Re: Johnson V4 85hp To 140hp
The powerheads are completely different. The intake and exhaust ports on the 140 are HUGE compared to those on the 85. You would have to completly disassemble the 85, have it machined, etc. to match the 140 specs and then you'd have it as a 140. If you're going to go that far, you might as well just rebuild the 140.
The exhaust tuner is part of the whole exhaust manifold. If you look at the 85hp, between the cylinder banks, you'll see that it is flat. The 140 in the same area, is bulged outwards. It's often referred to as the bubble back. It helps in the breathing of the motor. The bigger carbs feeding more fuel make more exhaust. That exhaust has to get out somehow, and the tuner helps scavenge that.
More often than not, unless you REALLY know what you're doing and are willing to read plugs, incrementally change jets, read plugs again, change jets again, etc. in order to get the motor to really run right, simply bolting parts on will probably result in poorer performance, more fuel usage, and decreased engine life.
- Scott
