1979 20' ma 140 suzuki

[Bushwacker]

As I posted on another thread last Saturday, a 4-stroke motor generally needs about 30-40% more displacement to produce the same torque as a 2-stroke. I believe your 150 has the same 2.7L/158 cu. in. block as my E-TEC. That says the 140 Zuke needs to be at least 158x1.3 = 205 cu. in. to have roughly the same torque that you're use to with the old V-6, but it actually has only a 125 cu. in. powerhead, so it only has about 60% of the displacement it needs for the same torque! I.E., there's no substitute for cubic inches! If you'll PM me with an email address I can send you the torque/hp vs rpm comparison curves for the 150 E-TEC vs the 163 cu. inch 150 Yamaha 4-S. Even correcting for higher gear reduction on the gray motor, the smaller displacement E-TEC still has 23% more PROP torque than the gray motor at 3000 rpm where you're trying to get on plane!

Now the 140 Zuke is a fine economical motor and my favorite 4-stroke because it's relatively light and the chain driven cams and extra gear reduction appeal to my basic mechanical engineering instincts. The extra gear reduction lets it spin a large slow-turning more efficient prop so the 30-40% extra displacement rule might be overstated for it. It's no doubt pretty strong for it's size. However that 150 is a very conservatively rated (and thirsty!) motor with a VERY strong mid-range, and if it's propped so you can turn it up to about 5500 with your normal load, I suspect that Zuke is gonna feel pretty weak in comparison, although you could probably reduce your fuel load by 50%! Now if the V-6 has a lot more power than needed for what you're using, the Zuke might be acceptable. To get 140 hp out of only 125 cu. inches, it's got to have pretty high lift and large duration "hot rod" cams that make power at high rpm and sacrifice low and mid-range torque, so don't know how much of that you can offset with gear reduction. Since you're looking at older motors, you might look at the early 115 or 150 E-TEC's (2007 was the first model year for both.) Wet weights of the 140 Zuke and 150 E-TEC are nearly identical, but the E-TEC will be stronger than your current V-6, quieter than the Zuke at 30 mph and it won't burn that much more gas than the Zuke because you won't have to use so much throttle to get the same speed.