Re: Can you rejet a Force 125 hp to get more power out of the Carbs?
A Question and some OT fun...<br /><br />I am curious Mr Merc..<br /><br />Do they do it on purpose? make the same block for 2 different HP motors, and then detune one to a less efficient exhaust and smaller carbs so they can sell it without having to produce a new block for the lower hp motor? or is it a case of hotting up the current block to sell it as a higher HP unit?<br /><br />I have an old Johnson 100HP in excellent nick, and I was toying with trying to up the HP so that it is a 100 at the prop instead of just the flywheel, get a tiny bit shaved off the heads, maybe a port and polish.. and perhaps pick up an old 115 out of the paper (they go very cheap for wrecking around here. (I have seen less then 100 dollars in some cases.) and change over the exhaust... I don't want a huge power increase, just want a "real" 100 HP.. give me a mile or two of extra speed and maybe even inprove the engines efficiency (the port and polish and port matching).<br /><br />Since I am capable of doing all the work myself, (cept the port work, and I have a friend for that)and I already have a spare powerhead for it,, all I really need is the bigger exhaust.. <br /><br />My question is, do I need to change the exhaust just to get a paltry 5-10HP extra? surely port matching, minor increase in compression, (maybe up to 110psi from the 105 they are now.) and other minor improvments would get me that?<br /><br />Dont' get me wrong, i'm doing this is mostly for my curiosity's sake, I have been rebuilding engines since I was 12, (started with a lawn mower and moved up from there.) and I was the type to put big engines in small cars as a teenage, just cos we could. (and they went really fast
<br /><br />Incidently, in the interest of playing around here, has anyone ever considered adapting the fuel injection kits you can buy to add to 4 barrel car carbs, (like holleys) to an outboard? the idea intrigues me,, you would have to up the injector size to compensate for premix (then again maybe not cos most of them were designed for 5.x litre V8's anyway), but it should be entirely possible, I wonder if the result would be the same as it is in Cars, bit less fuel, better throttle response (holeshot) and maybe a couple of extra hp up top... The only real problem I could forsee would be those introduced by the outboard having side draft carbs instead of tops..<br /><br />I was also thinking of buying one of the water injectionn kits for cars and adapting that to fit, so on return each trip, and quick water decarb 20 minutes from the boat ramp would clean things up with no real effort on my part..<br /><br />I might try these ideas..., I wish I had access to a dyno so I could test before and after...<br /><br />And I am a real lover of old engines.. so easy to work on, so I like to get everything I can from them... as a sort of twisted hobby.<br /><br />Oh well, its fun to think about..<br /><br />I even toyed with the idea of tossing my powerhead and machining some adaptor plates and stuff so I could bolt a 13b rotary engine to the leg, but that gets complicated due to the direction of rotation and stuff. building something unique is always a big attraction to me, even if it costs more then something off the shelf..<br /><br />anyways, have a good night.. (its 4.30am in the morning here, so I'm off to bed.)<br /><br />regards<br /><br />Franki
