More HP from a 115 6 cyl In-Line

[jnewtonsem]

Is it possible to get more power from an 80's 115 In-Line 6? I understand Merc used the same ported block on the 80's 115's as the late 70's 140's. According to Seloc Main Jet on Carb the same @.074 but vent jet is larger on the 115 (.096 vs.090). Can you gain any extra power by changing the jets? If so which ones and what sizes? I also understand trigger is different. What about reeds? Any insight would help. Thanks.

[Raceman]

I'm gonna break one of my rules and talk about something I don't know that much about.......80's model inlines. My experience is with 70's inlines. A little background: In '70 Merc built the first non race, direct charged inline engines, the sixes being rated at 115 and 135 horsepower. The direct charge port configuration represented a significant upgrade from the old crossflow design. These two engines had identical powerheads with the exception of the reed stops and a round plastic air director in the center of the carb throat. The 115 was convertible to the 135 with just these inexpensive pieces, although it did require removal and partial disassembly of the powerhead. (these engines had red cowl stickers) When the 1500's came around in '73, their port timing was different from the 1150's of the same year and they also had a "power port" or "booster port" in the back of the cyl, with a corresponding hole in the piston skirt, a little larger than a quarter, on the intake side of the piston. At this time it wasn't practical to convert an 1150 to a 1500 and I think this difference continued at least through '77. At some point after this a couple of things happened, and I'm not sure exactly when. The 1150 got the hole in the skirt and the big ole power port in the cyl wall. Merc started rating the engines differently, supposedly based on propshaft horespower rather than crankshaft, but gross vs net is probably a better description. Also, in that the 1500's were always a little piston happy (burning right on top of the deflector) and gas had gotten sorrier, and lost the lead, they had dropped the compression by lowering the height of the deflector slightly. I'm unsure exactly the year of this also, but sometime after '77. The point of all this is that if you have an 1150 from the 80's, it is probably very close internally to the 70's 1500 with the exception of the compression. There may or may not have been a modest change in port timing, but certainly not significant. I'm sure there isn't any difference in the reeds, and if there is a difference in the triggers it wouldn't be a performance enhancing change. At least in the '70's Merc had extracted about all there was from the 1500's with any degree of dependability. You should probably live with the 1150 as it is or move up to a V6 which responds much better to modification with it's loop charging and removable cyl. heads.

[jnewtonsem]

Thanks Raceman. Your comments are similiar to what others have said about the differences in the later IL6's. Its my understanding that porting was different in the mid-late 70's between the 115's and the 140/150's. When Merc switched rating HP from the head to the prop (late 70's early 80's) they detuned the 115 to 90 and the 140 to the newer 115. As a result I believe there is very little difference between the 115 of the early 80's and the 140 of the late 70's. I know the new V6's have a lot more ability to squeeze HP, but I have a soft spot for the old IL6's. Combination of an impressionable kid in the 60's and 70's watching Merc's dominate the race and HP circuit, having a V4 Evinrude which spent more time in the shop than on the water, and when I finally got a Merc being able to outrun anything on the river. I kind of like having a simple 20 year old boat that can outrun these big expensive runabouts whose owners don't know what they are doing.

I'm trying to squeeze a little more performance out of it but don't want to fry the engine in the process. Thanks to all for responses.

[stan merck]

one thing your motor has different than a 140 or 150 is the tuner. yours is longer and blends into one outlet. the 140's and 150's had a shorter regular megaphone. lot of work to change but might be worth a couple or one, hundred rpm on top. your porting is identical to a 140 or 150. you just have low dome pistons like the 140. all 150's had high dome pistons. you can try and run more timing for more power,maybe 21 or 23 degrees but you have to run premium and you need to have the eng propped to be able to turn 6000rpm. overpropping kills an inline quick.