Br1dgemann

Just as the title says - what precautions did you take after modifying your silent thunder platform - cutting out baffles or straight piping through the box - to prevent reversion or other accidental water ingestion??? I am asking about the older SR1 (1989-1991 vintage) style platforms in particular found on 272, 292 or 311's.

Anything more than just making sure the flappers are working??

Gentle on the throttle?

Slow speed idle in no wake areas??

How about when launching off a trailer?

Any and all thoughts are welcome.

Br1dgemann

Really? Not one person has anything to offer up?

Mr Maine

Just the internal flappers on mine. Make sure they are intact. When you launch the boat, back it in easy.

Its really no different than any other boat with thru hull exhaust.

Splitdecision271

I have a 292 fastech not the older SR-1 model. I removed my silent thunder box under the platform. Had I left it I wouldn't be all that concerned about reversion but now that I have just the flappers, it's a constant thought when doing things.

Coming off the trailer I always make sure the transom is not submerged and exhaust is free and clear before firing up the engines. I also check to make sure I have good water flow coming out after engines are started. Coming off plane I back off slowly and I always give the throttles a little bump to prevent that wave of water from washing back over the swim platform. Same deal with going back on the trailer. I do power the nose up onto the trailer, but very gently and the motors get shut off immediately so that the platform is not submerged.

38fountainecman

I have removed or altered silent thunder boxes on a 1990 292 SR1, a 1986 357 SR1 Kamma and a 1997 419 Fastec. I just made sure flappers either internal or external were on the exhaust pipes. My 357 had exhaust pipes run through the transom with the rubber seals where the water mixed right at the outlet of the pipe with rubber flappers. Also rubber flappers on the 419 with stock CMI exhaust and stock through transom exhaust fittings, 292 had stock internal flappers on stock through transom exhaust fittings if I remember correctly. Never had any issues with reversion caused by water getting in from the transom of the boat. My understanding is that most reversion issues is due to water mixing with exhaust too close to the combustion chambers. I had signs of reversion in my 292 using stock exhaust on the 454 magnums 1 year after new. I went with stainless marine exhaust and used a long riser section that doesn't mix the water until adjacent to the inside of the transom. I also used stainless marine on my 357 on home built 502's where the water didn't mix with the exhaust until just outside of the transom. 419 had CMI on 525SC's and except for cracking of the header leaking water into the block, didn't have any issues. CMI uses a "cool collar" now to minimize cracking.

Br1dgemann

Good information, Thank you.

A couple of questions: Do you stop short when backing in with the trailer to submerge the drives and some of the hull, but no where near the exhaust, then fire it up? Do you back the boat off the trailer under power? If so, after the engines are running, do you motor off the trailer from that location or back the trailer down a little further before putting the engines in gear and easing off?

Br1dgemann

I am thinking that a long riser section could definitely be beneficial.

As a side bar: what were the indicators of reversion on your 292? I have an older 292 with carbureted 454 mags and are curious if the signs were found only after a problem occurred and you tore into the motor. What are your thoughts on resonators in the exhaust tubes for the reversion problem - Mercruiser recommends them for the 454 MAG MPI and states that to get maximum performance out of the engine, you need thru hull exhaust.

I prompted this discussion because our boats sit so low in the stern, it looks like we are dancing near the edge of having problems, and by modifying or removing the silent thunder platforms, are we actually negating a factory deterrent to the problem for the sake of better sound or a little better performance.

GLENAMY 242SS

iTrader: (1)

I am going with straight tips on my 242 and have same concerns. I plan on good internal flappers and a good set of salsbury flappers for safety, fingers crossed.
Good luck

Br1dgemann

What brand of internal flaps are you thinking of using?

GLENAMY 242SS

iTrader: (1)

I have not made final decision on internals. Research here on OSO with no clear winner. Looking at Stainless Marine, Eddie or Hardin. I will need to special order my tips for what I am doing so trying to get it right the first time.
Any thoughts/opinions? (sorry not trying to hijack thread)