Formula311-SR1

Any good mods to do with the silent thunder exhaust platform? If so how much better performace? Worth the extra noise?

Thanks

halffast_2003

I read somewhere that you can go in through the square exhaust with a long sawz all and cut half moons in the partition.. not sure what it would do for performance.. I like mine the way it is sounds good at the dock but not annoying wehn running

CayFomula

F-tech,

What kind of HP were you running when you tried it with the Silent Thunder off?

I am running twin 454Mag with Whipples and I am wondering how much difference I would see if I took it off.

Formula Outlaw

I've got an 89' 311-SR1, twin 454 mags. I cut the partitions completely out just inside of the rectangular exhaust tips. At the bottom of the "silent thunder box" you will see small circular holes. I enlarged those to VERY LARGE rectangular holes. With "Outlaw", those holes in the bottom of the box are in the water, even on plane at low speed. They don't clear the water, you can definitely hear it when they do, until about 2800 rpms. The faster I go, the higher the boat comes out of the water, and the louder it gets. I gained 300 rpms on the top end by doing this. It definitely made a difference on my boat. It is still not as loud as a typical "straight thru", but I think it sounds healthier than it did before. It certainly runs healthier.

Rambunctious

I posted cutting doghouse holes with a sawzall.

no performance improvement but it does sound better.
kind of like 2 chamber flowmasters . if you know what i mean, then you know what i mean....

i noticed the "improved " in sound most idling along the seawall in the channel heading to lake michigan

a little louder on plane, but still that sophisticated formula sound.

i may take the platform off this winter and check things out. unless by design, the two center chambers are open to each other? i get an annoying resonance at idle when the engines sync in and out.

always was there, not related to the doghouse holes, other than the fact that i could then see through the square tip and see how the whole thing was constructed and the fact that the center chambers seemd open(connected).

Formula311-SR1

Now that is tempting, can't beat the flowmaster sound.
Too bad they are tough on us for noise on the Chain of Lakes we are on.
Hate to do irreversable mods if it's going to get me tickets without a good performance gain.

Thanks for the info guys!!!

hauling ass-a

my boss had a 353 with twin 500, his best friend had the same boat. They did a trip together and the one with out the box used 27 gallons less of fuel. I took my box off when it was brand new so the wife always heard the boat loud but DO NOT FORGET TO PUT FLAPPERS ON THE EXHUST IF YOU TAKE THE BOX OFF! It only takes 10 minutes to take the box off but i bet you will gain a couple hundred rsss

formuladude312

You can do the modifications thru the rectangular exhaust ports with a long keyhole saw, I did it on my 272 and you can cut out more material then with a sawzall, It took a little more time but it looks cleaner, In the top corners of the opening i drilled 2 holes into the 1/4" fiberglass material inside the platform 1 in each corner to start the blade and saw straight across the top, Then you can come up from the bottom inside the platform there is about a 1" space between the bottom and the fiberglass so you can get the blade underneath on each side and saw to the top and it is off in 1 piece, you will have to break the piece in half and i used a long pair of needle nose pliers in order to pull them back thru the exhaust ports to get them out makes for a larger hole inside the platform and definatly increase the sound, But i did not notice any performance improvements, And its not so loud that you would create problems for others just a nice rumble.