Re: 4.3 to sbc question...
I already did this same swap in a 1986 Wellcraft Elan 197. Here is what I learned: 1- The motor mounts move 3". Mine were lagged into the stringers so I just filled the old holes and drilled new ones once the motor was in place, then re-lagged it with new bolts. 2-My alpha 1 gen 1 had 1.62/1 gears in it and I ran props from a 21" pitch 4 blade stainless Trophy to a 26" 4 blade Merc Bravo. With a stout 355 9-1 comp and edelbrock Performer rpm alum heads and intake, roller rockers 1.5/1, and a crane mild marine cam with 216* at .050" lift and .454" lift, I could over-rev the 21" prop even with three skiers out the back and a full load (people, gear and fuel) on the boat, there was NO plane time, the boat literally leapt out of the water and if you were turning 3500 rpm and floored it--it would press you back in the seat--hard! Top speed was 54 mph at a throttled back 5000 rpm. The 26" prop took a little more plane time--but not much-- and top speed was never noted, but was somewhat faster than the 21" and had a max rpm of 5100.
I then swapped the 1.5/1 alpha outdrive from my BIL's 260 hp setup and used a 23" Cleaver 3-blade. With just me in it, it hauled a lot faster than the 1.62's and the 26" prop, but with six people in the boat it struggled to get on plane and after about an hour running, we destroyed the upper gears. Turned out we sheared a few teeth off the ouput gear of the upper set. On a side note--I installed a set of heavy duty 1.5's in the drive for my BIL and he has run and is still running the drive with absolutely no further problems. My recommendation is to go with the heavy duty 1.5's as his original set was the regular duty versions and they failed. Another side note is the 1.62 drive is back on my boat and I put another few hundred hours on it tubing and skiing and have since sold it to a friend of mine who has beat the daylights out of it for the last two summers and it doesn't bother him to spin it with a 23" cleaver to 5600 rpm and it is still going strong. Draw your own conclusions.
If you go with the 350, the biggest advantage is the added torque--if you do nothing to the engine and keep your drive gear ratio and the same prop, you will have the same top speed you do now, but the boat will come out of the water much faster---then you adjust prop and gears to get the exact performance you want. The alpha will handle it with proper maintenance and a little common sense. They tell me the alpha shouldn't be spun past about 5000 rpm input shaft speed (eng speed).
Lastly, when you are figuring if it will fit in your engine bay, don't forget to take accessory placement into account--I thought mine would fit with no problem, but ended up having to clearance the engine hatch for the p/Steering pulley snout and belt.
Overall, the swap was well worth the effort and I would do it again in a heartbeat---but I swore i would never buy another I/O boat under 23 feet again and I never will.
--
Stan
I used to boat in the same body of water in 12'-19' boats with little trouble. But I have decided that I/O have too many disadvantages in smaller boats for my taste.