augie58

one of my winter projects is removal of the silent thunder boxes on my 1998 353 and conversion to tailpipes and mufflers. i am guessing that some people out there have done this. if you can help me out with shortcuts and avoiding mistakes i would be most appreciative.

thanks
augie

t500hps

It's very simple. The "box is held by 4 bolts and just drops away. You'll need replacement tips and mufflers. (Call TRICK!)

Magicfloat

If you don't mind it being loud,you can put clamp on rubber flappers on the existing short tips. May run afoul of some noise laws tho.

t500hps

Robert, Are you sure that the 1 inch tips would be OK. They seem so short I thought it may cause a problem, but don't know what that may be. The factory tips already have a decent flapper inside them to keep the water out, so I'd rather use them.

Magicfloat

We have used them for years with no problems. We leave the internal flappers in,the rubber ones are just an extra safeguard.

Formula Outlaw

I did that on my 89' 311 last winter. Took off the "box" swapped to EMI Thunder exhaust (aluminum/saved 84 lbs per motor) and Stainless Marine tips with the internal "superflapper". Figure I lost at least 200 lbs. with losing the box.

Here some pix.

augie58

how about some help. my boat is a 98 353 with the silent thunder boxes under the swim platform. i have removed the bolts under the rear lip and the couple thru the transom and the box is not falling out . i have pryied the **** out of it , did formula glue the box to the underside of the swim platform ? your help is appreciated

thanks

t500hps

I have a 98 312 with the same box and removed mine 2 months ago (haven't even run it yet) I remember it stayed in place after I removed the bolts but it did come out fairly easily. I can't remember if you have to pull the portion closest to the transom down first or the end farthest from the transom first. there is a lip at the end of the swim platform that kinda holds the thing in place. Also there are rubber gaskets that seal around 1 inch exhaust pipes that come out of the transom.
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HEY, That is what is holding the thing on still!!!! Pull down around the 4 rectangular exhaust ports. Once that comes down an inch or 2 pull down and back to remove the box from the 4 tips.

I was going to put new tips on the back of the boat but have just put rubber flappers on the existing tips. Magicfloat said it would work and it appears it will be just fine.

Good Luck

augie58

i used a closet pole as a pry bar inserting it in the rectangular rear openings and could not get the boxes to drop. i just have visions of someone on the assembly line putting a big gob of adhesive between the platform and the silent thunder box to "make sure it doesn't rattle" . i am thinking of bringing a sawzall and slicing the box open.
oh the fun of boating.

more suggestings are appreciated.

Bill272

Don't sawzall it. As I recall mine had a bead of caulk at the back edge that I cut thru with a utility knife. Then there's adhesive around the exhaust openings and as was said, the exhaust tips are only about an inch long. But the box fits pretty tight around them. After cutting the caulk at the back end, I did the closet pole/broom handle and it dropped about 2 or 3 inches at the back and that was it. I used a pry bar on one end at the transom and then pulled it straight back to get it off the exhaust tips and it came off.