JOHNSON F/S 150 TO 175

I HAVE A '93 JOHNSON 150 F/S AND WAS WONDERING<br />WHAT WOULD BE NEEDED TO CONVERT TO 175 HP<br />BORE, STROKE, CARB SIZE SEEM TO BE THE SAME AS A 175. I WAS TOLD THAT BY CHANGING THE AIR BOX, JETS AND MAYBE REEDS COULD ACCOMPLISH THIS TASK.<br /><br />THE SAME PERSON HAS A JOHNSON 225 HO AND HE SAID HE "GROUND" OUT THE EXHAUST PASSAGE IN THE LOWER GEAR CASE AND GAINED 2 MPH. CAN THIS BE DONE ON MY 150 AS WELL ? <br /><br />HE ALSO DRILLED STRAIGHT THROUH THE 2 EXHAUST HOLES JUST BELOW THE ENGINE COVER AND SAID THAT MADE THE MOTOR SOUND MUCH RASPIER. CAN I ALSO DO THIS? <br /><br />THANKS IN ADVANCE JEFF-WI

Re: JOHNSON F/S 150 TO 175

Lets start at the begining. Tell us about your present set up. What boat? What top rpm? What prop? Jackplate? Lets make sure you are using all the available power now before you spend any money.<br /><br />Keep in mind that any potiental gain may be limited by your boats ability to respond to small torque increases. Youre still gonna have the same bore and stroke and the same gear ratio.<br /><br />Tell us more!

Re: JOHNSON F/S 150 TO 175

1998 Stratos 283VR with ’93 150 Jonny faststrike (boat is rated for 175)<br />no feed back Teleflex steering 5.5” set back CMC Hydraulic JP vertical adjustment: prop shaft even with pad to 6” below pad. Motor has approx 70 hours on it since new. Boat was new motor was in a show room display. Bought as a bank repo. Boat and motor run exec. <br /><br />1990 – 92 John GT’s had 175-200 hp till they got caught tampering 93 back to 150 (this may not be exact dates and rating but it’s what I heard).<br /><br />Props: 14.5 x 22 Raker 5600 rpm 58 speedo<br /> 14.5 x 24 Raker 5200 rpm 61 speedo<br />hand held gps wasn’t accurate (by time I get back to dock speed still going up) but test were same conditions for speedo readings.<br /><br />Yes I agree with you that bore, stroke & gear case ratio (1.86:1) r the same but an addition <br />25 hp could yield the following:<br /><br />Not taking into consideration prop slip, pad design, gear ratio and weight of boat for actual speed results I’ll use this as an example:<br />22” Raker at 5500 rpm = 121,000 i.p.m.<br />23” tempest 126,500<br />24” Raker 132,000 8% gain<br />25 tempest 137,000 12% <br /><br />The extra 25 hp and more torque should allow me to run a larger pitch prop at the same rpm and increase speed.<br /><br />If I were to purchase a newer 175 @ x 1,000’s of dollars I think it would enhance my need for speed (if I had da money I’d buy a Alley, Bullet, gambler or stroker With the 250/280 conversion and go 100 but I have to stay on the porch for now).<br /><br />By the way I was beaten by a 28’ Playcraft Power Toon pontoon boat last week, at first I cried but now it’s a funny story to tell. He had twin 250 modified hpdi yami’s on it. Went about 75 mph. <br /><br />My question is if the 175 has the same cowling, gear case, powerhead, etc. what makes up the 25 hp dif ? And also if you know how did the 90 ish 150 have 175-200 hp ?<br /><br />p.s did ya think about the exhaust porting and the straight pipe idea <br /><br />thanks Jeff braaaaaaaaaaaaaaaaap