1979 260 weekender what ratio and prop should i run

I guess this might be a thread hijack of sorts but it's related so I didn't want to post another thread. My only recent experience before my current 260 was a '78 SRV-195 (OMC 800, 5.7l OMC 230) and I had a hard time getting that boat to 40mph (checked with GPS). However, my new '83 I haven't had above 3500 RPMs (about 75% throttle) yet and at 3500 I was running 36.8mph at 5000 feet altitude, trim tabs all the way up and the outdrives trimmed right in the middle. It is a twin OMC V6 setup with 15x17 aluminum props but I was very surprised at the increased performance of the 26' twin over the 20' single. Now I'm seeing people talking about max speeds in the 27 to 30 range (with single engines) and really starting to wonder why my boat seems so much faster.

P.S. Sorry - edited the typo (should have been 36.8 not 46.8)
 
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SJAurora said:
I guess this might be a thread hijack of sorts but it's related so I didn't want to post another thread. My only recent experience before my current 260 was a '78 SRV-195 (OMC 800, 5.7l OMC 230) and I had a hard time getting that boat to 40mph (checked with GPS). However, my new '83 I haven't had above 3500 RPMs (about 75% throttle) yet and at 3500 I was running 46.8mph at 5000 feet altitude, trim tabs all the way up and the outdrives trimmed right in the middle. It is a twin OMC V6 setup with 15x17 aluminum props but I was very surprised at the increased performance of the 26' twin over the 20' single. Now I'm seeing people talking about max speeds in the 30 to 36 range (with single engines) and really starting to wonder why my boat seems so much faster.
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WHOA!!! 46.8?? never heard of a 260 running like that. Is the bottom painted? Did the previous owner put some Clark Griswold toboggan polymer on the bottom? My boat is a little different from yours but I believe that from the rail down its very similar and the best I've ever gotten is 37 but I have a single 350. I know someone in my marina with an 85 270 that can get to 40 with twin 185 v-6's but thats still kinda rare. Be happy cuz youre gonna get there and burn less fuel.......but...on that note I would double check your tach to make sure its registering right cuz 46 at 3500 just sounds otherworldly.
 
Jason, Sorry, I edited my post to fix my typo just after you replied I guess. It was supposed to be 36.8 not 46.8, but both tacks were at 3500 on the nose (not likely they would both be off). I still had at least 25% of the throttle left to go and the engines weren't bogging at all. I'm guessing at WOT that's going to put me close to 42mph anyway. The bottom is painted - it's a really ugly rust brown color though. I have the original Quadrajets on the engines and fairly low hours (I think). My gauges are showing 411 hours on the port engine and 600 on the Starboard engine - not sure why there is a difference since they both appear to be original.
 
Those are good numbers SJ. They make sense to me. Your twin V-6's combined have to put out more HP and Torque then our Single 350's and I can top out at 37ish. 42 seems very realistic.
 
BillyT0020 said:
Those are good numbers SJ. They make sense to me. Your twin V-6's combined have to put out more HP and Torque then our Single 350's and I can top out at 37ish. 42 seems very realistic.
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Yes...much more realistic now.
 
Billy your numbers and performance seems great almost to good to be true.
I thought my 79 260 with a 350 had a alpha one but after reading your posts I'm second guessing it. What drive was on your boat originally?
 
I originally had the pre-alpha, it has a hook on the top of the gear plate that they used to use to lift the drives, the alpha one is flat on top. That shouldn't provide any additional performance increase, but they are rated up to 300 HP and don;t have the pre-load pin that was prone to fail. I did lighten my boat a little by replacing the 100 gallon aluminum fuel tank with a 50 gallon poly tank so at full fuel im about 400 pounds lighter then you and all my cylinders are still over 150 psi so I don't know if this engine was ever rebuilt as it has over 1100 hours on it. The boat performs really well with only 2 people on board with the 17p prop but slows down in a hurry as soon as more people get on. Im going to try the 14.5 x 15p cupped SS this weekend to see if it handles extra weight better but im sure the top end speed will suffer some. I'll let you guys know how it goes. Overall Im happy with her for now, but cant wait to get the 496 stroker engine im building in her:thumbsup: It will be a couple of years but the engine will be close to 550 HP with over 600 lb/ft of torque:smt038
 
Sorry Guys, no info on the 14.5 x 15 (cupped) Merc Vengeance SS Prop. I tried it this weekend but it has a spun hub. No go over 1700 RPM's. I wanted to try it because I had some extra people onboard this weekend and the 17P prop really is best when its just the girl and me with little to no chop, but I had to use it regardless.
 
Hey guys just wanted to give you an update on some new numbers I got. I was doing some maintainence this past week and switched my points over to pertronix electric ign. WOW! I dont know what took me so long. I also decided to get some numbers with both my 15.25 x 15 prop and my 16 x 16. I got my boat with a 17p and it was a dog so i switched to a 16x16 and it was a huge improvement. I then got the 15.25 x 15 cuz it was said to be the factory spec prop. It also gave good performace but I never really ran the numbers for the two. Well after some swapping I can say that for MY boat and I'm sure others like it.....the 16x16 is the way to go.

3000 rpm 17mph with 15p 18.8-19 with 16p
3200 rpm 20/22
3600 rpm 25/28
4000 rpm 28/32

I jump out of the hole, cruise real easy and never lose bite. These are just my two cents but after playing with three sizes. The 16x16 is the best, hands down. I even loaded the boat up with firewood and stuff for camping out and we had no issue planing or holding plane.
 
with all this prop talk and me knowing nothing about boats my old boat is a 20 footer with the 260 merc 350 my gears im guessing is a 1:50 and I bought a 21 pitch stainless for 75.00 in perfect shape. does anyone know about what this boat should run or should I even use the prop I have.
 
Matt89GT said:
with all this prop talk and me knowing nothing about boats my old boat is a 20 footer with the 260 merc 350 my gears im guessing is a 1:50 and I bought a 21 pitch stainless for 75.00 in perfect shape. does anyone know about what this boat should run or should I even use the prop I have.
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I dont know much about that boat but I've never heard of anyone running that sized prop with the 350. The best prop for your boat is the one that puts the motor within its optimum running limits. The Carbed Merc 350 has a best cruise rpm of 34-3600 and a WOT of 4600 max. Your boat should reach between 4200-4600 rpm at WOT which will give you hypothetically a three prop range of options. Each prop is worth 200 rpms per pitch. So 15x15 =4600, 16x16 = 4400, 15x17 = 4200. As long as your engine is running right, you'll never go wrong with that equation.
 
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