turning my 70;s 115 jonhson into a 140

[ShiftyOne]

In my manual these to motors are nearly the same the only difference is bore: 115 is 4.380 and the 140 is 4.500. timimg: 115 is 26 degrees and the 140 is 22 degrees and everything else is the same so my guess is that the carbs and intake would have to be swapped.<br /><br />Not sure if anyone would have this info but I'm looking for the bore of a 115 carb compared to a 140!

 

[Droll]

Re: turning my 70;s 115 jonhson into a 140

Try the search .<br />Search Words: = "Increas Horsepower" or "v4 power"<br />Member Number or Public Display Name: = Dhadley ( OMC performance guru-Dhadley )<br /><br />This topic has been use many times <br /><br /> Example post <br /> Example 2

 

[ledgefinder]

Re: turning my 70;s 115 jonhson into a 140

If you have a 4.38" bore 115, it's 1969-70. You've already got the same size carbs as the 140. The 1969-70 115s came with 1-5/16 inch carbs, and I think most of the 135/140s also came with 1-5/16 (some had 1=3/8).<br /><br />Your motor's different from the 1973-77 V4s, and not much interchanges with them. The 1969-70 115 was the hottest motor OMC made at that time, and frankly I think it's got just about the right powerband. They goosed it a bit more with the 1971-72 125s - still flatbacks and an insignificant bit more displacement. If the motor's not doing what you need on the boat, make sure it's running right (check compression, etc.), propped correctly, and as high on the transom as it'll go. You can see the old posts for further discussion.<br /><br />You can get more from it by milling the heads, squaring/raising the ports, relieving the exhaust, etc. but every bit of it moves you closer to melting a piston top.

 

[R.Johnson]

Re: turning my 70;s 115 jonhson into a 140

Dhadley has had some real good posts on tweaking these older motors. I have a 1972, 125 that I run on a 15.5 ft Checkmate, and two 1973, 135's that I am building as time and money allow's. You can have a lot of fun with these old motor's, but I sure whould not want to pay someone to do the work.

 

[fast_c_class]

Re: turning my 70;s 115 jonhson into a 140

shifty,<br />I recently did the conversion myself and I must say I only gained 5mph from it, and the idle definitly isnt as smooth. This is also on a 14ft hydrostream that is EXTREMELY LIGHT, on a heavier boat you may hurt your holeshot.<br /><br />If you must know.<br />The parts that are different on a 140 consist of:<br />bigger carbs, either 1-5/8 or 1-3/8<br /><br />A better head with a different squish pattern<br /><br />the exhaust "bubble" and the stuffers that direct the exhaust into the bubble.<br />You can leave the stuffers out but you will loose some power down low and gain some up top, not good if you have a heavy boat (over 1200 lbs)<br />Also, you cant put the stuffers on without taking the block off and taking it to a machine shop. There is also a small slot that needs to be machined at the bottom of the block for better exhaust flow.<br /><br />If you want more out of it, you can cut the exhaust tuner down, square off the ports, clean up the intake tract (get rid of the casting parting lines)and add some plastic reeds.<br /><br />As you can see its alot of work and took me about 20 hrs to complete the conversion. looking back id go and buy a 1985 newer 115 (basically a detuned 140) and put the old heads on that or buy a v4 looper.<br /><br />If you do decide to go through with the conversion id suggest searching the forums on www.screamandfly.com , there is alot of info on that sight on doing the conversion.

 

[ShiftyOne]

Re: turning my 70;s 115 jonhson into a 140

i might have the bore wrong but it is a 1973 johnson 115 what is the best running rpm 5500? or around 6000?

 

[fast_c_class]

Re: turning my 70;s 115 jonhson into a 140

i think running by yourself you should be around 5700rpm, that way when you load the boat down with more gear and peaple you wont be lugging the engine.

 

[ShiftyOne]

Re: turning my 70;s 115 jonhson into a 140

Ok I don't really want to do any porting because this motor is on a 17' glass bowrider and i travel 30 miles up the lake often. just trying to gain some new power. I run a decent 35 mph on gps right now!