My apologies, I thought you were asking me if the 2.5 sportjet was vertical. If possible to swap the 3.0 or 4.3 liter would be installed horizontal. There is already plenty of cutout space to fit the 3.0. I'm just trying to figure out if the either one of these motors will bolt to the jet propulsion unit. I have no experience in this area.
Quick answer, if a horizontally installed engine with a horizontal out put will "bolt" onto the existing housing which has a vertical input shaft, NO
But if you are considering a horizontal install then change both your pump and jet. You did not specify the horsepower of your 2.5 and also did not say how long your boat is.
I believe that Kodiak in Washington? still probably makes a V-6 with one of their 2 stage pumps. There would be others of course. The 2.5's were noisy. But proper sound attenuation processes can reduce this immensely
I am not a fan of the sportjet pump. We had an occasion to be over a hundred miles up a river in northern Canada many years ago and a group of 3 people were in an 18 foot boat with a sportjet and they were unable to get the
boat on step to be able to run some shallow rapids. After many attempts their guide put a large log on the beach, pegged it in and ran the boat up over the log to get the stern and pump out of the water. As we were camped on the same sand bar,
we saw the guy pull the rear of the pump off and remove a willow branch that was perhaps 8 inches long with a 1/2 inch diameter that had got sucked into the pump.
They have advantages, weight is one. Noise, is a disadvantage but probably not much different than the old Hamilton 773.
Yellowjacket pinned it regarding what you will gain if anything in the performance end without changing impellers to take advantage of a different rpm/hp range.
A solid sound abatement program, say 1 1/2 inch Soundown, two layers of acoustic foam, decoupled with high mass layer between, with a mylar finish will take care of the inside of the engine cover. Some upholstery on top of the cover will help as a second layer.
You need to make the engine space tight so that noise will not escape. So if you have floor boards, you need to bulkhead between them and the hull. The installation of pipe limber holes about 18 inches long and 2 inches in inside diameter
about 6 of them packed with stainless steel mesh, ( like a pot scrubber) will allow water movement and some intake air. A couple of clamshell vents on the transom but at the very top of the transom to supply further combustion air to ensure some more cooling air baffled as well, and you will have as quiet as boat as you will get. Also you will have blowers for the engine compartment, you can baffle these a bit but I would add another and leave it run when your the engine is running.
Ie key on, one blower on
