Through Transom Exhaust?

[Bigshrimpin]

I'm totally new to I/O's and trying to decide what to do about the exhaust. I got a nice freshwater Volvo 290 drive (non duo prop), the manifold didn't come with the deal, but I found a good one for short money. I'm wondering if it's worth it to route the exhaust out through the transom or if I should buy the manifold and route the exhaust out below the waterline. Any suggestions/advice would be greatly appreciated : )

[Water Rat]

Bigshrimpin,

I've got a '78 23' Sceptre with a 7.4L/Bravo 1 drivetrain that exhausts through drive itself. Unless you are trying to free-up horsepower with a less restrictive exhaust, I would recommend getting the "Y" pipe and exiting through the drive and underwater.

A couple of thoughts; one, this will be much more quiet especially at trolling speeds and two, you can always ditch the conventional, through-the-drive exhaust and go to a through-the-transom system in the future. My boat is very quiet at trolling/idle speeds. Starting with the conventional exhaust first, at least you are not cutting two 4" holes in your transom that you might regret later.

Would love to see this project sometime; please post pictures and good luck.

[FLexpat]

I have had it both ways and - like everything else - there are advantages and disadvantages to each. My 20 Bertram had a Volvo 290 w through hull just below the waterline and my 23 Sceptre had a Y tube through the drive (although it is all out during current rebuild). With the Bertram I needed it out through the transom since there was so little room (and I overfilled it); the well was designed for a 165HP I6 and I had a 290HP 5.7 V8 in it.

Through drive Pros:
quieter - especially for the neighbors and those in the boat following you
Factory flappers inside tubes usually work pretty well

Through Drive Cons:
Hard to tell if flappers inside the Y tube are not working well
hard to tell if you have corrosion issues on the Y tube in your bilges (unless you use a borescope or pull your engine periodically)
Another boot to maintain and that can be a PITA

Assuming the through transom goes out just under waterline - you probably don't want it above the waterline...
Through transom Pros:
Easy and cheap to maintain flappers since they are outside the hull
'Probably' easier to see all the fittings inside to inspect
Easy to tell which side of the engine you are having problems with (e.g. leaking valve stem seal)
Easier to hear when you are having a misfire - I heard it starting to slightly misfire on the way to Bahamas once and was able to get back to St. Lucie inlet just as the engine totaled itself
Less of potential leakpath to sink your boat (debatable)
Through hull cons:
Noiser in the boat and much noisier for folks behind you when you are on plane
Slightly noisier at low displacement speeds - noisiest at 'mush' speeds

Myths (my opinion)
I doubt there is enough of a performance difference to measure either way on a 5.7 but folks love to argue this
I doubt you raise the drive temp by running it through the drive unless something else is wrong - that raw water pump should be low pressure, high volume so lots of water does lots of cooling

I wrestled with the idea of putting it through the transom of the Sceptre now but am currently leaning towards using a Y pipe through the drive since I will probably pull the motor every couple of years for inspection and more importantly my wife does not like it loud at all - (marginally reformed ragbagger). I do like being able to hear the engine though...

[BigLew]

Hey BigShrimpin and Water Rat, you guys are less that forty miles apart. WR, you have the nicest/purest 23' scepter I know of and Big, well you just have a lot of everything and it is all nice stuff; plus you personally know and have worked with the "Rcon Guru" Strick himself. Consider this an introduction and one of you send a PM and set up a meet.for Heaven's sake!

[FishStretcher]

I have little to offer, other than being pleasantly surprised at how quiet a 5.7 is with a thru drive exhaust.

But FWC risers are money. I think the next motor will have etec vortec aluminum heads and no FWC. Or a big block

[Bigshrimpin]

Thanks Flexpat and Chris for the info. Chris . . . Come on down anytime. Just send me a PM. The Seafari is real dirty from sitting outside uncovered. I'm going to be pulling her into the garage sometime in March/April after I get the engine and drive ready to drop in.