Determining X Factor Adjustments

[MGuckin]

I have a 1976 18' Starcraft Chieftain with an 84 Evinrude 150, 19" prop, T&T, no jackplate, has doelfin. Plate is even with the bottom of the hull. OEM says 4500-5500 rec. op. range.<br />I rescently discovered that my throttle was binding and butterflies were not opening fully. Repaired that. My max rpm was about 4900-5100 before this repair. Now I can achieve about 5400. In theory, a 21" or 23" prop should bring it into what I thought was a good range at WOT.<br />From what I understand, I should adjust the x factor first to achieve about 5800. I believe this means basically the vertical height on the transom. Increasing the x factor should increase rpms then bring in back down with prop????<br />How do I know how high I can go? <br />How can I do this without a jackplate? Hit or miss?<br />I know I can shim the motor but how high? <br />My boat does squat fairly far when not moving. Light boat with heavy motor. No it is not overpowered.<br />Thoughts??<br />

 

[Hooty]

Re: Determining X Factor Adjustments

Howdy MG,<br />The only way I know iz the ole timey way. Ya use those things call speed or rev sticks. There pieces of wood cut so they fit between the top of your engine clamp and the transom. Shims. I'd start raising the engine 1/2" at a time until it cavitates with that particular prop. Drop it back down 1/4" and see what happens. Probably do this with the engine trimmed in the middle hole and what you would call an average load on board. Of course, when you change props. you'll probably have to change the X dim. again. That's why jack plates are so popular. Keep us posted.<br /><br />g'luck & c/6<br /><br />Hooty

 

[Dhadley]

Re: Determining X Factor Adjustments

You have 4 holes for the motor mounting bolts. Use those to raise your motor so you dont have to worry about putting anything between the top of the transom and the motor.<br /><br />First run your motor as is and make detailed notes. A pen and paper works best. It's amazing what one forgets these days. Note your RPM, speed, holeshot, bow rise, running traits, trim capeabiliy, ect and WATER PRESSURE. Always test with an average load and in your normal water conditions. <br /><br />Now, raise the motor how ever far you like and go for a ride. When you get too high for a given prop you will start to vent either in a turn or on acceleration. Rule of thumb here -- and this is VERY general -- if you can use 100% of your trim range WITHOUT ventalating (slipping) your motor is too low for that particular prop. That equals too much drag and loss of effeciency.<br /><br />Most times you will run out of prop effeciency first. Then you test all over again with your new prop. Watch your water pressure. When it starts to fluxuaite your ready for scoops or something along those lines. Most of the time you dont need to worry about that until you go to a jackplate.<br /><br />Also keep an eye on your steering. Binding or forcing the cable is a no-no.<br /><br />Good luck!

 

[MGuckin]

Re: Determining X Factor Adjustments

Just occurred to me that I had not acknowledged your advise.<br />Thank you.<br />

 

[MGuckin]

Re: Determining X Factor Adjustments

One more question. The bottom holes are obviously below the water line. What do you recommend as a sealer? We are gonna start on this Tuesday. Gonna lift 2 holes to start with.<br />Thanks

 

[Hooty]

Re: Determining X Factor Adjustments

I'd use something temporary at this point like RTV silicone. After ya get the engine where it's gonna stay, go back and drive epoxied dowels in the holes. Push them in 1/16" or so below the surface and then putty over and paint. Keep us briefed.<br /><br />g'luck & c/6<br /><br />Hooty

 

[MGuckin]

Re: Determining X Factor Adjustments

I meant to seal the bolts. I can use the same holes in the hull. The bolts I am concerned about are in an elongated slot about 2" long.

 

[Tracy Coleman]

Re: Determining X Factor Adjustments

MG<br />The sealer/caulk of choice is 3M 5200. Available at your local dealer or Wally World. The only thing between you and a rotten transom is the sealer, don't spare it, upper and lower bolts.<br />Backfire.

 

[MGuckin]

Re: Determining X Factor Adjustments

Thanks

 

[Dhadley]

Re: Determining X Factor Adjustments

Keep in mind that 5200 seals great but is very hard to get off. If you use it make sure the motor is where you want it to stay. We generally use Boatlife caulking. <br /><br />Let us know how you make out. Good luck!

 

[MGuckin]

Re: Determining X Factor Adjustments

I am concerned about permanent seal, not temp. For trial, if it leaks a bit I am not concerned. Only other problem I can forsee is lifting the 389 lb. motor. But I will figure out something. Have a hoist already.