Formula "Silent Thunder" modification???
 

Hey everybody, bran new to this site, been following it for a while and figured I'd give it a shot. I have a question about the Silent Thunder system on my 1989 Formula 242ls... It is the 454/Bravo 1 set up, and that Silent Thunder is WAY to quiet for me, but everybody's solution seems to be to remove the swim platform and just do thru-hull... I really want to keep my swim platform but also want that thru-hull sound, so I think what I am going to do is get a nice set of Trumpet style tips, and mount them on the underside of the swim platform, and connect them to the exhaust outlets that come through the transom with some exhaust tubing. I think it will sound a lot better at idle, but also won't be too loud inside the boat under full throttle cause the sound will be coming out underneath the platform. I have no doubts that I will be able to make it look really good, I've done more fabricating in my life time then I care to admit, but my question is: What size is the exhaust outlet that comes through the transom? I'm assuming 3 1/2 or 4"?? I would like to know before I start taking everything apart cause I'd like to have all the parts in hand so I can knock it all out at once, so obviously I need to know the size so I can order the correct tips. I appreciate anyone's input who would know for sure the size??? Thanks in advance

Mine is 4" through hull, I think that is standard for most thu hull systems. You could also remove the swim deck and put on an aftermarket deck on and maybe utilize the same holes with just some new tips I'm not familiar with the trumpet style tips so ill have to check that out to fully understand your idea.

Dean

The stock tips are 4". I just finished modding mine.

http://www.youtube.com/watch?feature=player_embedded&v=9fAoxA07PJo http://i2.photobucket.com/albums/y48...386E5ED7D8.jpg

I used these tips.
http://www.hardin-marine.com/p-12590...haust-tip.aspx

Gm I did this same thing a few years ago to my 242 I ran the exhaust thru the platform with ss tubing and hooked it up to 4`` round flush tips with internal flapper, if you go to the Formula section I`ll try to find it I have some pics.

mark

I bet the flush tips look cool! Does the water hush your exhaust for a few seconds when you stop?

If you are going straight out the back like that you should invest in rubber flaps for the exhaust, With the sides and top filled in by the platform, you can stuff so much water up in there while backing that it could fill the engine through the exhaust. That is one of the things the silent thunder prevents.

Wow, thank you everybody!! Those pics/videos are EXACTLY what I had in mind, that thing looks and sounds great! I'm gonna get tips with internal flappers in them just cause I know how close to the water line that is. I was wanting to buy the flush mounted oval tips that they sell as "side exhaust" for boats, and mount them up and down for the flush look, but damn those things are pricey! I'm glad to see that it worked out good on your Formula (fischan), cause I figured I'd be going into this blind since it seems like everyone just throws the swim platform away and does thru-hull the easy way... lol I can't wait to get it started, now I just gotta start makin this turd faster, cause if I get passed by one more damn Baja I'm gonna scream! It's bone stock now with a SS 22P 4-blade, and tops out at 51 (lame) with 4 people and 1/2 tank. I'll start with the exhaust, and then throw an intake and carb on it to hold me over till I can actually build/stroke it. What type of props have you guys had the best luck with?

Quick question Fischan, how were you able to make the tips come straight out when the mounting surface you bolt them to was angled? Did you just grind the mounting flange ob-long so that way it would have room to be cocked at that angle???

I pulled the stock tips, which are really chrome plated brass...not stainless like I read somewhere here. Reinstall the platform without tips. From the inside of the boat, stick rolled up posterboard through the holes till it hits the inside of the ST platform. Then shoot some contrasting color spray paint down the rolled up posterboard transferring your hole to the inside of the platform.

fischan what did you cut the holes with and how did you fill the gap around the tips and hole? where do i get new gaskets for silent thunder platform?

#1 - making it louder won't necessarily stop the Bajas from passing you. Louder does not always equal faster. Nothing is more offensive to me than a slow loud boat. If you make the noise, you better back it up with performance.

#2 - you have baffles in that Silent Thunder platform. It holds water in there so the exhaust has to burble thru it. Cut out the baffles, and half your battle is won. Also holesawing holes directly under the exhaust path about 3" off of the transom will dump the water and give you a freer flowing and louder exhaust. Most people use 2" diameter holes, but you can use whatever size or multiple holes. This method will let you start with a little hole and add more until you get what you're after - not something that you may regret later.

#3 - the rectangular outlets with rubber flappers is fine. No need to replace them with round unless you are just dead set on it.

#4 - yes, I've seen additional rectangular outlets used on the underside instead of open holes. Works pretty much the same as open holes.

MC

That is it. Exactly what i want to do.
Fishan
looks like you started with std platform, what was lurking inside platform?
Any mods to platform, stuff inside to be removed, modified, etc?
Did yours have the o-ring gaskets between platform and transom originally?
How did you handle the seal on the outside of platform?
How far out did the pipes extend beyond the platform?
How did you get the angle correct with the posterboard and get both of them the same?
Gmgearhead454,
did you get yours done?
Any pics?
What did you use?

Yes I finally finished it, I ended up removing it completely, filed the holes, painted the transom, and built a tubular aluminum one. Hard as hell cause of the angled transom, but turned out beautiful. I'm trying to post pics but I can NEVER get pics to post on this site for some reason....

So you completely ditched the formula platform?

Yup. I swear it makes it look 10 years newer. I'll get on my pc later and try to get some pics on here

To post pics easier:

Click on Forum Actions, then General Settings and turn off the Enhanced Image Uploader at the bottom of that page.

Thanks Griff, never saw that before. Still won't upload tho... I've tried from a PC and from my android... >:(

Are you seeing the "upload" button???? It is hidden way on the lower right side and isn't visible unless you scroll over or enlarge the window.

It was a silent thunder platform but I glassed in the rectangular holes. The seal on the outside is 3m 4200 uv resistant. At the top the tips measured something lik 1.5" away from the fiberglass, the bottom was like 4" if I recall correctly, it's been a long time since I thought about it. The angle was more eyeballed than anything, 15 years as a pipefitter/welder. Sold it August 2014.

Fishan, that answers my last 2 questions, hope to cut my holes this weekend.
Thank you for the help.

Hey! I just made an account here so I can contact you. Your exhaust work came out awesome on your formula, did you remove the swim platform to do it?

Hello I'm new to the site I have a 1990 formula 357 sr1 I'm looking to customize my silent thunder platform it off the boat looking to keep the swim platform and chanel the through the swim platform with the exhust and keep the ariginal rectangular tall and flaps any pics or ideas please share

A few people have completed the modification on here, more recently TomZ was going to install this same setup on his old 242. Move over to the Formula section and post there, you may get more of a response. I was going to do the same thing you were thinking but ended up leaving the ST off the boat and installing an aluminum swim platform.

looking to modify my silent thunder exhaust it is just way to SILENT and no thunder !!!! i under stand that people are gutting the baffles and drilling holes ....are you able to do that with the swim platform on if not how much of a pain is it to remove the platform

What model Formula do you have? The modification can be done without removing the platform. My 292 has all the baffles removed and the rectangle ports enlarged in the rear. The ports were enlarged by removing the existing trim ring/flapper assembly and cut larger rectangles out then installed a metal rectangle trim ring that I cut from a piece of stainless. Really changes the sound of the boat with those minor modifications. Others also drill holes in the bottom of the platform with a hole saw to allow the water to drain faster, this is done with a hole saw. The baffles can be knocked out through the rectangle ports by drilling holes around the perimeter and hitting with a hammer. Let me know if you need any more help or clarification. I can text you pictures when i get home if you DM me your #.

I just did this mod about a month ago, just used a long drill bit to drill holesin the top two corners of the baffle and a 12" blade on sawzawl to cut inbetween. probably cut about 80-90% of the baffle plate off. most tedious part is unbolting the factory exhaust tips and flappers. smaller hands would have gone long way for sure!

Build a snarky engine, you will hear it fine.
My high-ish compression 383 with big-ish cam and long tube risers is so loud i have to quiet it down.
I don't think my platform is very silent. Though it was a lot quieter with the OE 350 Mag.

i did the mod myself last year and found that putting a dab of super glue on the nut, then stickin it to the fiberglass holds it there just enough to get the bolt threads started. obviously don't get glue in the threads. once i did this on the second tip, it took a fraction of the time compared to the first side i struggled with to get it buttoned back up.

but having the baffles cut out is how the boat should have sounded from the factory. i even took the rubber flaps off the tips and that really made the difference... at idle it sounds 100% better, with a big, deep, smooth, rumble, but no/hardly any sound increase under power.