Reaching WOT, but not reaching even close to top speed :-(

[vickerslane]

Orginally I had a problem with my boat not reaching WOT or top speed. I was only getting about 3,700 RPM and 25 MPH, but now I am getting almost 5,000 RPM but still only doing about 27 MPH. I will tell you that the issue with my RPMs was that my spark plugs were not gaped properly (changed them out), My sparks cables were corrodied (changed them), and my distribitor and coil needed to be replaced. I found that I was having a lot of electrical issues. I even had to replace my fuse box because it was not getting a good connection in the fuses.

I had high compression in my cyclinders and we found that my head gaskets had not only gone bad but were the wrong ones! We replaced them and painted all the covers.

I took the boat out for the first time yesterday after all these issues were fixed and I was hitting about 5,000RPMs but still only doing about 27MPH. I only have a 17 pitch prop but I wanted a good hole shot to pull skiers and wakeskaters out of the water. I feel a little more power than I had but not what an extra 1,200RPMs should feel like.

I will say I had 4 guys on the boat and my engine is a 3.0 4 cyclinder mercruiser but I feel I should still be getting more out of my 1998 Sea Ray 180. Any advice?????

 

[greg82255]

Re: Reaching WOT, but not reaching even close to top speed :-(

5000 rpm with your drive and a 17p prop does not give you 27mph. You might want to change out that tach and see if you are actually getting 5000 rpm.

 

[Aatcman]

Re: Reaching WOT, but not reaching even close to top speed :-(

Four possibilities....

1. Your tach is lying.. Test with another tach (Check the cyl selector on the back -- make sure it's set for 4 cyl)

2. You need a taller (high numbered) prop... (I had a 19 on my 2.5 and it gave me 35mph at 4100 RPM, 4400 rpm WOT in my 18' runnabout)

3. Your engine coupler is spun (do you smell burning rubber -- like a burnt vacuum cleaner belt?)

4. Your prob hub is spun..

Your WOT for the 3.0 should be between 4400 and 4800. 5000 might be pushing it....

Hope this helps...

 

[Aatcman]

Re: Reaching WOT, but not reaching even close to top speed :-(

Remember it's only a 4 cyl -- it's not going to jump out of the hole and smoke the 454 sitting next to you....

Higher pitch prop = higher top speed, but less torque (which means you'll go faster, but it'll take longer to get to top speed)
Lower pitched prop = slower top speed, but more torque (which means you'll get to top speed faster)

 

[vickerslane]

Re: Reaching WOT, but not reaching even close to top speed :-(

It is doing 4,800 RPMs. The tach is right because I have a GPS and it says the same thing...27 MPH.

I know the lower the pitch, the higher the torque but it doesnt even seem like it is pulling people out the water like it should. I want to put a 19 pitch on there but im afraid it will bogg down the boat at the start.

Is there a performance Carb out there that could help me out? This is getting frustrating. And to top it off I still can't get the stiff steering fixed. I think I just need to replace the steering cable. Any advice on where to get that inexpensive?

Thank everyone for the help!

 

[tschmidty]

Re: Reaching WOT, but not reaching even close to top speed :-(

GPS says 27, doesn't mean your tach is right, but let's presume it is.

What kind of shape is the prop in? Captivation plate?

Is the prop hub spun? Mark it and do a run, are the marks in the same spot? Engine coupler is not as easy to test, but I would reckon you would hear or smell something if that was unhappy.

A 19p prop should be a good match between top speed and hole shot for you, you have something else besides just a pitch issue.

You don't need a carb. Steering most likely needs a new cable, but disconnect it and move the drive and wheel to make sure they turn freely. I think you have a new enough hub (teleflex most likely) that you can just replace the cable, otherwise you need the hub and cable.

 

[vickerslane]

Re: Reaching WOT, but not reaching even close to top speed :-(

Sorry, I was confusing Tach for speedometer for a second. I will check the Tach but I am sure it is good. It was reading 3700RPMs before I did all the electrical and engine work. It seems like the engine is running a lot smoother.

How do I check the Hub?

 

[Al Bee]

Re: Reaching WOT, but not reaching even close to top speed :-(

I have a 2008 3.0, and a 19P 3blade aluminum gives a top speed of about 40mph and a WOT RPM of 4500. Hole shot is decent as well. With a load of four adults, three 10 year olds, a boat load of gear, and I mean a boatload, pulling a 6ft, 200lb NEWBIE out of the water on a wakeboard, is no problem, generally out before the prop wash. I have found that the only time it struggles, is when I have a very demanding weight at the rear of the boat.

 

[vickerslane]

Re: Reaching WOT, but not reaching even close to top speed :-(

Now the boat is back to 3700 RPMs. My batteries keep dying too. I am going to check the alternator. Could a bad alternator have anything to do with lack of RPMs and speed????