Silent Thunder Exhaust.....how do I Create less restriction
 

I am upgrading the motor in my 91 formula and I am looking to allow the exhaust to flow more freely. I want to build a 496 stroker motor over the winter and i think i am going to need to do something with the exhaust. any ideas and where i might be able to find somethings for it.

Call Formula and ask for the TAG group. Chances are that they put some reasonably big power in those boats over the years, and that you'll be fine.

I cut the bottoms out of my 1990 292 sr1 silent thunder and also removed the inner baffle. If I remember correclty, Formula glued the baffle in and I either poped it out with a hammer and extension or cut it out. I left the stainless exhaust ports and rubber flappers in place. The other option is to cut the inside wall of the outside exhaust chambers and cut the bottom out of the inside chambers. I actually like the boat much better with the louder exhaust. It was not obnoxious, but had a great "rumble" to it. Did the same thing with my 357 sri and removed the one from my 1997 419 fastec and sold it to a guy in N.Y.

how was it you were able to get to the mufflers in the swim platform?

They're just vertical baffles. Take off the rubber flappers and reach in there with a long-bladed sawsall. Metal blade works well, wood blade is too aggressive for the fiberglass baffles.

If you do a search there are I think two threads that talk about the removal of the baffles. IMO you do not have to do this for more power.

I like third bird's approach. If I remember correctly I may have used a long drill bit, drilled a bunch of holes around the perimeter of the vertical baffle and knocked it out. It wasn't pretty, but no one sees it. I feel you will get a little more power if you increase the hp of the engine. Stock engines won't see a difference, but I beleive higher hp's will.

also you can get the larger rectangle tips that they used on the 575 boats along with cutting the insides and or cutting holes in the bottom

I didn't know they made larger tips!! Learn something everyday.

So, evidently higher power does require a little more relief than the stock setup.

I had a 242 with a 630 hp 502 blower motor in it. I installed two Bomar High-Impact Polycarbonate 4" Screw-In Deck Plates one by each drain hole. You do not have to fool around with the baffles. I also found a pair of old Stainless Steel Formula exhaust outlets, cut off the bottom of one and the top of the other and welded the two together which doubled the size of the exhaust outlets but you could skip this if you add the Bomar deck plates. You have the choice to screw the covers in place for a little quieter ride or leave them off for a great sounding rumble. My friends used to say it sounds like it want's to go fast when it was idling and the police will not bother you. If you email me I can send you a short video.