good reviews.