Silent Thunder Modification.
 

For all those who have already removed your silent thunder swim platforms.

I was wondering if it would be possible to extend the "through hull exhaust tips" out through the back of the swim platform?

I have a 242 SS and have decided that i would like to retain the swim platform but extend the tips out through the back just above the step platform. Then i could lose the rectangular original exhaust outlets.

Does anyone know if this would be possible?

Re: Silent Thunder Modification.
 

I believe the "new location" would be too high with regards to the height of the exhaust manifolds and thus water would flow backwards.

On my 85 242 I had twin small blocks with "straight thru's" but it had the older style teak platform mounted just below the tips. That mounting position I think is considerably lower than the Silent Thunder Box. The teak platform at anchor or tied to a dock was only a couple inches off the water, while the top of the Silent Thunder Box is much farther off the water.

I don't think it can be done without going to some outrageous riser "spacers" which would ultimately require a hatch cover modification.

Determine where the riser starts to make the curve back towards the transom, it's position heightwise, then determine where that would put the new exhaust tips location remembering you have to have "fall" so that water won't backflow (reversion). Look to see how much angle downward the existing exhaust hose has, see from the inside of the engine compartment where the new holes would be cut, then determine how high the riser would have to be.

Re: Silent Thunder Modification.
 

on my 271, that would not be possible at all, the silent thunder box flattens out then and turns a corner then goes out as the rectangular exhaust port. I took it off completely.

Re: Silent Thunder Modification.
 

This is what Outlaw looks like now without the Silent Thunder Box...

Re: Silent Thunder Modification.
 

Having seen how much better outlaw looks, I plan on doing the same, barring any disasters. I think I might go for the 12 degree tips though.

Re: Silent Thunder Modification.
 

Thats what i had originally intended on doing. It looks great, but the missus doesnt want to lose the platform so im looking for a compromise.

This looks good. . .

Re: Silent Thunder Modification.
 

More fool you for asking permission. :eek:

Re: Silent Thunder Modification.
 

If I can achieve as tidy a job as outlaw I'll be pretty happy.

Re: Silent Thunder Modification.
 

Not an option on older style silent thunders, its all or nothing

Re: Silent Thunder Modification.
 

No, that looks GREAT....:drink:

Re: Silent Thunder Modification.
 

If the "flange" is mounted on an angle from a "pipe" that is straight, it won't work. The flange will mate up to the transom on the bottom but be almost 3/4's of an inch off at the top. The pipe itself would have to be bent. I know, I got sent the "angled" flange tips by mistake the first time and it don't work. The hole is drilled at a 90 degree angle to the transom, in otherwords the hole is drilled at the same angle as my tips are showing because the transom itself is angled. Did that make sense????? :D

Re: Silent Thunder Modification.
 

not so fast men ....I been looking at mine and I think you could have the box redone to resemble the newer style platforms ..prob would not be cheap ....but...hell ...whats cheap these days ?

also thought about removing the rectangular flanges and installing 4" round tips ..plus modifing the baffles to get a more sound (noise) ...

Re: Silent Thunder Modification.
 

I agree not cheap at all. I doubt it would hold a person without the bottom support and would need a lot of work.

Re: Silent Thunder Modification.
 

Yank it off, go with new tips, and put an Extreme Marine, or whatever platform on. It would be a lot easier, a lot cheaper, and lose a lot of "dead weight" over the props.

Re: Silent Thunder Modification.
 

Spoken like a real Trooper. :drink:

Re: Silent Thunder Modification.
 

"Thank ya, Thank Ya Vary Much"....:D

Re: Silent Thunder Modification.
 

Speakin of dead weight .....you open that beast up yet ?

Re: Silent Thunder Modification.
 

On my '89 F311 I bought 4 haws pipe's from West Marine, milled the flange down to about 1/4" high, made 4 oval aluminum backing plates, cut 4 holes under the bottom of the platform in line with the existing exhaust outlets and installed. Quite around the dock and let the blower motors ROAR when on plane.Quick, cheap fix that looks good as the hawse pipes were chrome over bronze.

Re: Silent Thunder Modification.
 

Nope, been working all week. Figured on going out last Sunday to see what she'd do but couldn't get a coupler/adaptor for the trailer lights until Monday.

Maybe Sunday if it warms up. Right now it's getting rather chilly down here, imagine chilly up your way too. :drink:

Re: Silent Thunder Modification.
 

AHA! weighed my new Canfield aluminum heads...37 lbs each
Weighed the old Merlin heads...80lbs each :eek: X4 = 172 lbs savings. Guess I can leave my Silent Thunder on for now. :cool: :D

Re: Silent Thunder Modification.
 

just keep the fat chicks off it!

Re: Silent Thunder Modification.
 

Dont suppose you have any pics of the modification?

Re: Silent Thunder Modification.
 

I had installed a teak swim platform originally and now upgrading to this prototype we made out of Starboard with a 34" projection from transom. It's going to mount just at the top of drive gimbles which places it 1" above the water at rest. That's where teak platfrom was mounted and made it perfect for any use.

Going to install as soon as my knee surgery heals up enough to "git 'er done".

Re: Silent Thunder Modification.
 

Would be interested to know what that unit weights. Thanks.

Re: Silent Thunder Modification.
 

"Chicken"......:D :D

Re: Silent Thunder Modification.
 

Been watching this thread with interest. I have a friend with a 1988 311 last season we built new 468's with Revolution Marine exhaust. We then replaced the black exhaust hose for polished stainless tubing. Looks reeally sweet on the inside. We then looked at the swim platform/Silent Thunder exhaust and decided we wanted better exhaust flow (sound). We talked about removing the original platform and using the aluminum tube platform. They, (wife) wasn't sure about that idea so we looked at the existing Silent Thunder system. First thing was to remove the baffles just inside the rectangle openings. Gotta give Formula credit, even the freaking baffles were solid as a rock. Had to sneak the boat to the fire station and use our extrication equipment, (jaws of life) to cut the baffles. Then we cut large holes in the bottom of the boxes so the exhaust water could drain out the bottom rather than get blown out the rectangle ports. The Silent Thunder swim platform is now an echo chamber that still has a deep throaty sound but deffinately picked up some decibles, especially at higher RPM's. The big plus is it HAD to allow the motors to breathe a lot better. We looked at running tips or stainless tubing out through the rectangle holes also, (as was mentioned above), but was going to be a lot of custom work with little if any performance gain.
I admit I love the looks of y'alls boats with the platforms removed, but if you can't, or don't want to remove the original platform, there are ways to open things up.

Re: Silent Thunder Modification.
 

You've met my wife :o :D :D

I also prefer the look of the platform. Makes it look bigger so my 27 looks like a 29 :rolleyes:

Re: Silent Thunder Modification.
 

I am assuming that on the 242 the exhaust tips would exit around the red dots on the attached picture.

If thats the case, the heavy internals could be removed to lighten the platform, the original rectangular tips could be removed and made good and the new tips could exit at the points shown and be fitted with salisbury flaps to prevent reversion.

What do you think?

Re: Silent Thunder Modification.
 

HAven't had a chance to weigh the Starboard platform yet--I made the mistake of loaning my PU truck to someone so I cna't get it home. Last time I was at the shop it seems like it weighed about same as old teak platfrom that's in the picture also.

I know that's a lousy answer--but at least a comparison for now.

Re: Silent Thunder Modification.
 

You are going to have to find a reference point to determine exactly where the exhaust tips come through the transom. I believe you will find they are much higher than your red dots. On my 311, after I had modified my Silent Thunder Box, much in the same manner as the above thread, you could easily look up inside and see the short tips coming through the transom. They were probably seven inches higher than the rectangular tips. Look at the picture I'm including here and take note where my new tips exist the back of the boat. Notice the relation to the distance from the rubrail. I don't know if it's the same on your boat but what you could do is take a measurement from the inside of the engine compartment from the top of the exhaust hose to "something" then transpose that measurement to the outside and you can then determine approximately where they will exist. Hope that made sense.

Be sure to check the next post.

Re: Silent Thunder Modification.
 

I have no idea if the motors are mounted in the same position, but note that my tips are quite close to the rubrail, and quite a bit higher than the gimbal of the drive.

Note that you have your orange "dots" located basically at the gimball height, which would mean the tips coming through the transom would be at the water line. I think you're going to find that is not the case. I'm thinking they are close to where mine are. Check to be sure. Hope this helps.

Re: Silent Thunder Modification.
 

ER ...is a 29 ....just put it beside a 292 fast tech ....

Re: Silent Thunder Modification.
 

I know , it's almost identical. But it's still called a 272
A few years ago when I still had my t/330s I got beat by a 29 Fountain with a single HP500. Back at the ramp I was parked next to him while tying down and realized my 272 SR1 was actually BIGGER than the 29 Fountain :eek:. Now minus two feet for his swim platform and 2 feet for th beek it's onlt 25 feet as measure in Formula feet. Now subtact 1200lbs for a big block and drive...it ain't no wonder he was able to nose me out............................................... .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. .................................................. ............................................
but no more ;) ....

Re: Silent Thunder Modification.
 

Outlaw is right, I rebuilt my swim platform two years ago on a 242 back then and the exhaust is at the same height as the 311. I have one picture but no way to scan it, sorry. I would still measure several different ways to be sure but thats what it looks I to me. The actual holes are real close to the bottom of your name on the back of your boat about where you stand on the swim platform. Hope this makes sense and that it helps you. Propwash

Re: Silent Thunder Modification.
 

I was making plans to do the same thing with my 272 (twins)
I have removed my silent thunder to repair it. (replace wood at transom mount surface. )

I had already cut out the baffle plates and it sounded better, but was going to extend the exhaust "hose" all the way to the silent thunder tips, fabricating a roudn to square interface bracket for the inside.

I found some corrogated marine exhuast hose that is quite cheap and was going to use it. But talking to my boat'n buddy ( while snowmobiling...Michigan is a great state...anyway.....) he said corrogated creates a lot of back pressure.

So I plan to look for some preformed smooth hose.with the needed offsets. ( straight on the inboard, and about 4" on teh outboards . On my twins the thru hulls exit out the transom clearly higher than the square tips. especially at ride height sitting in the water.

I feel this will add some sound to the exhaust, gain no power, but eliminate the weight of the water inside the silent thunder and the exhaust leaks at the transom.

so does anyone see an issue with doing this to a twin setup?

Ramb

Re: Silent Thunder Modification.
 

Once you get your "round to rectangle" adaptors made up, they make a reasonably flexible smooth wet exhaust hose that should be able to make the bend. I saw it in either the West Marine or Boat US Catalog I think.

I used a smaller diameter of this hose for my exhaust plumbing and it amazed me how easiy it would make a tight bend. Worked great.

Re: Silent Thunder Modification.
 

Well, I completed the project.
sounds good on the driveway. will splash on May 25 ( after the ice thaws here in Michigan :rolleyes: ) actually our first boat club run on Lake michigan that day.

sounds good, similar to other boats with straight exhaust. louder than the silent thunder. We'll see how it sounds at load and rpm soon

engines really need some lumpy cams though :D

See my post for "thru thunder modification" for pics

Ramb

Re: Silent Thunder Modification.
 

i took my silent thunder off my 271, then put stainless marine manifold and risers on, it is barking like a big dog now!

the difference in plane time on the boat is dramatically faster