johnson 115 more power needed

[74Baja]

Hi, I have a 1974 johnson 115 on a 1974 16 foot Baja speed boat and was wondering if there is anything that i can do to get more power. i was concidering boyesen power reed valves. do they work and how hard is it to install them? The compression is 110 psi. in all cylinders. i have an 18 pitch stainless steelprop and when i floor it i get about 5200 rpm. thanks for your help.

 

[Dhadley]

Re: johnson 115 more power needed

Good info. Your right, you should be disapointed with the performance. I'll bet the holeshot isnt the greatest either. Those Bajas are great boats and a lot of fun. <br /><br />Lets start with the location of the motor height-wise in relation to the bottom of the boat. If the motor can be raised on the transom, go ahead and raise it. Real easy, virtually free and painless. By reducing gearcase drag we will increase the efficiency thru the whole rpm range using the same prop. <br /><br />You didnt mention if your prop is a 3 or 4 blade. A 4 blade will generally run higher (toward the surface) than a 3 blade. It doesnt really matter which you have so for the moment lets raise the motor and get the rpm's up.<br /><br />Keep us posted. Good luck!

 

[74Baja]

Re: johnson 115 more power needed

thanks Dhadley, v<br />the prop is a 3 blade. i was wondering if you raised the motor on the transom would you be putting alot of stress on the transom because it isnt resting on top? also how would you fill the holes that the bolts left when it was in the old position? you are probably right though. that sounds like it is a great idea, i was hoping i could squeeze a little more juice out of that old engine without spending much. thanks!

 

[Dhadley]

Re: johnson 115 more power needed

You use the same mounting holes in the boat. No need to drill more. You have to support the motor (a hoist is best) remove the top bolts, losen the bottom ones and raise the motor until the other holes in the top line up with the bolts in the boat. The bottom bolts are in a slot.<br /><br />If the transom is sound it'll be fine.

 

[74Baja]

Re: johnson 115 more power needed

thanks so much Dhadley! any more advice?

 

[Dhadley]

Re: johnson 115 more power needed

Sure. Go have fun -- I mean test. <br /><br />John Tiger wrote an article for Bass & Walleye magazine about redoing a boat as a father daughter project. I havent seen it yet but it should be interesting. Heck, anything Tiger does is interesting....<br /><br />Guess what they used? A older small Baja with a V4 Evinrude. For skiing. He told me it runs great. Keep an eye out for the article. It will have some real interesting prop data.

 

[phatmanmike]

Re: johnson 115 more power needed

try lookinhg at some aluminum jackplates. whether they are hyfrolic, manual, or fixed height, you can get"more power" from your setup, and its infinitly adjustable. if you dont like the way it acts, just move it up or down an inch, but one thing is certain, you WILL increase performance.<br /><br />DHADLEY is the daddy of this kinda stuff, not to mention he is the king of V4 knowledge. good stuff.<br /><br />the boyesn reads should be about a 2or3 on a scale of 10, difficulty ratings. depends how much work your willing ta do yerself. your motor is an older on , so you dont have as much"stuff" that has to be taken off to get that intake manifold off your motor. if it were me, i would do the jack plate AND the reeds, and while the reeds are off, id spray a bunch of DEEP CREEP in the crankcase. but im not a pro, im just me. <br /><br />mike

 

[74Baja]

Re: johnson 115 more power needed

hi i was just wondering how i can tell how far the motor can go up on the transom. thanks for the info.

 

[phatmanmike]

Re: johnson 115 more power needed

you can safely raise the motor untill the top motor mount bolts are about 1 from the top, when you run out of room for the top bolts, you need a jackplate

 

[74Baja]

Re: johnson 115 more power needed

then is it possible to lift it too high and get cavitation with the prop or will it come out of the water when you trim up? also will it be so hi that the prop wont be under the boat but behind it or to high in relation to the bottem of the boat?(sorry, im not an expert)

 

[phatmanmike]

Re: johnson 115 more power needed

oh yes, absolutely! that is where the jack plate comes in play. if the motor is flat against the transom, and the prop is too high, you will cavitate. definately.<br /><br />with the jack plate, you not only can raise the motor higher removing more of the lower unit out of the water, but you move the motor back 4, 6, even 12 inches or more depending on type of plate used. by moving the prop/motor back, which is called the "setback", you give the prop some "cleaner" water to run in, allowing more bite and grip, this improving effiency. thus giving you more speed with the same hp, also giving you more fuel milage too.<br /><br />you can get a fixed height jack plate(non adjustable) for under 100 dollars at any westmarine.com or boatus.com<br /><br />if you need to adjust the height, you just loosen the mount bolts, slide motor up or down, and tighten bolts

 

[74Baja]

Re: johnson 115 more power needed

thank you so much guys! do you know about how many mph i will gain?

 

[phatmanmike]

Re: johnson 115 more power needed

usually i see people add a good 5 0r 6 mph with a nice setback and lift, but of course, every boat is different.<br /><br />heres a nother sugestion.... check ou this post by another iboats forrum user, wallyehead. that made his own jackplate...<br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=007238#000000

 

[Dhadley]

Re: johnson 115 more power needed

How high you can run the motor depends largely on the technology built into your prop. Obviously a $700 Mazco should run higher than a $200 general purpose prop.<br /><br />Yes, if we could hide the gearcase behind the transom (no drag) and still have the prop "bite", that would be fantastic. Thats the whole reason for the success of the surface drives like Areneson and the old Kamma drives.

 

[Solittle]

Re: johnson 115 more power needed

Best to have a water pressure guage and temp guage and monitor as you experamint. You can raise/set back the motor too far and not get enough water for cooling.

 

[74Baja]

Re: johnson 115 more power needed

is it possible to hide the gearcase and still get prop bite?

 

[Dhadley]

Re: johnson 115 more power needed

You can hide a lot of it. On V bottom raceboats its not unusual to have the centerline of the propshaft above the pad (bottom).

 

[Marc J.]

Re: johnson 115 more power needed

Hey 74Baja, drop me a line at my e-mail address (it's on my profile). I have a similar boat and would be interested to know more about yours. Not trying to hi-jack your thread, just hoping to get your attention.

 

[Marc J.]

Re: johnson 115 more power needed

^^