converting to thru-hull exhaust, pointers??

[workaholic]

I am in the process of dropping a new rebuilt 350 in my boat (replacing an old 283).. The boat has the old stringer outdrive... I would like to convert to a thru hull exhaust.. Can i just simply reroute the 2 hoses coming from the exhaust manifold elbows to go out the back of the hull and not down into each side of the middle drive unit?? then just simply cap off the 2 inlets (1 per side) of the middle drive unit (so the water doesnt come in the boat)??

How about heights and elbows??

 

[greg82255]

Re: converting to thru-hull exhaust, pointers??

Yes on all counts. The risers should be at least 13" above the water line. Also make sure the exit point (transom tip) is lower than the riser so the hose is angled downward, which keeps water from flowing back into the engine. Also make sure you have either internal or external flappers on your exhaust tips. Capping the Y-pipe is easily done with some pipe caps from home depot or your local plumbing supply store.

Not sure what your goals are, but if you're doing this hoping to gain some power, it's not going to happen. I did the same thing a few years ago hoping to gain some power and all the experts in these forums said it wouldn't happen. I believe it was Bondo that said "Thru-hulls add Noise, not Power..."

 

[workaholic]

Re: converting to thru-hull exhaust, pointers??

Just going to thru-hull for sounds and looks, thats all..

I have the old log style manifolds (no center risers)... so do I just continue the drop off the elbows then straight out of the just above the water line??? I am assuming the flappers will help block the water from entering when I throttle down and the wake reaches the back of the boat, correct?

 

[Bondo]

Re: converting to thru-hull exhaust, pointers??

Ayuh,... Log manifolds aren't very conducive to thru-hulls, as the risers are pointin' the wrong way...
And, you don't have the drop, in inches, as center risers...

 

[greg82255]

Re: converting to thru-hull exhaust, pointers??

I think it would make much more sense to switch to center-riser manifolds before you go to thru-hulls. On log manifolds, the risers are much closer to the water line - you don't have that 13 inch gap that you need. Plus it will be very difficult to fit a 90 degree elbow turned toward the transom under those risers. The only way to get around the Y-pipe would be to remove it, which is a real pain (need to pull the motor). But still, if you throttle down too quickly with that setup, you will end up with much bigger problems.

I'd vote for center risers, or to keep what you have. Some people say the noise of thru-hulls gets annoying after a while (although I've been running mine for 2 seasons now and still love waking everyone up on the lake just as much as I did at first).

 

[workaholic]

Re: converting to thru-hull exhaust, pointers??

If I go with center rise manifolds, will they just bolt up to the 350 block i just ordered (its a 1978 block, fully rebuilt)... Are they the same bolt pattern as my old log style i had on my previous engine (it was a 283ci)??

 

[AZSenza]

Re: converting to thru-hull exhaust, pointers??

Yes, same bolt patterns. I dont know how different the sfift/throttle brackets are though but anything can be worked through. I had Thru Hulls on my 85 4 Winns and LOVED 'em. Some day I'll get em on my Larson!