I have a 84 272LS with dual 98 stock merc 250hp, 5.7
with 2 bbls with alphas. Also has silent thunder exhaust.
I am replacing intakes with edlebrock performer, dual plane manifolds, edlebrock performer 600 cfm 4bbl carbs,
largest holley flame arrester I can fit, and run exhaust straight out the transom, still using stock manifolds and risers. Also will use the plugs that have the extended tips, I hear that helps. As well as matching the intakes to the heads as best as possible by trimming the gasket overlap. Any ideas on hp increase as well as top speed increase ? Or anyone with tips? This is my third boat, 2nd Formula, but first one I am trying to beef up.

From everything I've read, upgrading the exhaust is most important for power increase. Everyone says the exhaust is the bottleneck for making power.

Are you in fresh or salt water?

I know that about the exhaust, but I dont think that the amount of power these engines have it will be that much of a problem. Getting rid of he twists and turns of the silent thunder and going with straight out the back I figure will help somewhat. Also boat is run in salt water only.

I read somewhere here that the silent thunder platform does not hinder performance.
I believe some one removed it and found there wasn't a gain in speed, only in sound level.
If yopur talking aout eliminating the thru-prop system, I think you'll see something.

Changing the stock exhaust maifolds to a performance type will help, especially if you'r changing cams and intake.
The engine can't breathe if the exhaust is bottled up.

Even if there ie no power gained I still love the sound. My 206ls sounds like a monster compared to my 272ls.
Not changing cams in these engines yet, so hoping to get by with stock manifolds till next year. 2boats is 2much already according to my wife. Also need to find a trailer for the 272. Anybody selling one?

I modified the "Silent Thunder" on outlaw by: removing the partitions in front of the oval exhaust ports, and enlarging the small circle holes on the bottom of the box to big honkin rectangular holes. I gained 300 rpms on the top end. Outlaw is an 89' 311-SR1, 454 mags.

I totally removed the Silent Thunder and gained nothing.
I'm running 330 hp 454 with IMCO thumper exhaust and Edelbrock RPM AirGap manifolds.
I don't think with the 5.7 you will be needing more flow than I do. So save yourself the grief of removing the Silent Thunder.
Also...if you want to experiment without losing the whole S.T. platform just drill 4 - 4 inch holes in the bottom of the deck and go for a run. If you don't like it you can plug the holes with 4 inch screw-in access covers sold at Boaters World and seal it back up with no harm-no-foul with looks and function.
I just installed toe access panels on my 272 for repairs that are in work.
By installing the access plates you don't have to worry about repairing the internal baffle if you don't like the results.
With the access ports on the bottom the holes are covered whither water while in the marina at idle but will "OPEN UP" the flow when on plane. Works kinda neat in my opinion, if you like the sound of wind open pipes!
This is all my .02 worth. but the access ports are a lot easier to liv with. IMHO

FORMULASRFUN:
Check with CUDA he has one for sale that might work.