Re: Throwing in the towel
No wonder OMC went out of business
Using a large port manifold on a small port head (or the other way around) is asking for problems. Get a manifold with the correct port configuration or use a head that matches your manifold.
That adapter plate would most likely cure the vacuum leak, but it's still not going to perform as well as a properly matched head and manifold. I wouldn't do the adapter plate as you will be killing performance. The $150 adapter is almost the price of a new manifold.
Be aware, some of the manifolds have a different carb bolt pattern and bore spacing,,, Rochester carb compared to a Mercarb. I'm not sure, but would almost bet that any "high performance" manifold with the smaller intake ports is going to be setup for a Mercarb, instead of a Rochester carb. (correct me if I'm wrong on that one...)
This type of mismatch problem comes up a couple times a year when someone is trying to swap around 2.5L/3.0L/120HP/130HP/140HP/ parts from different years. Even though the 4 cylinder GM marine engine has been around for 40+ years, not all parts are swappable. Then going from OMC to Mercruiser...
No wonder OMC went out of business
Using a large port manifold on a small port head (or the other way around) is asking for problems. Get a manifold with the correct port configuration or use a head that matches your manifold.
That adapter plate would most likely cure the vacuum leak, but it's still not going to perform as well as a properly matched head and manifold. I wouldn't do the adapter plate as you will be killing performance. The $150 adapter is almost the price of a new manifold.
Be aware, some of the manifolds have a different carb bolt pattern and bore spacing,,, Rochester carb compared to a Mercarb. I'm not sure, but would almost bet that any "high performance" manifold with the smaller intake ports is going to be setup for a Mercarb, instead of a Rochester carb. (correct me if I'm wrong on that one...)
This type of mismatch problem comes up a couple times a year when someone is trying to swap around 2.5L/3.0L/120HP/130HP/140HP/ parts from different years. Even though the 4 cylinder GM marine engine has been around for 40+ years, not all parts are swappable. Then going from OMC to Mercruiser...
