Quieter exhaust?

I have an '89 Saltare which has a 454 and straight pipes, too loud. I'd like to quiet it down. I first looked for SuperTrapps as they were factory on earlier boats but are NLA unless you can find NOS. Given that I see two options:

One is the common fiberglass ski boat mufflers. None I've seen give a decibel reduction. Anything is better than nothing, but installing these would require cutting the floor and glassing in new wood so I'd rather not do that for an unknown change. I also see many threads mentioning these blowing out or cracking causing leaks, not great for anything at or below the water line.

Another is transom mount mufflers, such as Hardin Marine offers (https://www.hardin-marine.com/p-1260...silencers.aspx). Theses claim 8-10 db reduction, or about half as loud. They're also compact and should be an easy install after getting the gas tank out of the way. I'm leaning towards trying these first and if still too loud I'll put the long ski boat mufflers in front of them.

What options do you guys recommend or have tried to quiet down your boats?

I ordered the Hardin Marine transom mount silencers (https://www.cpperformance.com/p-1259...silencers.aspx). I was worried about the flange size and whether it will fit inside the recessed part of the hull. My exhaust tips are 3" and these require a 4" hole, so I'll have to drill out to 4". I was worried about the flange size fitting in the recess around the exhaust tips, but the flange it 6" OD which will fit with a little room to spare.

After ordering I realized my risers have a 3.5" outlet, so it may have been more prudent to order 3.5" inlet transom mufflers and just get the 3.5" in/out ski boat mufflers as well tomaximize noise reduction while minimizing impact on performance. Realistically at marginally more power than the stock 330 HP I don't expect an appreciable difference in power. I've run 450 HP big blocks in cars through dual 2.5" exhaust, so 3" should be fine for a wet exhaust. The factory pyramid manifolds and risers are probably more of a restriction than dual 3" exhaust with mufflers. I'll see how these do and hopefully I don't have to tear up the floor and install the long ski boat mufflers.

Why no FAE type solution?

I have heard mixed reviews about the effect on the wake. I've not ruled out FAE, but it will be a last resort for me. The transom mufflers arrived today, so I should be able to get them installed this weekend.They seem like quality parts and have an internal flapper. I'll add a flapper on the end as well which should dampen noise somewhat from my experience with exhaust being noticeably louder when I had a flapper tear off. There is a .075" gap between the OD at each end of the muffler insert and the ID of the tip though. I may try to flare the inserts to fit more tightly in the tip and use a sealant on them. I'm cautiously optimistic, but suspect I'll be adding ski boat mufflers as well. I doubt that would be inadequate, but if so I'll try FAE at that point.

Refresh my memory here Cadunkle, you primarily wakeboard behind your boat right? Are you talking about the resonating exhaust noise out the back or does it carry into the boat?

Yes, primary wakeboard and kneeboard. It's too loud both in the boat and behind it.

I got the Hardin Marine tips installed today. The factory hole was 3.25", which I enlarged to 4" by using a 3.25" hole saw inside the 4" hole saw to serve as a guide. The existing hoses were the perfect length to get two clamps on each end. The original install has two clamps on the stainless straight pipe and one clamp on the tip. The original tips were plastic and had melted a fair amount. They also came right off with zero effort after loosening the clamp and removing the six screws. My bilge was dry for a couple years after replacing the rudder and resealing the platform brackets, but these must have started leaking.I don't feel so bad however this turns out as apparently it needed to be done anyway. I sealed the new tips with 4200 fast cure on the flange and smeared on the pipe and in the hole in the transom. Screws are #12 x 1" long, I reused the factory screws. The transom is about 1" thick toward the top of the exhaust hole and 1.25" towards the bottom.

It won't be indicative of noise level in use, but I'll fire it up tomorrow in the driveway without the inserts and measure decibels at idle then install the inserts and measure again. If weather and other factors work out I'll take it out Sunday and get my subjective impression of noise reduction as well as measure decibels in the boat at idle and at speed.

And the installed picture...

Decibels as measured with a cheap Risepro $20 meter accurate to +-1.5 dB. I measured idling in my driveway standing 20' behind the boat and a few feet to the right, as well as at head level in the driver seat with pickup pointed to the rear. I measured a 5-6 dB decrease from both measuring positions. A 3 dB change is double or half the energy (or pressure) in the sound, though due to how the human ear hears sound a perceived doubling or half the loudness is closer to 10 dB. Considering this, even 5 dB is a significant reduction for my purposes.

No baffles: 87 / 77
Baffles: 81 / 72
Baffles+flappers: 81 / 72

Subjectively it is noticeably quieter and a lot of the harshness is taken out, but not as quiet as I had hoped for. The internal flappers are quite loud as they flap back and forth though I suspect that won't be noticeable in the water as they'll be under water at idle. I suspect with on the river at higher RPM, an unrestricted water supply, and more water flow they will muffle slightly better than on the hose. Judging from the design of the baffles the amount they will quiet it down is probably highly dependent on the amount of water flowing through them. Adding the external flappers didn't measurably change the loudness but subjectively changed the tone or harshness standing at various points around the boat. I'll leave them on as my experience years ago when one of the flappers tore off is that it was noticeable louder riding behind the boat.

I'll update with a measurement from the drivers seat on the water. I won't have a straight pipe measurement but if there is interest I can pull the baffles at some point and compare. I suspect I'll be installing additional mufflers though, but I'll see how it does on the water first. If I want quieter Ultra Marine makes a ski boat muffler that should fit at 43" long and only 4.25" OD (https://www.myinboardmarine.com/coll...le-um-288-3001). They also make the same muffler with a 3.5" in and 3" out, I don't know that it would make any performance difference with the same internals output size but it might make the connection from the risers easier to have a longer hose and eliminate the reducers. I could always get a 3.5" muffler and relocate the reducers to the rear in case I ever wanted to swap for 3.5" in tips. Approximate measurement from front of straight pipe at the leading edge of the flange to the back of the back seat is 40". That could work out so the output flange of the muffler pipes through the bulkhead by about 2" or enough to fit two clamps for easy future servicing. Either way it's in the ballpark and I can make it fit if need be.

I put a FAE on my 1995 comp that we only use for slalom. I can say it changed the wake, but I can't say it made it worse. At ski speeds it may have made it a little softer. Wakeboard speed looks unaffected.

Thanks for the info on the wake with FAE, that makes me feel less concerned if I end up going that route.

I spent the today on the water. It may be my imagination but I think there's a little less rumble and vibration at idle. This is plausible as the baffle could break up large bubbles into smaller bubbles. Noise at idle is of course not an issue with the exhaust under water.

The first time accelerating there was a very noticeable decrease in exhaust volume. It's still loud, but also more mellow and not as harsh. The admiral immediately commented that it's much quieter. I'd imagine the noise will not carry as far or be as loud on shore or riding behind the boat, though I did not ride today. I don't have a measurement without baffles to compare to, but at 22 MPH I see 84-86 dB in the drivers seat. The same or slightly more up to nearly 3000 RPM. For comparison on the way to the ramp I take the highway. Towing at 65 MPH with windows down I see ~88 dB in my truck, and 91-92 dB from tire noise as cars pass.

Above 3000 RPM it was over 90 dB and getting louder as I accelerated, unacceptable to me. I did not think to do a WOT pull and check noise at max RPM, or if the Hardin Marine tips affected top speed or RPM. I'd imagine not with my wee little PCM 454 with factory 330 HP and probably not over 350 HP with the minor improvements I've made.

Being as in my typical use at 22 MPH and cruising under 30 MPH the noise is comparable or slightly less than driving my truck this is acceptable, but only barely. I'd imagine most folks would call it good enough. I'd like it quieter though. Given it's marginally acceptable I'm not going to cut the floor and install ski boat mufflers mid-season, but I may this winter. In the quest for a quieter exhaust I just ordered a pair of Gibson clamp on mufflers (https://gibsonperformance.com/i-2295...on-310001.html) to put on the tips behind the baffles. They don't show the internal construction or advertise a dB reduction, but they're short at 6.75" and might subdue the exhaust just enough. From the pictures it looks like a reverse louver that will splash some water around with the exhaust gas and make turbulence to muffle it. Worth a shot, hopefully they don't fall off. I'll measure dB in the driveway as well as on the water for comparison.

Love this thread. Great job on the specs.
However, my thought process works a little different than yours. The way I combatted the noise of the exhaust on my Sunsport 242 was to increase the decibel of the stereo system. Seriously.

At one point, I did think about FAE install but it has mixed reviews. Yes they work...when they stay attached to the boat. Referring mainly to aftermarket on older inboards.

Mufflers are cheap as I know several friends and family included that have had issues with them. My Sunsport 242, which has the ULTRA barrel style muffler, has now decided to implode. The baffles have come loose inside and it sounds like rocks in a washer machine. So, I'm going muffler delete using FAE straight pipes. I don't think it will make it any louder and I honestly love the sound of my inboards.

I'm at the lake...in an inboard...what's not to love about that sound?

My muffler is mounted in the engine dog house. 91 comp. silent muffler. Think it may be the only existing one that hasn’t had the baffles burnt out of it. It is quieter than most but at 22Mph has a hum that could drive you crazy too, so may not be for you. Just a different sound. Super quiet at slalom speed though and at idle really don’t hear it running. Will try and find picks.

Good point about FAE staying attached. I was also concerned about drag and force on the mounting brackets as I've read a few people have had issues with parts coming loose. I also prefer to hear that my engine is running, but I'll take silent or bubbly if I can't get there with mufflers. That's disappointing about the Ultra Marine mufflers failing (particularly on a newer EFI boat less prone to backfire), I got the impression they were a little better than Centek. It may come down to inherent weakness in any fiberglass muffler and luck of the draw. I've not found a stainless, long, small diameter ski boat style muffler. I think having the multiple partially water filled chambers is necessary to get a significant volume reduction. I considered straight turndowns but think they may increase noise in the boat and the rubber flappers probably have a similar but less pronounced redirection. The silent rider style muffler on the back of the engine would be an option if I could find one with 3.5" in and 3" out, and certainly easier than pulling up the floor, but I'm only found 3" in/out. I won't have room to fit the reducers on there for a 3" in.

I'm a lifelong gearhead and love the sound of a healthy V8, but as I get older I'm realizing hearing damage adds up over the years. My goal with this project is primarily to preserve what's left of my hearing. I have a few vehicles and have taken steps to quiet them all down and now wear earplugs every time I ride a motorcycle even with quiet exhaust, for wind noise. Hearing loss sucks and can sneak up on you over time.

Do these FAE's actually fall off? Run the Comp at 34/35mph everyday, while skiing, and it hasn't budged in 2.5 years. Have had it over 40mph occasionally.

The Gibson muffler tips arrived today. I don't expect a significant volume reduction from the straight through with baffle design, but it's similar to a glasspack you'd use on a car but using water instead of fiberglass to muffle the sound. They are very short at about 6-5/8" overall with only 3-1/2" beyond where they slide into existing 4" tips. They slide about 3" over the existing tips, and the inner baffle goes up into the tips 3-5/8". This means they won't fit the Hardin Marine tips with baffles installed as there is only 2-7/16" from the center baffle to the end of the tip. The slot where the two bolts clamp onto the tips is also too narrow to slip past the bolt holding the baffle into the tips.

I will modify these to fit by widening the slot to about 1/2" to clear the bolt holding the baffles, and cut down the inside inner baffle to 2-1/4" or less, maybe 2". This will result in 3/16" to 7/16" of open 2.5" exhaust (ID of inner baffle) at the end of the Gibson tip, plus the area of the louvered baffles. Much of the exhaust gas will have to make a 180* turn and the rest will go through the louvers mixed with water. I suspect this will result in fairly significant volume reduction and a much more effective muffler than either Hardin Marine Baffle or Gibson tip alone.

This may be the hot ticket to get it where I'm comfortable, though it may be too restrictive on the top end. If it is too restrictive at high RPM I will remove the tips and trim more from the inner baffle until performance is acceptable. Given the low HP per cubic inch of the PCM 454 I don't expect any significant performance change.

I've had my comp for over 35 years and tried many different ways over the years to quiet the rumble. The exhaust pipes are 3". So is a 2" glass pack. I got 2 -32" glass packs removed the guts. Took the baffle back to the muffler shop and had them flare the ends up to about 2 5/8 ". Raped the fiber glass back on the baffle and slid them into the 3" exhaust pipes. I know this is not Maurine and one would think that it would rust away but, 3 years so fare. The Ford sounds grate and I think it likes the little bit of extra back presser.

Very interesting about running glasspacks. I'm surprised they muffle well with the fiberglass saturated. Wet packing permanently reduces muffling performance on motorcycle mufflers, a problem when hosing down dirt bikes or on two strokes when the packing gets too saturated with oil. The constant flow of water probably makes up for it. I suspect 2" would be a little restrictive for a 454 though. Thanks for the details of your solution and experience.

I modified the Gibson mufflers today, shortening the inner baffle by about 1.25" (2" cutoff wheel on a die grinder) and widening the relief slot where they clamp on (3" cutoff wheel). I made a mistake measuring how far I needed to widen the relief slot for the bolt on the Hardin inserts, and did not wider the slot far enough. They are almost all the way on but seem pretty solidly on there and are clamped tight on both the bolt for the baffle and the pipe itself. I may lengthen the wider portion of the slot a bit to get them on farther. My other oversight was not realizing I needed to make a relief cut on the inner baffle to clean the bolt and nut inside the Hardin tips. I made this relief by cutting the baffle with a sawzall along each side of the slot for the clamp bolts and baffler bolt. I then folded the remaining inner edges of the baffle up (needle nose vice grips) to clear the bolt and nut for the Hardin insert.

The result idling in the driveway, measured same as before, 20' behind the boat and a few feet to the right is about 75 dB but spiked up to 76 dB occasionally and then in the driver seat is 72 dB. 5' behind the boat and a couple feet to right measures 82 dB.
No baffles: 87 / 77
Baffles: 81 / 72
Baffles+flappers: 81 / 72
Baffles+Gibson+flappers: 76 / 72

I'm very impressed with the muffling performance combining these two mufflers. It is very quiet at idle. I suspected this would be very quiet acting as a chambered muffler. I'm curious how it will perform on the water, I suspect noise reduction will increase with more water flow. If they perform as I suspect they will and they don't fall off, I think this will be the hot ticket for my needs. I'll probably be out tomorrow to test.

Tomorrow came 11 months later. I haven't used the boat at all until a couple weeks ago when I brought it to the lake house. I forgot my decibel meter, but anecdotally I'm thrilled with the performance of this muffler combination. It still has a noticeable rumble at idle and nice tone at wakeboard speeds, but is much quieter. Still louder than an I/O with exhaust under water but this setup is working for me and worth every bit of effort making it fit. Definitely easier than installing traditional fiberglass mufflers under the floor, which seem to have questionable longevity and can put a lot of water in the boat when they fail.