Mercruiser Risers for OMC Engine

[jeromeb]

First, Hello to all,

I am new to the site and new to boating. I just bought a "mechanic's special". It is a 1986 Sea Ray 21' Seville Cuddy. It has a thoroughly locked up 4.3 engine with Cobra drive. While new to boating, I am well versed in automotive repairs. I made my living for more than 40 years repairing cars, trucks, gasoline and Diesel.

That said, this 4.3 has the infamous "batwing" risers. I don't know if they contributed to the current engine locking up but I want make sure that the replacement engine doesn't suffer the same fate. What I have noticed is that risers for OMC engines are much more expensive than those for Mercruiser. OMC no longer in production and Mercruiser still turning them out is more than likely the reason.

I will buy new OMC replacements if necessary but has anyone successfully attempted to swap Mercruiser risers to an OMC engine? From what I see, the engines are virtually identical and adapter bellows, (if there is such a thing), would connect them to the Y pipe. Is this a "pipe dream" or is it possible?

 

[Lou C]

Re: Mercruiser Risers for OMC Engine

There is an aftermarket conversion available for the batwings which you can't get anymore. I have the bat wings on mine and I don't think they are bad at all, as long as they are in good condition. Mine started clogging after 5.5 seasons in salt, I had a new pair that I bought some years back so I istalled those. Do a search for OMC V-6 conversion manifolds, it's pricey but the right way to go for a new engine. There may be one with GLM manifolds and one with Barr or Osco, I'd go with those instead of GLM. Here's mine both new and after 5.5 seasons....there was no rust or sign of water in the exhaust passages or on the exhaust valves either, this boat is slipped in salt 6 months and only flushed at the end of the season....

here it is....
http://www.go2marine.com/product.do?no=153929F

 

[jeromeb]

Re: Mercruiser Risers for OMC Engine

I appreciate the fast comeback. The thing that bothers me is the "/won't fit vortec engine". It clearly state Vortec on the valve cover of the current engine and also on the replacement engine. Are there 4.3's that aren't vortec?

 

[Lou C]

Re: Mercruiser Risers for OMC Engine

the Vortec is a different head design, I think they came into use around 1996 or so, if your new engine is a Vortec, then I'd do some more research. It may be that the Vortec is more prone to pulling water up the exhaust than the original head design. On the newer OMC 4.3s, they changed from the batwings around 91 or so, to a 2 piece design, like that conversion kit. I wonder if you could use the later model OMC/Volvo exhaust, on your present Y pipe. This newer design was also used on the Volvo 4.3s with the SX drive starting in 94. The only other thing I can think of, is to change the Y pipe to the later style used after 91, go over to www.dougrussell.com and check parts #s to be sure on what was changed, and when....

 

[jeromeb]

Re: Mercruiser Risers for OMC Engine

Thanks a bunch. You've given me a direction to follow.

Jerome B.

 

[Jason89sunbird]

Re: Mercruiser Risers for OMC Engine

I just got my 89 4.3 cobra sterndrive running. It has vortec heads and merc manifolds and 3" risers. I bought the boat with the merc setup already on it and the connection pipe to the y pipe is mickey mouse to say it nicely. This winter I plan on building a 3" mandrel bent connector pipe since I work at an exhaust shop, I am the driveability mechanic their.. the bat wing manifolds dont fit the plastic vortec valve covers properly. A true vortec engine has 8 intake manifold bolts instead of 12. You can run non vortec, center bolt valve covers on vortec heads so the batwings can fit.

 

[jeromeb]

Re: Mercruiser Risers for OMC Engine

I just got my 89 4.3 cobra sterndrive running. It has vortec heads and merc manifolds and 3" risers. I bought the boat with the merc setup already on it and the connection pipe to the y pipe is mickey mouse to say it nicely. This winter I plan on building a 3" mandrel bent connector pipe since I work at an exhaust shop, I am the driveability mechanic their.. the bat wing manifolds dont fit the plastic vortec valve covers properly. A true vortec engine has 8 intake manifold bolts instead of 12. You can run non vortec, center bolt valve covers on vortec heads so the batwings can fit.

Thanks,
I learn a little more everyday.