What's Inside Silent-Thunder Exhaust?

[ApachePete]

Specifically, is the exhaust from both pipes in an engine dumped into a common chamber?

I ask because the transom on the port side, around both exhaust outlets, is suddenly black with soot. The motor run and sounds just fine. HP500EFI's

I was wondering if it could be stuck injector, dumping too much fuel in one cylinder. But for that to be the problem, the exhaust from both cylinder bank would have to intermix.

Any ideas?

Thanks!

[ApachePete]

You certainly are a very knowledgeable guy!

Thanks for the info.

I wonder if the cross-over is big enough to allow soot to build-up equally around both exits pipes, if only one bank of cylinders had a problem.

Perhaps more likely the whole system is running rich?

[ApachePete]

Water temp is normal (150), BUT last weekend it was up to 200 briefly after I sucked-up some sand. I replaced the impeller, and temp and oil pressures are normal.

Would an overheat cause on over rich condition?

[Bill272]

Here's what mine looks like from a 95 336.

[Formula Outlaw]

On my 89 311 SR-!, a bolt on model, it is nothing like that. Mine is just one big box, with "partitions" glassed in place in front of the rectangular exterior exhaust outlets and in stock condition, small circular holes at the bottom of the box, which are under water when the boat is not on plane. I cut those little circles into big honkin' rectangular holes, and when I look up in there I can see all four very "thru hull" short exhaust tips. I also cut out the partitions. I ended up gaining 300 rpms on the top end by doing this. Sounded better too, not obnoxiously loud, just throatier and more powerful.

[jaybird]

Those little circles that are on the bottom of the "1st Gen" Silent Thunder platform are for inserting drain / baitwell style plugs into. You pull them out to drain after usage or winterization. From what I have been told, keeping the plugs inserted is the way Formula designed the platform to run with water in it to help keep it cool so the platform doesn't overheat and start to deteriorate.

I run with the plugs in, as did the previous owner. I just took the platform off to fix an exhaust leak, and the insides of the platform were in surprisingly good shape for it's age.

[Formula Outlaw]

Jaybird, I didn't know that for quite awhile after I bought Outlaw and did the exhaust mods. For a few times afterwards, after running at higher speeds for extended periods of time, I would physically feel the box to see if it was hot, and it was warm, but not even real warm, much less hot. I would suspect cutting out the partitions helps that heat issue as I now have a lot more water blasting out of the rectangular holes than I ever did before, and if the water is blasting out more it would make reasonable sense that the exhaust gases are also. I constantly check the "raw" edges where I cut to check for deteoriation but so far none whatsoever.

[WAGS382]

Apachepete
I just took the silent thunder off my 1998 382 and it looks very similar to Bill272's, but it also has the balance tubes that Troutly mentioned. I put a set of HPI silencers on, I don't like the sound of the silent thunder.

[ApachePete]

How does the "loudness" compare?

[Bill272]

I took mine off because I was getting an exhaust leak around the edges of it and it rattled. When I looked at it, there was a couple of cracks in the chambers and the one edge was split (where the white kind of moon-sliver spot at the bottom of the pic is.) Where the white spot is also rubbed the gel off the boat under the swim platform there on the side facing the center.

I took it off before the last run of the season and thought the boat was fairly loud before (hp500's). Without the silent thunder, it's considerably louder. I didn't think it would make that much difference since the exhaust exits under the swim platform, but it is a very noticable difference. I like it personally, but I'll fix the cracks this summer and keep it in case they start writing noise tickets around here.

Where do they put the balance tubes on the newer ones??