Thru Hull Exhaust. Do it? Don't do it? Opinions?

I have a 1995 5.8Fsi (Ford Windsor Motor w/GT40 heads. Same as Ford Lightning trucks had). I've been itching to do a thru hull exhaust, as I really like the sound. I don't expect any real performance gain. Just a preference. Has anyone done this to their boats themselves? Pros/Cons? Is it better to ditch or cap off the Y pipe, or is a Capt.Call system better? Can the Y pipe be left in place and just capped off up high? Just wondering what i might be getting into. Any thoughts/suggestions would be appreciated.

Thanks!!

Ayuh,.... I did it 20 years ago, 'n have spent those 20 years tryin' to make it Quieter, ever since,....

No Way, I'll ever do it again to another hull,....

Been there done that on two different boats. I had two identical boats, 1969 Chris Craft Lancers ( over a period of 30 years) , that came with 185 hp 283 CID engines. Did thru hull with mufflers on both. On the second one, I went to a 260hp 5.7L Merc engine. The mechanic that did the swap declined to go thru hull, saying it not worth the trouble. As a result I have data BEFORE and AFTER thru hull. The MERC manual specifies either a single 4" exhaust or twin 3" exhaust. It also specifies maximum backpressure. I have a longish post on this that I will send to you if you want (pm your email), but the short story.... Thru a Volvo 200 series drive ( 250 or 280), the effective diameter ( as I recall) is the equivalent of a single 2 1/2 dia hole, a far cry from a single 4 or dual 3. I measured the back pressure as 6.5 psi, while MERC specified a max of 1.5 psi. My most recent conversion used a pair of fiberglass 3" dia mufflers. Getting them to fit in a stern drive boat is.... interesting. In the VOLVO pantheon of parts, there is a stainless steel dual muffler system that mounts on the back of the engine and vents out the transom. It's a big cylinder that sits sideways on the back of the engine, with 2 inlets and two 2 outlets. I do not have a part number or price or availability as I discovered this after I did my conversions. BTW, my MAX WOT RPMs increased by 450 rpms when I went to thru hull. With mufflers, my 280 drive boat is actually quieter "at speed" than thru the drive, since a 280's exhaust port is above water when the boat is on a plane.

RicardoMarine said:

The AQ series drives in 1995 (up to/thru the C-1 / C-2 drives) exit the exhaust via the lower unit housing, whereas the 1995 SX / DP-S Gimbal system stern drives exit the exhaust via center of propeller.

I believe that the Thru-Hull would render a bit more performance.
Salisbury offers an exhaust tip style muffler that appears to work well.

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When I did my last thru transom project 8 seasons ago, I tried to find Salisbury mufflers as I had used Salisbury in line mufflers to great success when I did my first thru transom project ( circa 1982). Could not find them. Not sure they are in business anymore. The exhaust tip ones appear with som e regularity on ebay as used.

re: "more performance"... Initially that is what I wanted as well until I measured the pressure in the exhaust line on my 280 and found it WAAAAY over max spec. Then it became an engine longevity issue for me.

RicardoMarine said:

The AQ series drives in 1995 (up to/thru the C-1 / C-2 drives) exit the exhaust via the lower unit housing, whereas the 1995 SX / DP-S Gimbal system stern drives exit the exhaust via center of propeller.

I believe that the Thru-Hull would render a bit more performance.
Salisbury offers an exhaust tip style muffler that appears to work well.

Click to expand...

Rick, the full number is 5.8FSIPHUCCE. This exhausts from the lower unit above the prop, not through the prop.

Thanks for the responses everyone. How does one measure back pressure, and find out what that back pressure should be on their particular motor?

Further your original post... Y pipe.. Mine was cut off a couple of inches above the "join". After wire brushing the inside and cleaning it, I coated it with life calk and then inserted a rubber plug ( the one with the "thermos" style lever seal) in each leg. I then filled the area above it with "life calk", let it cure and then installed neoprene caps over the ends with band clamps. A bit of a belt and suspenders approach. If you remove the Y pipe, you will need to block the thru transom shield hole. I think there is a Volvo part for this. otherwise you will have to fab a blocking plate. I removed the exhaust hose and installed a cork plug coated with life calk and a neoprene cap from the outside over the exhaust hose flange..( OK, I'm anal!)

Re: maximum exhaust backpressure.... The MERC Engine Installation manual for the engine had this number (2 psi). Seriously doubt that this number does not apply to all marine V8 engines. See below...

To measure exhaust back pressure I drilled a 1/32" hole at a 45 degree angle facing aft into the hose downstream of the elbow. I wet the end of a football inflation needle with soapy water and inserted it into the hole. I hooked up a tire pressure gauge that read down to 1 psi and started and ran the engine, at the dock and on the water ( a two person job for safety). When done I removed the needle. The hole eventually self sealed, while it "leaked" there were only a few residual soap bubbles. Drilling the hole at an angle encourages self sealing. I checked the tire pressure gauge with 20 ft of vertical clear plastic tubing marked every foot ( i.e. a DIY manometer) and a hand pump. The gauge was within 1/4 psi of the manometer readings. 1 foot of water = 0.43 psi.

UPDATE.... Found my original test notes..

"In Neutral... idle, 1000,1500 and 2000 RPM = <1 PSI
2500 RPm = 2.0 PSI
3000 RPM = 2.5 PSI
3500 RPM = 3.0 PSI
4000 RPM = 3.5 PSI

IN Gear... idle, 1000 and 1500 RPM = <1 PSI
2000 RPM = 2.0 PSI
2500 RPM = 3.5 PSI
3000 RPM = 5.5 PSI
3500 RPM = 6.0 PSI
3800 RPM = 6.5 PSI

Note these readings were taken with a 270 series "Y" pipe with only 1 bypass hole, not two for a total area of 6.1 sq inches. While the correct "Y" pipe has two bypass holes, its total area is only 0.78 sq inches more than the single bypass hole one. The difference between 6.1 sq inches and 6.8 is not enough to make a difference when it's supposed to be 12.5 sq inches! Going forward for me: Change exhaust to thru transom via mufflers (NJ state law) Advise to all... 5.7L engines should not
exhaust thru the leg on any drive up to and including 280/290. BTW... this is NOT a MERC vs Volvo engine issue. A 5.7L engine at 260 HP will flow the same amount of exhaust gas at a given RPM/extracted HP REGARDLESS of who made the engine. Exhaust scavenging (vacuum) from boat motion not enough to offset undersized exhaust port size."


View attachment MERC_INSTALL_MAN_86017501_EXHAUST SPECS.pdf

Great info Sandkicker. Arizona has the same law. So looks like it's time to find some mufflers.

Vessel operators may not hear sound signals or voices if the engine is not adequately muffled.

• All vessel engines must be equipped with an efficient muffler, underwater exhaust, or other effective muffling device that prevents excessive or unusual noise.
• A vessel operating on Arizona’s public waters must not exceed any of the following noise levels.
  • A noise level of 86 dB(A) when the sound level is measured at 50 feet or more from the vessel
  • For an engine manufactured before January 1, 1993, a noise level of 90 dB(A) when the stationary sound level test (SAEJ2005) is performed
  • For an engine manufactured on or after January 1, 1993, a noise level of 88 dB(A) when the stationary sound level test (SAEJ2005) is performed
  • A noise level of 75 dB(A) when the shoreline sound level test (SAEJ1970) is performed

I assume you guys are referencing tips like these with the mufflers in them? What have you made connecting pipes out of? I saw someone on another site say they used schedule 40 PVC because combination of water and air was not hot enough to melt it. That seemed kind of sketchy to me.

https://www.ebay.com/itm/CORSA-MARI...e=STRK:MEBIDX:IT&_trksid=p2055119.m1438.l2649

.... violates ABYC guidelines, which while it may not result in fines, will surely result in a no-pay situation by the insurance company if ever there is a problem. Any marine store and tons of on line sellers have "wet exhaust" duty hose. Many manufacturers make both marine exhaust duty elbows and 45 degree and other angle bend items made from both cast aluminum or special fiberglass. Since I had 4" ports on my elbows I used Merc 94444 cast elbows. It is a 4" to 3" x 76 degree elbow. ( 76 + 14 = 90 where 14 degrees is the MERC elbow down angle.) I could have used a 4" to 3" x 90 elbow, but I already had the 76 degree ones.

Chris Rohde said:

I assume you guys are referencing tips like these with the mufflers in them? What have you made connecting pipes out of? I saw someone on another site say they used schedule 40 PVC because combination of water and air was not hot enough to melt it. That seemed kind of sketchy to me.

https://www.ebay.com/itm/CORSA-MARI...e=STRK:MEBIDX:IT&_trksid=p2055119.m1438.l2649

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Chris, if you have the 5.8FSIPHUCCE model engine, the exhaust manifolds/elbows will look like this.

http://www.marinepartseurope.com/en/volvo-penta-explodedview-7797017-25-35437.aspx



Bob is correct..... you DO NOT want to use schedule 40 PVC pipe even while the exhaust is wet.

Your 5.8FSIPHUCCE exhaust "Elbows" should accept the correct ID soft-wall wet exhaust hose. Just make sure that the thru-transom exhaust tips are of the same OD as your elbows are.

If you place the the thru-transom exhaust tip outlets correctly, the hose should be able to connect the elbows directly to the exhaust tips.
Our USCG rules require either double worm drive band clamps at either ends, or single T-bolt clamps at either ends. Check with your regs!



.

RicardoMarine said:

Chris, if you have the 5.8FSIPHUCCE model engine, the exhaust manifolds/elbows will look like this.

http://www.marinepartseurope.com/en/volvo-penta-explodedview-7797017-25-35437.aspx



Bob is correct..... you DO NOT want to use schedule 40 PVC pipe even while the exhaust is wet.

Your 5.8FSIPHUCCE exhaust "Elbows" should accept the correct ID soft-wall wet exhaust hose. Just make sure that the thru-transom exhaust tips are of the same OD as your elbows are.

If you place the the thru-transom exhaust tip outlets correctly, the hose should be able to connect the elbows directly to the exhaust tips.
Our USCG rules require either double worm drive band clamps at either ends, or single T-bolt clamps at either ends. Check with your regs!



.

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Yessir, those are the ones. I would never do the schedule 40. Just thought it was worth mentioning what some folks will do. I'd be scared $hitless that the pipe would melt or crack on me. I'll be sure to measure and make sure that the OD of each is the same. Thanks!

To Capt. Bob's earlier point on backpressure....the 4" Hg (2 PSI) spec is common on all of the gasoline engines I've touched and the diesels are in the same vicinity-some higher nd some lower. Bottom line is the engine will be much happier with a backpressure lower than the max value specified. You would be surprised how many engines die a premature death from excessive backpressure in the exhaust system.....

re: "You would be surprised how many engines die a premature death from excessive backpressure in the exhaust system....."

Actually, no I would not. After taking those measurements, I figured that Volvo is only interested in if the engine will survive the warranty period... me... I expect 3000 hrs from mine ("FWC").

BTW... I have a glitch in the installation on my boat. As installed, since I had space issues, I have the exhaust routed outboard immediately after the engine's elbows thru the 4" x 3" reducer elbow, and then "down hill" thru Centek shorty mufflers and then immediately right angled out the transom above the water line within a few inches of the side of the boat. This works fine almost all the time. HOWEVER, I have a 22 degree deadrise deep V hull that can really dig in and heel over in a turn to the point where the outlet thru the transom can be higher than the elbow at the engine... The engine does not like this. Since this is NOT a normal thing for me and I do not operate the boat off shore, engine running in large beam seas ( the only "normal" situation that this can happen), its not been a problem other than just one time. After much head scratching, I have decided that a 2" OD aluminum pipe brazed into each of the 4"x3" reducer elbows and configured as a "cross over" ( two stub pipes and some 2" exhaust hose connecting them) should stop the engine from "complaining" in this admittedly unusual situation. I have the materials sourced ( another pair of elbows and 0.125 wall 2" aluminum tubing) and this spring will be making a pair of mating 4"x3"X 76 degree with cross over stubs. I'd do it this winter, except I lost the template that I made in order to set the angle correctly for the hole I have to drill in the elbows for the stubs and will have to wait until the boat is uncovered to remeasure it. ( the elbows angle downward to go to the mufflers, and the stubs for the cross over needs to be level to the engine. I no longer have ready access to a machine shop so drilling the 2" hole in the elbows and cutting the pipe at the complex angle needed for the junction, as well as machining a hose retention barb in the end of the pipe stubs, will be a challenge.

As always, great posts from all. I love this forum and appreciate all of your willingness to share your knowledge.

Reading Sandkicker's latest post, this brings up my next set of questions. I'm assuming I want the tips as far above the waterline as can be, but do I not also want them angled slightly down from the height of my elbow? How does one set these in the best possible position for success?

Chris Rohde said:

As always, great posts from all. I love this forum and appreciate all of your willingness to share your knowledge.

Reading Sandkicker's latest post, this brings up my next set of questions. I'm assuming I want the tips as far above the waterline as can be, but do I not also want them angled slightly down from the height of my elbow? How does one set these in the best possible position for success?

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Reread first page of the pdf attached to post#9

You need the 'drop' in the exhaust line, from the elbows, to comply the reference Capt Bob cited....the tips height above the waterline is set by that drop. If the tips aren't high enough for you, then you need to add risers under the elbows or adjust your expectations regarding the tips and the waterline.

The drop cited in the spec is the MINIMUM drop. While some boats have inboard exhaust outlets at or below the "at rest" laden water line, some designers set the minimum height relative to the laden water line with the lower edge of the exhaust port 1/2 times the diameter of the port above the water line. Flaps are a must.

Got it! Thanks again guys!! I'll let you know how it comes out.

You can flip the risers so they point forward. Then you plumb the mufflers in to this now-longer run of exhaust. The can tuck in to the side of the engine below the manifolds if there's room. Depending on your installation, you may wish to add spacers to the riser.

o2batsea said:

You can flip the risers so they point forward. Then you plumb the mufflers in to this now-longer run of exhaust. The can tuck in to the side of the engine below the manifolds if there's room. Depending on your installation, you may wish to add spacers to the riser.

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That is certainly an option.
However, with the type of "Elbows" that his Volvo Penta system is equipped with, if more Elbow height is required, he can add the Spacers/Risers underneath the Elbows without the need to reverse the Elbow direction.
In a single engine stern drive boat, reversing the Elbows and then plumbing the hoses rear-ward to the transom may consume quite a bit of space.

Just a thought!


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o2batsea said:

You can flip the risers so they point forward. Then you plumb the mufflers in to this now-longer run of exhaust. The can tuck in to the side of the engine below the manifolds if there's room. Depending on your installation, you may wish to add spacers to the riser.

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This is what I actually did the first time I thru hulled a ChrisCraft Lancer. Back then, I'd installed a Chrysler 318 @ 240HP and installed Salisbury mufflers directly at the transom inside the boat. Worked great although I had to dismount the mufflers to change the plugs. I wanted to do this on my current boat, however, the engine had too many things (chiefly the remote oil filter) inconveniently mounted on the front of the engine directly in front of the manifolds, hence the right angle out the rear and transverse mounted mufflers.

I don't have the room around the sides for that one. Wish I did. My engine compartment is not much of compartment. Everything is unfortunately very tight.

Okay guys, in looking at the back of my boat, it's a bit different than the diagram. On the diagram, you measure from the top of the elbow to the top of dimension "a", which I'm assuming is in line with the rubber bumper molding that runs around the boat. If so, the diagram shows the top of the elbow below this line. Mine is nearly 3" above this line. Here is a pic of the back, and what I'm looking at. I'm assuming that I need to do a+b = c instead of a-b=c. Sound right? Is fo my number is 18, and I
must be 13 or more. Also, I cannot drop my exhaust to "right above the waterline" as stated. I would need to remain a decent amount above. I have my power steering rack in the way. Any reason why I wouldn't run it up high underneath the rear deck? Thanks.

I'm assuming I want the tips as far above the waterline as can be, but do I not also want them angled slightly down from the height of my elbow? How does one set these in the best possible position for success?

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Back when I did the thru-hulls on my tin fishinm' barge, I used straight ssteel 4" pipe I had, striaght off the risers at the angle of the risers,....
They cleared all the important stuff, no cables or housin's in the way,...
Ended up several inches above the water line, 'n LOUD,....

Any reason why I wouldn't run it up high underneath the rear deck?

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Ayuh,.... So long as it's Downhill from the riser's tippin' point, down to the tips,...

It's 'bout the only choice ya got,....

At one time here in NJ, if the exhaust line is over some length ( 3 or 5 ft???, sorry don't recall) of exhaust duty rubber hose, they consider it muffled.