1986 268 weekender engine speed and planning?

I think you missed what the guys are trying to say. Will your boat plane at all without using the tabs? If so, do you normally use your drive trim, and if so, how much?

On my 260, I have to get on plane, and then trim the drive for the best performance. Only then do I even think about hitting the tabs. Try getting on plane without tabs, and then give your drive a small amount of "up" trim. Wait for a change in RPMs. If you get no change, try a little more up and wait again. Mine requires only a slight bit of up. When you get the "up" trim right, you will see your RPMs increase a little, at which point you can back off on the throttle a bit. If your RPMs start to drop, you went too far up, use down in small increments to get back to the best trim you can. See what speed/RPM you get trying this and let us know.

I suspect that once you get this part correct, you will find that you need very little tab to keep the bow down.

Michael
 
I thought i did answe that question.. Yes the boat planes without trim tabs. once on plane i do trim up on the drive some.My main concern was the fact that if i'm doing 4000 rpm's the boat is going 28 to 34 mph according to gps and water condition. Once i trim the drive up some and the r's increase slightly i try to back her down to 3500 rpm's the boat starts a slow steady decrease in speed.If i keep the rpm's around 3500 my speed will stay at 11 to 13 mph. Just thought it should be higher high teens low 20's. The boat takes full throttle to get up on plane which is to be expected with a single engine heavy stern boat
 
lime you could be right about that. you might just have that much load to keep up on plane. you have a lot more boat to push than mine and i wouldnt be happy with any less power than i have now
if the bottom falls out that fast and your motor isnt tired and your prop hub isnt spun and your trim and trim tabs are working properly and your boat isnt waterloged and your boats bottom is clean that dos'nt leave much else i can think of that can be wrong.
the only thing that hasent been mentioned is a compression check and a tune up(dont rember seeing that anyway)
may be someone can come up with more ideas.
 
when we got the boat last year it had a blown engine. I rebuilt the engine last year along with a complete tuneup. Also replaced the upper drive unit with a new one. The boat doesn't appear to be water logged. It sits well in the water and i drilled some test holes in the transom and it wasn't wet.I'm seriously thinking og either building another 5.7 and gear it more for torque or installing a big block
 
That's a big drop-off in speed from 4000 to 3500 rpms. Two things come to mind. With the drive trimmed up some, as you begin to slow the bow may start coming down and the outdrive may start coming up. Then it may be loosing efficiency.
But I'm still thinking it's the prop. That top speed even sounds a little high, so you may have a prop with lots of pitch but not much surface. So, once it gets going and you are fully on plane, and at full speed you are really moving. But at lower rpm you don't have enough surface to give the push you need. Can you confirm the prop.
 
lime4x4 said:
trim tabs are working. When we got the boat i installed the bennett trim tab indicators
Click to expand...

I was thinking about doing that myself. What all is involved? My old switch is getting worn out and I like the indicator idea.

If "everything" seems optimum (rebuilt motor, clean bottom, correct prop, functional tabs, correct trim, etc) but rpms fall off then could the throttle itself be sliding back? Did you rebuild the motor to stock? Maybe after the break in period it will perform to expectations?
 
the prop is a michagan wheel 3 blade alum

For the trim tab indicators it was bad to install just replace the tops of the current bennett trim tabs,drill another hole in the transom for the wire. Then fish the wires where ever the indicator is located. Took me about 1.5 hrs to install
 
Also the engine is broken in. 50 hrs on it last year and 15 hours on it so far this year
 
okay i was able to play with the boat tonight. Once on plane and drive trimmed out i eased the throttle back down to 3500 rpm's. The speed started to drop but not as fast.Once i got down to around 22 mph i trimed the drive up some more. The speed increased to 23.6 and the rpm's went to 3600 rpm's. So i'm making progress.
Plus this time i was able to turn on plane speed dropped to 19 mph and once i striaghten out the speed went back up to 23 mph. All reading are from a gps
I still would like to find a better prop to help get it on plane faster. Right now at full throttle the boat starts to come on plane at 18.7 mph
 
I have a different model (30 weekender 1977) 12' beam, twin 454's and 18 knots by gps is about slow as I can go with out falling off plane but that's at 2,000 rpm. I am belive 18 knots is what it takes to power up the deep vee design.
 
I really like the Merc Mirage Plus prop for this boat. Actually mine is a 1980 260 with a 5.7L and 4bbl. Your 268 is a little different, but not too much. Based on all your info above I would say a 15 in Mirage would do well. Mine will come on plane at 2000-2500, depending on load, and stay on plane at 2000 with zero tabs. The mirage prop has a big surface area and can work a lot of water. You'll see good low end power and significant speed improvement over aluminum. I generally cruise at 2500-3000 and get more speed than you're getting. You just have to check that you can still turn at least 4200 with the Mirage, but you should be able to.
 
the only one i can find is 1/2 inch bigger in diameter Will that be okay. 15 3/4 X 15 RH SS 3 BL
the cheapest i found is 479.00 bucks
 
That prop will fit. Just make sure you have the proper low-profile zinc anode tab so the prop clears it.
 
I was able to pick up a used mirage prop for 125.00. It helps greatly. If i play with the tabs and trim the outdrive up i can keep her on plane at 3200 rpm's doing 24 mph.
 
my mirage II has vent holes you can open and change to help engine spool up faster and get up on plane faster
you might check and see if yours does. the are black dots that appear on the front root of the blades
 
Sounds like a good deal. Was it the 15in you talked about?
I'm sure you can stay on plane at 3200, but I hope you can stay on plane a lot lower than that. Otherwise, you have a dead area between about 1000 (off plane) and 3200 (on plane). Of course that all depends on your perception of "on plane".

But, I've heard this so many times I wonder if the 268 has an issue that the 260 did not.

And Gary, isn't a 454 over the HP max for the Alpha outdrive?
 
yes it is now. mercuiser did it for 2 or three years. "87" to "89" or so and had to much trouble with them. enter bravo I and a 300 hp rating for the alphas
they did have a 1.32 to 1 and a 1.51 to 1 heavy duty gear sets to go in these units to help them live
thay came painted oyster white and were sold as sea ray drives, not mercuiser
 
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yes it was the 15 3/4 by 15 prop. I'll play some more this weekend and c what happens
 
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