Johnson V8 Setup for questions Dhadley

[MarkV_Deep6]

I think I have read all the responses and setup remarks that have been posted to the board and am really grateful for the insight to this engine.<br /><br /> I have a 92 300 Johnson as a single engine on the back of an 25' WA Hydro Sports. It’s a project boat.<br /><br /> I was impressed this Saturday with the performance of the boat as it setup but the RPM's seemed low as you have described the WOT should get up into the mid 6's in all the posts I've read.<br /><br /> I believe the engine is a 20" (23) shaft but the transom on the boat appears to have been cut down on the boat about 3 inches. The engine is resting as low as it will go on the transom so I have the remainder of the holes to raise the engine. Is there a guide by sight to getting close to where the engine should be mounted in relation to the bottom of the V in the hull? I have limited resources to work on the boat and want to get it as close to the correct height as possible the first time lifting it. <br /><br /> As the engine sits now the small plate just under the cavitation plate is about 1/2 inch above the V bottom. I get plenty of speed 49 MPH at 5400 RPM @WOT, and it cruses at about 38 MPH when @ 4400 RPM<br /><br /><br /> Really don't want to spend a lot of money on an expensive Jackplate for a fishin boat just want to set the engine up closer to where it needs to be.

 

[Dhadley]

Re: Johnson V8 Setup for questions Dhadley

The final height of any given engine on any given hull is mainly determined by what prop you're going to use and the technology built into that prop.<br /><br />What prop are you using?

 

[MarkV_Deep6]

Re: Johnson V8 Setup for questions Dhadley

How did I know you would ask that!! <br />I think it's the standard SS Prop as supplied with the engine, it is fairly old but not mangled at all. Unfortunatly I did not have a chance to look at it this morning before leaving for work to get the numbers off of it. <br />That will have to wait till I am able to get home.

 

[Dhadley]

Re: Johnson V8 Setup for questions Dhadley

Are you able to use the entire trim range?

 

[MarkV_Deep6]

Re: Johnson V8 Setup for questions Dhadley

That's another issue... The Trim was not able to overcome the engine power to trim out. I should have trimed it at slow speeds and then tried, but the thought at the time did not occour to me. (Must have had somthing to do with that Ice cold Becks in my right hand.) However on other engines I've owned in the past, the trim has had minor effect on the RPM's. Course that was a properly set up engine to begin with and not a V8.<br /> I Don't seem to be much help with my answers ..Sorry.

 

[MarkV_Deep6]

Re: Johnson V8 Setup for questions Dhadley

Ok so... Let me show more of my ignorance of propellers. The numbers are not what I expected.<br /><br /> Towards the hub the number is 4497 1<br /> Toward the rear of the prop the number is 4761.<br /><br /> I'm tryin to look it up now as I am used to standard pitch and diameter numbers. I did not see a manufacturer name on the prop.<br /><br />Thanks for trying to decipher all this I know you must get a good laugh from people like me.

 

[Strider]

Re: Johnson V8 Setup for questions Dhadley

Hi Mark,<br />I don't mean to hijack this thread (Dhadley is the one or these issues) but I have the same boat with a 300 and don't get anywhere near the numbers you are getting. I'd like to ask you some questions if you don't mind. E-mail me at ken.moors@gte.net. I'm in Charlottesville.<br /><br />Thanks.

 

[Dhadley]

Re: Johnson V8 Setup for questions Dhadley

Those numbers are probably rebuild numbers. The pitch is usually cast in on the hub under the aft washer or on the hub in the forward part of the prop. At any rate if it has been rebuilt it may not be what's cast in anyway. I'm guessing it's probably in the 17" pitch range.<br /><br />As for the trim range, the rpm may come up some while trimming but I'm more concerned if you can trim it to the top of the trim range (not into the tilt range) and the prop not start venting. If you can use 100% of the trim range with the prop not letting go, it indicates you can raise the motor on the transom.

 

[Dhadley]

Re: Johnson V8 Setup for questions Dhadley

Strider, what prop do you run? Is your 300 an OMC V8?

 

[MarkV_Deep6]

Re: Johnson V8 Setup for questions Dhadley

Good another person with a similar setup. I thought I read a past post with a similar setup. The numbers I was getting for the first outing on the boat were off a new OMC tach, and the speed was from a Raytheon speed monitor that seems to be close, if not spot on. Please let us know all the spec's etc. with your setup and we can try to make an educated guess for correct setup with the boat.<br /> Thanks Dhadley for the prop analysis. I have spoken with a prop sales agent that suggested I call the manufacuturer to get the best suggested prop configuration for the size boat. <br /><br />The trim is probably not going to work properly to help in determining the correct height. It does ok for lifting the engine as long as it is not bumping against the power of the engine. Its a long story but I had to replace the T&T. The unit I replaced it with was from a smaller engine and believe this is the reason it's weak.<br /> I made several sharp turns with the boat to get a feel for handling charistics and did not notice any cavitation at all. <br /> I was hopeful a sighting of the engine position in general had been noticed as a guide prior to raising the engine. <br /> As you have pointed out this is probably not possible with all the variations that come into play. Perhaps the best method would be just to raise it a slot at a time to get the best operational setup. Renting the lifting gear more than once was something I wanted to avoid, as well as the work involved. (I'd rather be on the water)

 

[MarkV_Deep6]

Re: Johnson V8 Setup for questions Dhadley

Strider Hmmmm that was the name of a 24' straight inboard I rebuilt in the Bahamas. Loved that boat!<br /><br />FYI My name is Ben... the MarkIV_Deep6 is a handle representing my first carreer.

 

[Dhadley]

Re: Johnson V8 Setup for questions Dhadley

Do you know anybody with a prop for an OMC that you could try? Something in the 15 or 17" range. Doesn't matter what brand just something that we know what the pitch is to get a baseline.

 

[Strider]

Re: Johnson V8 Setup for questions Dhadley

Hi guys,<br /><br />Here's my setup. The boat is a 1990 Hydra sports 25' W.A. Vector series with the hard top. 20+- degrees deadrise. Motor is a Johnson V-8 300 HP. I've got 27 inches from the cutout to the bottom of the V in the hull. The Cav plate is 3/4 inch above the V and I can get it to cavitate if I trim it up too far. The prop I'm using is a Power Tech Offshore 3 blade 15 1/4 inch dia and 17 inch pitch with cup. <br /><br />I had a Johnson mechanic go through the motor last year and he ran it on a test prop, compression, fuel flow pressure, rpm's etc., and said it was in fine shape. <br /><br />The thing that has me scratching my head is this: I get about 25 to 27 mph at 4800 to 5000 rpm and 38 mph at 6000 rpm. W.O.T. is 6200 rpm and 39 mph or so. I tuna fish and the boat is loaded with several hundered pounds of Ice and crap (I mean important fishing gear) when I go out but even coming home with only 75 gals of fuel on board I've never seen speeds like Ben is getting. <br /><br />Have you ever weighed you boat Ben? I don't know what mine weighs but it sure feels heavy on the ramp.

 

[MarkV_Deep6]

Re: Johnson V8 Setup for questions Dhadley

Well measurement show its 15 inchs in diameter but the pitch will not be easy to find. I don't have a loaner prop to install so that’s something that will need to be done. Do you have a guess at the correct pitch?<br /> I see strider's pitch for his engine that is turning about the right RPM. 17 so I would guess that’s a good a place as any to start.<br /> Using the measurements to check with mine indicates we have the same transom and cut down. Checking the cavitation plate seems to right at 3/4 of an inch above the bottom of the v... Same as yours. Do you normally trim out the engine to gain rpm and how much? Since our engines are mounted the same I would assume mine would cavitate also if the trim was doing what it's supposed to. Is you engine resting on the horizontal pin or on the hydraulic pins of the T&T?<br /> I believe your rig is going to be a bit heavier than mine. I do not have the hard top. It's an 86 WA, don't know if it a vector or what they called it, It’s really heavy. I had just a little over a 1/4 tank of gas when running in a slight chop. The boat had myself my wife and son, and a cooler full of cold beverages. The fishing crap..I mean equipment, will have to come latter but that should only add a couple hundred pounds at the most. It would not seem that you we would have such a disparity in speed and RPM. I think I saw in your previous post that the gas supply was gone over to ensure good fuel delivery. It’s a mystery to me… doesn’t seem like everything is correct with you engine or something. I assume you have trim tabs on the boat?<br /> The only person I have to work on my stuff usually is me cause I a (cheap @^%$%*@) according to my wife.<br /> I need to decarbonize the engine, I doubt that has been done for a while if ever, and I’m getting all the parts to convert it back to VRO Pumps. That’s a challenge with all the wires the previous owner changed, spliced and left cut.

 

[Strider]

Re: Johnson V8 Setup for questions Dhadley

I run my motor at about 1/2 trimed up I would guess. If I trim up too much the rpm starts to climb but speed starts to drop and I can hear it start to grab air. My motor is resting on the trim and tilt arms and I have trim tabs but barely use them. Mostly use the trim tabs to balance it port to stbd.