93 200 HP Johnson Ocean Runner Top Speed

[craig-444]

I have a 1993 200 HP Johnson Ocean Runner on the back of a 20' 1990 Four Winns 207 Quest. This is a center console style boat, and reportedly a heavy boat (similary to a Grady White). My speedo only says I am getting about 36 mph all trimmed out at 5800 RPM. I am running a 15 X 17 prop. Everyone tells me I should be near 50 mph. The compression in the top four cylinder is 115, and the bottom two are 110, which is good. I sprayed some cleaner through the high speed jets and those appear OK. The motor appears to run well, however I am not sure what could be limiting my top speed? I know the speedo could be inaccurate, but my experience tells me I am not doing 50 mph.

 

[DJ]

Re: 93 200 HP Johnson Ocean Runner Top Speed

Your RPM seems to be where it needs to be. Your engine is healthy.<br /><br />I would take a GPS speed reading. Otherwise, you're guessing.<br /><br />That may be all you are going to get. The RPM's are the governing factor. You cannot prop "up" because you do not want to turn the engine any slower at WOT.

 

[JB]

Re: 93 200 HP Johnson Ocean Runner Top Speed

Hi, Craig.<br /><br />Estimating your boat at 2500lb on the water, with a semi-vee bottom, clean hull and optimum prop and rigging, I calculate theoretical top speed at about 49mph.<br /><br />You may have a combination of inaccurate speedo (DJ is right, get a GPS reading), poor hull condition and balance, non-optimum rigging, and even tach error.<br /><br />Your indicated rpm at WOT is just about right for an engine putting out full power.

 

[craig-444]

Re: 93 200 HP Johnson Ocean Runner Top Speed

Hi JB and DJ,<br /><br />Thanks for the input...<br />Your are correct I should try and get a more accurate reading before I go to crazy trouble shooting. I did change the tach and rectifier recently, so the possibility does exist that my tach reading is not correctly calibrated. Do you know of a good way to verify my tach accuracy?

 

[Daniel Beckman]

Re: 93 200 HP Johnson Ocean Runner Top Speed

Im shur dhadley can take you to the right answer

 

[Mercathode]

Re: 93 200 HP Johnson Ocean Runner Top Speed

Hi Craig<br />Just for grins, try a different prop along with checking your tach accuracy. May try a 19 inch that should bring your "r's" down to 5500 not that there is anything wrong with the 5800.<br />LW

 

[Mercathode]

Re: 93 200 HP Johnson Ocean Runner Top Speed

Hi Craig<br />Just for grins, try a different prop along with checking your tach accuracy. May try a 19 inch that should bring your "r's" down to 5500 not that there is anything wrong with the 5800.<br />LW

 

[Mercathode]

Re: 93 200 HP Johnson Ocean Runner Top Speed

Hi Craig<br />Just for grins, try a different prop along with checking your tach accuracy. May try a 19 inch that should bring your "r's" down to 5500 not that there is anything wrong with the 5800.<br />LW

 

[Hooty]

Re: 93 200 HP Johnson Ocean Runner Top Speed

Yeah, there's something hokey alright. With those figures and a gear ratio of 1.87, that's almost 30% prop slip. With those same figures, 10% slip would put you at 45mpg.<br /><br />c/6<br />Hooty

 

[craig-444]

Re: 93 200 HP Johnson Ocean Runner Top Speed

I am definately going to try a higher pitched prop...However, I need to find a Dealer that will let me try a few test props before making a purchase.<br /><br />Does anyone think that the previous owner may have somehow changed the gear ratio in the lower unit? If so could I use a strobe light to verify the prop RPM and see what my resulting gear ratio is.