ok, how far above waterline is top of riser? sposed to be something like 14 inches. I think about 6 inches of riser extension would help a lot. then you also have enough height to cut holes higher. those stern power drives are pretty nice setups. scarce. hard to get parts for-not impossible. but sturdy drives. kinda like Betamax. just cause it didn't sell doesn't mean it is junk.

Riser height is very important, but, tailpipes under water are done alot. Look at some of the Eliminator Eagle's and such...many of those have exhaust under and running some pretty crazy motors. Those would be the exhausts to look into to see how they don't drink water from being under water.

i know on the inboard ski boats the engines are mounted pretty high and the water cant go that far up hill.i dont know if your boat was built with the current exhaust but i agree that the risers need to be raised and maybe the exit holes filled in and raised up.until you can make these modifications i would concider internal and external flappers.

A little tip everyone hanging around and off the back end of that boat causes water reversion as well just sitting there especially when waves slap up against the transom.. many boats with the extended swim platforms where everyone hangs out on in party cove experience water reversion as well no matter what form of exhaust setup they have. You are lowering exhaust waterline / boat waterline. (deeper in the water). It would be wise to put riser extension blocks to raise the height. of the exhaust system.

first buy a brand new set of Salisbury exhaust flappers. when old, the hinge is looser. new ones stay closed better. then there are exhaust tips with internal flappers. I don't know of any add-on internal flappers that could be added in the middle of the hose, but if somebody designed and built one, I betcha it would sell...oh, and BUP, this isn't reversion. reversion is when engine sucks water back in while running. this is intrusion or submersion or glug glug glug.

Dangerzone, can you post a pic of your engine compartment? would give us an idea how much downhill you have in exhaust run. and I thought of an EASY cure. sell it to me!!!

there is next to no pitch on the system... along with less than a 4 inch rise on the system i think the water is easily coming in,,,i cant seem to find a in line type flapper that will fit in the system.. synamic speed marine is going to look at the boat and see what they can come up with... i know the proper fix... but i just dont want to say it out loud..

first buy brand new Salisbury flappers. then look for tips with integral flappers. then look for manifolds you can put riser extensions on or something aftermarket with tall risers. brand new external flappers stay closed. they are cheap and 5 minute install. or sell it to me!!! actually can't afford anything yet, but soon I will be shopping for a 24/7 or 22 Avanti.

Do you have a jet boat type snail system ? With your transom exhaust locatgion being so low, a standard riser located over the manifold would have a bunch of 'fall' angle.

Don't say 'sell the boat' - that is letting the machine beat you. Well, I guess that would mean you beat yourself, but we can blame the machine can't we. LOL.

Its a 454 with a 502 cover on it...last guy that owned it....