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Alright stern dudes I know this one will get debated but here I go.
I am looking at running through hull on a 1998 20.4 ft boat running 5.7GS(carb'd) with 1.5 gears in a cobra SX. My performance is 61MPH consistant and 63 with a half tank and no one else in the vessel. 21 SS PROP(a correction; I realized I posted 22 in another string) The boat runs great but I would like to get the most out of it with exhaust, carb, and looking at 1.6 ratio rocker arms. Is it really worth the money on an IMCO or stainless manifold or would I get the same performance gain with stock manifolds and direct through hull?
Will the IMCO or stainless give me the individual tube sound like headers give a car or are they overated on a -300HP boat set up?
Has anyone ran one of the electonic diverter swithes with stock exhaust manifolds? Was it worth the cash and performance gain and was the sound OK or just loud?
My only exit is below the power steering and so the electonic diverter doesn't look like it will fit because of the y pipes height is in the way of the exit. WIll running the pipes out below water level cause problems?
Lastly how do I get the Y pipe off or can I cut them down, leave it and cap the top?
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Hey neighbor,
I'll put my 2 cents in:
Originally posted by Mirage:
Is it really worth the money on an IMCO or stainless manifold or would I get the same performance gain with stock manifolds and direct through hull?
I went with EMI Thunder. IMO, stock cast manifolds are very heavy, so by switching, you will lose some weight right off the bat. However, through-hull is only one piece to the puzzle to make your engine flow better. The rockers are a step in the right direction, although a new cam would be even better. http://www.goldenplasma.f2s.com/foru...es/happy04.gif
Originally posted by Mirage:
Will the IMCO or stainless give me the individual tube sound like headers give a car or are they overated on a -300HP boat set up?...WIll running the pipes out below water level cause problems?
I installed Eddie 4" tips (w/internal flappers) under my swimsteps. They sound plenty beefy, but the "tube sound" is not there, mostly because my hatch is very insulated.
If you install a good set of heads, intake manifold, and cam down the road, the old stock manifolds would be the weakest link- goodbye!
I have no problems with the tips being below the water. They have the internal flappers to keep reversion to a minimum, and it's kinda nice to idle around with just some bubbles, and then it comes alive when it gets on plane. http://www.goldenplasma.f2s.com/foru...es/happy30.gif
Originally posted by Mirage:
Lastly how do I get the Y pipe off or can I cut them down, leave it and cap the top?
I had to pull the engine, unbolt the "Y", and make a plate and gasket to cap off the old exhaust exit (use the old bolt locations), and then I removed the bellows. Except for pulling the engine, it's actually pretty easy.
Good luck! http://www.goldenplasma.f2s.com/foru...es/happy25.gif
[This message has been edited by Havasu Hangin' (edited October 12, 2001).]
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I've got a 350 Mag EFI/MP with Bravo 1 and Rex Marine switchable cut-outs. There's no difference in performance whether the exhaust is diverted through the y-pipe and out the prop or through the thru-hulls. I use 4 inch pipes and stock exhaust manifolds. Sound is the only difference.
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Thanks Trash, Are the cutouts out of the water?, and is the through hull considerably louder at an idle and under way that prop exit? IE do you ever run it through the prop anymore?
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Mirage, if changing the exhaust is all that you plan on doing to the motor you probably will not see any performance gains.
As far as flow is concerned when running the exhaust out of the prop there is a large vacuum created (behind the propeller) and it helps to expediate exhaust out of the manifolds. The only thing that will help is weight reduction.
RD
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Has anyone ran one of the electonic diverter swithes with stock exhaust manifolds? Was it worth the cash and performance gain and was the sound OK or just loud?
My only exit is below the power steering and so the electonic diverter doesn't look like it will fit because of the y pipes height is in the way of the exit. WIll running the pipes out below water level cause problems?
Lastly how do I get the Y pipe off or can I cut them down, leave it and cap the top?
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When i had the stock exhaust manifolds with corsa switchable exhaust I lost around 4 mph if I left it cutout rather than through the transom. Still about the same with Stainless Marine manifold and roller rockers installed. It is very nice to cut the noise while idling through neighborhoods or cruising slowly listening to the tunes and having a cold one. As for what to do with the old exit. On the drive when it is in the trailer trim position find where the exhaust exits down to the drive. You can put a rubber cap on it with a hose clamp and some silicon and it seals fine. I had to do this on my old but when the original plate that blocks the exit started to leak. I didn't want to have to pull the motor for that. It was an OMC Cobra drive. Good luck, remember if you free up the exhaust and put the rocker in don't forget about the intake and get a K&N flame arrestor from Eddie Marine or someone.
Larry
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Do you have to remove the old y-pipe if you are just going off of the factory manifold. What happens if you leave it in there?
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If I leave the factory y-pipe in there what will happen???? TTT
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Originally posted by outtacontrol1:
If I leave the factory y-pipe in there what will happen?
If you don't block it off, I would think water can come back through it into the boat.
http://www.goldenplasma.f2s.com/foru...es/happy25.gif
PS- go ahead and make a new topic next time. http://www.goldenplasma.f2s.com/foru...es/happy06.gif
