Exhaust Manifold Height

[mwilley22]

We have Mercruiser 502 in our 1988 Baja 265. We are getting different answers regarding the Exhaust Manifold height. We bought the boat with the motor out of it and we are not sure whether we should purchase a manifold spacer or not. From the end of the elbow to the end of the exhaust pipe there is 2 1/2" of drop. How we came up with it was we took a straight edge with a level on it and come up to 2 1/2" of drop. When looking into the exhaust pipe, there is equally a 1/4" space between the elbow and the rubber exhaust tube all the way around.

 

[Don S]

Re: Exhaust Manifold Height

Mercruiser says 13" minumum elbow height above the static water line. Keep in mind, that needs to be with your typical load on the back of the boat. A lot of people on the back of the boat or swimstep can bring that number down very quickly.
Here is a picture of how to measure it with a level. It's from Volvo, but gets the same measurement as Mercs method of clear hose over the side which is a real pain to do...

View attachment DPS Engine,Drive install manual 63.pdf

 

[tpenfield]

Re: Exhaust Manifold Height

Welcome to iBoats . . .


Since it is a Baja, I assume that you might be dealing with exhaust through the transom,
if so, you probably have something like this . . .

My engine has no riser (spacer) in between the exhaust manifold and the elbow. The Mercruiser elbow gives about a 7 degree slope to the exhaust tube, which is probably about 2-1/2" end-to-end, based on my picture.

So, I would say 'no separate riser' for your installation

 

[Don S]

Re: Exhaust Manifold Height

I didn't think about thru-hull exhaust, while the height restriction is still the same, there are other things to consider along with the height.
Here is an install manual that should cover any option.

Install Manual

 

[mwilley22]

Re: Exhaust Manifold Height

Thank you for the info. We don't think we have the stock elbows. The motor was in pcs when we got it so its been a long project. We have semi-tuned gast manifolds with stainless mercruiser used elbows. So we don't know if the stock manifold sits up higher or not then what we have.

Also, would you know if we need to time the motor or if it self-times itself?

Welcome to iBoats . . .


Since it is a Baja, I assume that you might be dealing with exhaust through the transom,
if so, you probably have something like this . . .

My engine has no riser (spacer) in between the exhaust manifold and the elbow. The Mercruiser elbow gives about a 7 degree slope to the exhaust tube, which is probably about 2-1/2" end-to-end, based on my picture.

So, I would say 'no separate riser' for your installation

 

[mwilley22]

Re: Exhaust Manifold Height

Thank you! We will look thru this manual you provided.

I didn't think about thru-hull exhaust, while the height restriction is still the same, there are other things to consider along with the height.
Here is an install manual that should cover any option.

Install Manual