Modifying existing mufflers: adding crossover

[UWSkier]

Through a fortuitous find online, I have a spare set of mufflers on their way to me for dirt cheap.  I put ghetto downturn exhaust tips on my Response a few years ago to quiet it down, which have been great for outside of the boat, but even with an insulated motor box, the sound inside the boat is fairly intense.  I was driving my buddy's MasterCraft with the exact same engine as the Monsoon (basically) last week and the exhaust tone inside of the boat was a bit more muted.  So what I'm thinking of doing is taking these new mufflers, cutting some holes in them, shoving in some 2.5" fiberglass tube stubs, glassing them in, and running a crossover tube between them like the SilentRider option had on the older Malibus.  So, two questions.

1.  Anyone ever tried tackling this, or had a Centek muffler apart to see the innards?

2. Will this do anything, or do the SilentRiders also have additional baffling or something to smooth out the exhaust pulses?

[Woodski]

Lucky you:-)  Inside the pipes are a couple of baffles, one near each end so your crossover tube will need to avoid that section.  Adding the crossover tube is an easy DIY project, I would do it with a rubber hose connection between them to allow some flex in the system (and easier install / removal) which sounds like your plan.  Will it help, yes to an extent although not as effective as a Silent Rider* for a couple of reasons:  1.  Silent riders are closer to the output from the manifold so they catch the pulses earlier in the exhaust path  2.  Silent riders are a rather large plenum so the exhaust gas has a chamber to de-pulse so to speak.  *Silent Rider being the rather large cylinder that mounts just behind the exhaust manifolds / over the bellhousing).

Do you have any sound insulation on the inside of the doghouse?  That helps, I used 3M-400L insulation  (it was the lightest I could find and did what I was looking for and does a pretty decent job, I am sure there are options that would have better sound suppression qualities and 3M makes a 600 version of same stuff).

[justgary]

I was surprised to notice that the engine noise got a bit quieter when I switched from iron to Marine Torq stainless manifolds.  They hold a lot more water around the header pipes, so they get better damping on the pulses.  @Bozboat also noticed the difference when he rode in my boat.  If your iron manifolds are on the way out, maybe different ones would help.

Disclaimer:  I'm not trying to make a sale here, just letting you know what I noticed.

[Bozboat]

30 minutes ago, justgary said:

I was surprised to notice that the engine noise got a bit quieter when I switched from iron to Marine Torq stainless manifolds.  They hold a lot more water around the header pipes, so they get better damping on the pulses.  @Bozboat also noticed the difference when he rode in my boat.  If your iron manifolds are on the way out, maybe different ones would help.

Disclaimer:  I'm not trying to make a sale here, just letting you know what I noticed.

The Marine Torque are noticeably quieter and cooler (both in Temperature and Swag).

[UWSkier]

2 hours ago, Woodski said:

Lucky you:-)  Inside the pipes are a couple of baffles, one near each end so your crossover tube will need to avoid that section.  Adding the crossover tube is an easy DIY project, I would do it with a rubber hose connection between them to allow some flex in the system (and easier install / removal) which sounds like your plan.  Will it help, yes to an extent although not as effective as a Silent Rider* for a couple of reasons:  1.  Silent riders are closer to the output from the manifold so they catch the pulses earlier in the exhaust path  2.  Silent riders are a rather large plenum so the exhaust gas has a chamber to de-pulse so to speak.  *Silent Rider being the rather large cylinder that mounts just behind the exhaust manifolds / over the bellhousing).

Do you have any sound insulation on the inside of the doghouse?  That helps, I used 3M-400L insulation  (it was the lightest I could find and did what I was looking for and does a pretty decent job, I am sure there are options that would have better sound suppression qualities and 3M makes a 600 version of same stuff).

Yeah, I don't expect it to be like a V drive silent rider or like the older Echelon mufflers, but I know Malibu offered a "quiet" exhaust option (which is confusingly also referred to as "Silent Rider") that included a crossover tube from the factory.  Not sure how much quieter it actually is, but I liked the tone of my bud's MC.  I do have an insulated doghouse.  Previous owner did that so I'm not sure which kit was used.  It's padded foil of some sort.

I would love some blingy manifolds, but I just had mine apart a couple years ago and while there's definitely rust, they're still holding up.

Edited June 11 by UWSkier