I'm doing a 90-140 HP Johnson V4 conversion. Some people say thats a bad idea and I wont notice a difference. That sort of talk give me blank stare syndrome. I've been behind the wheel of a few 140's and the 90's are nice engines down low but really run out of steam on the top end. I want top end. No, it's not cheaper to buy a 140.
Ive done some shopping around spent money good some places and not so well other places. Basically I'm out to build a 140 . Heres what Ive got
1. A 1981 standard bore 115 block. Some people say they are the same as 140. Some say they are not. No one will give me any specifics on port size so I guess I'll keep looking for actual port dimension or I'll just port the 115 block the best I can figure out . A little smoothing and polishing here and there. No scoring or anything in the block and the bores arent out of shape or egged. Nice block for $80. A hone job on the block and I can reuse the 90 HP internals ie pistons and rods, crank etc. new rings , yada , yada, yada.
2. Boyesen reeds and a little porting on the intake. I guess I could use the stuffers but I don't feel like buying any especially the cheesy plastic OMC ones. . I'll just machine some out of UHMW stock.
3. My 90 HP actually came with 1 5/16" carbs and 65c main jets. Yeah I was surprised and they are originals. My dad was the original owner and he has never had them off the engine . Anyway, I picked up a set of crossflow V6 175 XP carbs with 1 3/8" throats that I can adapt to the V4 intae ( 2 of them anyway ). I'll try it with both. Ive got a decent accelerometer and 1/4 mile testing is the most accurate gauge of HP even on the water. I don't expect I'll see a difference at 5800 RPM between the two carb sets.
4. I picked up a bubble back exhaust manifold set for for $40. I'll likely cut out the lower ribbing out and smooth transitions but the stuffers seem to me to be designed more for mid range velocity and power than top end and all that Ive seen about them from people who have left them out is showing me that
5. Heads. Ive got a great set from a 1976 85 HP engine. $30 . The chambers are MUCH smaller than the 90HP motors heads. I'm targeting 135-140 cranking PSI and I'll machine the chambers accordingly. I know 85's had smaller bore but the 90 HP piston domes clear the chambers . Yes. It means premium real gas.
Any constructive comments or suggestions for more power. It will use more gas. I know. Right now I can hit 49 MPH GPS with the 19 pitch 3 blade SS OMC prop at 5800 RPM. The charts show a 6% slip which is reasonable. My 17 pitch 4 blade SS Solas goes 44 mph at 5300 . According to the prop slip calculator that is as close to 0% slip as is possible if not impossible meaning that cupping makes it a bit more than a true 17 inch. I'll probably pick up a 23 pitch 4 blade Solas. with a little more power I should nail down 60 with no problem. Is it worth tearing down a good 90 to build a Frankenstein 140. It is to me so thats what matters.
Ive done some shopping around spent money good some places and not so well other places. Basically I'm out to build a 140 . Heres what Ive got
1. A 1981 standard bore 115 block. Some people say they are the same as 140. Some say they are not. No one will give me any specifics on port size so I guess I'll keep looking for actual port dimension or I'll just port the 115 block the best I can figure out . A little smoothing and polishing here and there. No scoring or anything in the block and the bores arent out of shape or egged. Nice block for $80. A hone job on the block and I can reuse the 90 HP internals ie pistons and rods, crank etc. new rings , yada , yada, yada.
2. Boyesen reeds and a little porting on the intake. I guess I could use the stuffers but I don't feel like buying any especially the cheesy plastic OMC ones. . I'll just machine some out of UHMW stock.
3. My 90 HP actually came with 1 5/16" carbs and 65c main jets. Yeah I was surprised and they are originals. My dad was the original owner and he has never had them off the engine . Anyway, I picked up a set of crossflow V6 175 XP carbs with 1 3/8" throats that I can adapt to the V4 intae ( 2 of them anyway ). I'll try it with both. Ive got a decent accelerometer and 1/4 mile testing is the most accurate gauge of HP even on the water. I don't expect I'll see a difference at 5800 RPM between the two carb sets.
4. I picked up a bubble back exhaust manifold set for for $40. I'll likely cut out the lower ribbing out and smooth transitions but the stuffers seem to me to be designed more for mid range velocity and power than top end and all that Ive seen about them from people who have left them out is showing me that
5. Heads. Ive got a great set from a 1976 85 HP engine. $30 . The chambers are MUCH smaller than the 90HP motors heads. I'm targeting 135-140 cranking PSI and I'll machine the chambers accordingly. I know 85's had smaller bore but the 90 HP piston domes clear the chambers . Yes. It means premium real gas.
Any constructive comments or suggestions for more power. It will use more gas. I know. Right now I can hit 49 MPH GPS with the 19 pitch 3 blade SS OMC prop at 5800 RPM. The charts show a 6% slip which is reasonable. My 17 pitch 4 blade SS Solas goes 44 mph at 5300 . According to the prop slip calculator that is as close to 0% slip as is possible if not impossible meaning that cupping makes it a bit more than a true 17 inch. I'll probably pick up a 23 pitch 4 blade Solas. with a little more power I should nail down 60 with no problem. Is it worth tearing down a good 90 to build a Frankenstein 140. It is to me so thats what matters.
