Ben, Please know that we're only here to express our thoughts of how we know the mercruiser system is designed to work for best use. Also for the most part as an safety caution to you, this forums intent is only going to give you our take of the correct procedures that in our opinion should be followed. Granted some mileage may vary of what works and what don't, it seems you're going to/planning to be in the category of finding out different ways of trying to make things work that might not ordinarily work for others.
You are correct that Merc used alphas with some of the lower HP diesel engines.
Diesel Drives
Alpha One[SUP]®[/SUP] Strong. Versatile. Reliable.
- Available for single and twin engine applications, the Alpha One’s efficient hydrodynamic profile produces very little drag, which means better boat performance and fuel economy.
- Features like an integrated water pump and permanently lubricated pivot points let you spend less time on maintenance and more time boating.
- Designed for boats capable of up to 65 mph and gas engines delivering up to 300hp and diesel engines up to 150hp.
There's a few ways to think about not having/utilizing a split second engine hesitation during shifting out of gear. Its purpose is to unload the gears in the drive to make shifting easier plus depending on what type of load you have on the engine/drive setup which may include boat weight/size as well as engine torque and propeller type used, shifting could be much more difficult and unsafe.
For whatever reason the dealer decided to remove your OEM shift interrupt system really wasn't the best choice for them to make even though it may have seemed to work for you. Under typical circumstances removing it should have made shifting a little less desirable on you even if you became used to it. Plus the fact that should there had been an accident of major concern, the lawyers would have hired a professional marine surveyor who would have found that system not working/missing and the dealer would be on the hook for that mishap. Don't ask me how I know this as that is another story about the shifting system and lawyers.
Being that you had a 3.0l probably on a lighter weight boat model with I'd guess an aluminum propeller you might not have notice the shift interrupt system not working as much if say you had more HP of a V8 running a stainless steel propeller on a heavier boat model per say.
During on the water shift interrupt testing that I have done in the past, I can honestly say with the 350 V8 stainless propeller combo, shifting was near impossible at times when I had to disconnect the shift switch.
Though the bigger engine coupler used on the diesels vs the gassers might help absorb some of the engine torque not to bother the alpha drives as much as one might think, I can't help but think that the extra torque of the diesel "might" play into affect on the shifting being an extra load on the gears to where your going to need the interrupt system for your shifting safety. Again your mileage may vary but at least your preparing or prepared for it should you open mindedly need it.
A final note about discrediting Scott's theory above about the heat exchanger and water flow. If there's anyone on here that knows about heat exchangers and their flow capacities and what your trying to accomplish, Scott is definitely going to be at the top of list due to he spent many years working as an engineering designer/tester for one of the big name marine heat exchangers manufactures so he definitely knows what their capable of doing or not doing.
While I have heard of some removing the alpha impeller and being ok as far as heat, it's a much better idea to leave the impeller in to get more drive cooling. The nice thing about the alpha gen 2 impellers are, if ran in clean waters and not run dry, the OEM impellers have been know to last 7-8 years + and still look like near new when removed for replacement. Just something to think about while trying to decide if your going to run one or not.
One other theory mercruiser asks you to do is, since you're going thru-hull exhaust, they say to remove the exhaust bellows between the bell housing and transom assembly due to you could develop a vacuum at the propeller that could affect overall boat performance.
Whatever way you decide to go, good luck and be sure to update the topic with the outcome of it all.
