Who has a 20 I/O?

Shadetree · #1 08-09-2003, 12:10 AM

Just wondering what kind of performance other folks are seeing on the 20 cc with the Merc 120/140 I/O setup. Banedog's 1970 has this setup(we think!)- the 4 cyl gm has had a valve cover swap, and we can't tell for sure what the displacement is without pulling the head and checking bore/stroke(no thanks!) I'm also pretty sure that the wrong drive ratio is in this boat, should be 2:1, I think it's more like 1.6:1, and I think it's over propped as well, came with a 13.75x21. Boat runs happily at 3000 rpm at about 24 mph, but maxes out at 3800 rpm. Book says it should run 4200-4600 w.o.t. Throttle plates are wide open @ full throttle. Timing is set to factory specs, no pinging, no overheating. I think the little 4 is tired, and have recomended a 3000rpm redline for longevity. We're gonna run the boat tomorrow with a 14x19 stainless prop, and see what it does. Anybody else have any thoughts or ideas?
Thanks,
Pat in MD

RIRED · #2 08-09-2003, 10:12 PM

I recently replaced my volvo with the 3 liter I/O Merc on my 20fter. I usually cruise at 3300-3500rpm = 23knots. 4000 rpm = 26knots. At 4800rpm =32knots.

jw · #3 08-26-2003, 09:34 AM

Pat,
I have a 1975 20fter CC with the 140 MC. It is now in pieces in my shop waiting for cold weather to finish the rebuild process. I did run her last summer, played with the props, I have the right prop in my shop, cannot remember what i went with , I will have to get back to you on that.Do you have the original out drive with the ring on top of it? I think they outdrives were 2:1 the 19" prop will get you close but for some reason I keep thinking 17" inch pitch. I will let you know.
JW

Shadetree · #4 08-26-2003, 05:39 PM

JW- this engine/drive setup we have here is a hodgepodge of parts from different years, thats why I'm having so much trouble figuring out what I should expect out of it. It has a relatively new Alpha Gen II drive on it, but an older transom assy.(the shift arm in the bellhousing has been modified to work with the gen II). All the 120/140/3.0 should have either 2/1 or 1.98/1 gears, but I didn't check when the drive was off the boat. The drive will be getting new U joints soon, so I'll check the gears then. Given the fact that I think the engine is real high time, I wanna keep cruise at or below 3000 rpm for longevity, and would like to get 22-23 mph out of the boat at that rpm. Let me know what you find out on yer prop, if ya remember.
Thanks,
Pat