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Neal Weatherman
#1 Posted : Tuesday, April 19, 2011 8:59:24 AM(UTC)
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My 1964 26' Single engine convertable was repowered in 1995 with a new Mercruiser bluewater small block Chev. 230 Hp. It has 4" dual exhaust from the engine to the thru hulls which are 2", the 4" hose has reducers inserted "inside" the 4" hose where it connects to the thru hulls.The boat did not have mufflers and I discovered this while installing new 4" Vernatone mufflers. The reducers are a square cut rubber 'doughnut". I have gone to some expense allready and wonder if I should go ahead bite the bullet and cut out the thru hulls with a 4" hole saw and replace them with 4" Centek fiberglass thruhulls, or is this really a problem? I am told that 2" is sufficient for this engine I just am uncomfortable with the way it is reduced. Your thoughts?
Thanks,
Neal
1965 26' Convertable, single screw, new 230 Hp Mercruiser w/ closed loop cooling, installed 1995, all systems upgraded 2004 to present.
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dougrose
#2 Posted : Wednesday, April 20, 2011 7:17:52 AM(UTC)
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I am no expert on engines, but personally I wouldn't even think about leaving that kind of obstruction. I am interested in hearing FastJeff's opinion.

if you make a wooden plug to jam into the holes you have, it will be a lot easier holding the holesaw since it will have a place for the pilot drill.


1975 32' Flybridge Sedan, twin Perkins 6-354 diesels, 1:1.53 velvetdrives, 16 X 19 props. Merritt Island, Florida
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Docsnow
#3 Posted : Wednesday, April 20, 2011 7:44:58 AM(UTC)
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Neal W.,

Myself instead off a hole saw I’d use a saber saw & cut out the determined size hole. One thing I found out about cutting aluminum with a power saw is to put a piece of wood like scrap paneling on the under side the wood backing for some reason keeps the blade from fouling & bucking.Anxious
AnyWho it worked great for me when I extended the swim platform & believe me there was a lot
of cutting to be done on that project.d'oh! Brick wall

Norm,

Big BigMs Live On Dancing
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 You'll have bad times, but they'll just wake you up to the good times you weren't paying attention to

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Neal Weatherman
#4 Posted : Wednesday, April 20, 2011 8:55:57 AM(UTC)
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What size exhaust was original on the Chryslers? was it same size all the way back?
Thanks Neal
1965 26' Convertable, single screw, new 230 Hp Mercruiser w/ closed loop cooling, installed 1995, all systems upgraded 2004 to present.
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Docsnow
#5 Posted : Wednesday, April 20, 2011 10:58:32 AM(UTC)
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Neal
On Mopar 318s & 360s the exhaust where both 4" from BigM manufacture at least from the 1970s
& earlier I’m not sure but the Jeffster can elaberate on that cause he’s a ole fart Dancing & knows all them older boat fact Jeezus he was Capt. Ahab’s cabin boy bet a lotta of U guys didn’t know that Shhh BTW he trained Sorry Dog & Joel TA DA the devil made me type this no it was 6 BREWSKI’s Dancing It's FIVE O'clock somewhere Think I Love JiMMY Applause

AB_Norm-al

Big BigMs Live On Dancing

http://www.picturetrail.com/gid23690601 Try it now there's music to listen to while U view the Big M's

http://www.PictureTrail..../index.php?clubID=20726 this one for the Pix club


 You'll have bad times, but they'll just wake you up to the good times you weren't paying attention to

Some people try to turn back their odometers.Not me, I want people to know "why" I look this way.I've traveled a long way and some of the roads weren't paved.
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ComputerJoe
#6 Posted : Wednesday, April 20, 2011 12:25:02 PM(UTC)
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Would like to see what a 26' convertable looks like...I believe my BigM was an Overnighter but then converted with side panels and RV windows. Looking for good ideas of what to do with her.

Thanks DOC, I know what the wood backing does, it cleatrs the teeth. Stupid me I had 6 blades and would switch them out then that night dig out the alu bits caught in the teeth. Seems to happen when the blade heats up softening the alu. Another way is to get some blade lube. I found some in a carboard tube...might have said drill lube but it worked the same way reducing heat up.
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ComputerJoe
#7 Posted : Wednesday, April 20, 2011 12:28:05 PM(UTC)
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Opps no edit.

I don't see how you could use a hole saw with a hole already there unless you backed it with something to center your saw with.
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Neal Weatherman
#8 Posted : Wednesday, April 20, 2011 1:34:01 PM(UTC)
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Thanks for the input guys, I think Norm is right about using a Sabre saw or maybe a rotary cutting tool. I am leaning towards 3" thru hulls with the proper reducer from the 4" hose. Hey Jeff! what do you think? is this restriction an issue or am I just fretting?
Neal
1965 26' Convertable, single screw, new 230 Hp Mercruiser w/ closed loop cooling, installed 1995, all systems upgraded 2004 to present.
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dependo
#9 Posted : Wednesday, April 20, 2011 2:06:48 PM(UTC)
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There was some talk about mufflers last year. Seems that that if you tilt the muffler up in the rear it trapps water deading the sound some.
Wayne
1973 express FB 32ft
twin 318
"Southern Lady"Chattanooga
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fastjeff
#10 Posted : Wednesday, April 20, 2011 4:23:48 PM(UTC)
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Going from a single 4 inch to a dual 2 inch is a bit too much restriction, and that hurts gas mileage and power. But going to two--4 inch outlets is overkill. A couple of 3 inch sure work fine.

Jeff
"...reality is not nearly as lovely as the world of Liberal Land. No wonder so many people want to go there." - Tom Sowell
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Neal Weatherman
#11 Posted : Wednesday, April 20, 2011 4:43:51 PM(UTC)
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Thanks Jeff, my current system is actually a dual 4" which is reduced to dual 2" at the thru hulls.
Neal
1965 26' Convertable, single screw, new 230 Hp Mercruiser w/ closed loop cooling, installed 1995, all systems upgraded 2004 to present.
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Docsnow
#12 Posted : Wednesday, April 20, 2011 5:00:31 PM(UTC)
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Jeff,

Get rid of that rubber ruler U use too save $$$$ it’s been 4"s since (& the Admiral will dispute that she claims 2" but 2 time 6 times a = 12) Exhaust has been 4” well maybe not from the 70s but newer 1s R 4" unless Cheap-Os have changed over OK enough of the bickering ask John A. what size muffler U need 4 your engine case settle Judge rules no dispute. John rule in my favor Jeffster will never let me live this down. If I’m wrong I got 4" hose that @ $ 8' won’t B worth a damn when I go 2 replace it wait I don’t own a BM AnyMO $hitt I miss the OTM & it’s my 1st no launch yr Oh well get over it Ab - Norm -al it ain’t gunna cost U $5.69 a gal 2 frolic but Norm $$$$ was meant 2 B spent Yup but I ain’t Jeff with canisters buried under the trees like him I've pix of all the cash he's buried but don't nose hows 2 post as of yet HELP!!Pray

Norm,

Going on 18 weathers terribbble can't even spell no mo O weel have a utter 1
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http://www.PictureTrail..../index.php?clubID=20726 this one for the Pix club


 You'll have bad times, but they'll just wake you up to the good times you weren't paying attention to

Some people try to turn back their odometers.Not me, I want people to know "why" I look this way.I've traveled a long way and some of the roads weren't paved.
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pfhlaw
#13 Posted : Wednesday, April 20, 2011 5:15:16 PM(UTC)
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Back pressure in an exhaust system can rob you of performance, but check your carburetor.
If it's a 2 barrel your current set up is probably ok. Not optimum, but ok.
Detroit produced millions of cars with V8s and twin exhaust pipes under 2" in diameter (but they didn't pump cooling water).
The original engine in your Marinette may have been a straight 6 or even a 4 cylinder with a 2 barrel.
Many older boats didn't have mufflers but used sections of oversized exhaust hose instead.
The restriction at the transom is intentional and required to reduce noise.

The standard chrysler V8 setup in Marinettes is a 3" hose from each side of the engine leading to a single 4" hose then into a muffler (4" in and 4" out) and a 4" through hull.
Peter
1981 32' sedan bridge
twin Chrysler 360 cu. in. 250 hp engines
Raw water cooled
Nimbus II
Home port: New Buffalo, MI
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Neal Weatherman
#14 Posted : Wednesday, April 20, 2011 5:35:33 PM(UTC)
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I'm gonna go with 3" thru hulls and use a hump hose reducer. She is sitting at my shop so nows the time to do it. I had her blasted and painted this winter so whats another couple a bucks right?
Many thanks fella's!
Neal
1965 26' Convertable, single screw, new 230 Hp Mercruiser w/ closed loop cooling, installed 1995, all systems upgraded 2004 to present.
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dougrose
#15 Posted : Wednesday, April 20, 2011 6:07:48 PM(UTC)
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If you reduce the size at the transom with a hose adapter, then all of the water in the pipe will not exit. This is OK I guess but most power boats use an exhaust sloped so that most of the water will leave. If it accumulates in there, it will spit out in bursts as the boat moves. It might be worth the slight extra expense and trouble to put in 4" thru the transom. And, if you decide to repower with a V-12 Jaguar some day, you won't have to change them. :-)


1975 32' Flybridge Sedan, twin Perkins 6-354 diesels, 1:1.53 velvetdrives, 16 X 19 props. Merritt Island, Florida
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Neal Weatherman
#16 Posted : Wednesday, May 18, 2011 1:17:06 PM(UTC)
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Just an update on my earlier exhaust thru hull query. I have finished installing new 3" thru hulls and flappers, ended up just drilling the old 2" ones out. Installed new 4" verna-ski mufflers. She sounds SWEET! still on the hard at my shop, doing strut and rudder bearings, new hoses and packing along with quite a few other items that I had been putting off till I got her back home (I'm still chasing a vibration) hope to be in the water again in 2 weeks. I do appreciate all the input guys.This has been pretty much a ground up restoration that I never would have started were it not for your taking time to share your experiences and expertise.

Neal
1965 26' Convertable, single screw, new 230 Hp Mercruiser w/ closed loop cooling, installed 1995, all systems upgraded 2004 to present.
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