Re: 1971 115 hp lower unit
Let me introduce my self, I am 69 years old, have a degree in Diesel engines and have been around outboard motors since I was 16. I spent 7 years at OMC snowmobile and Marine Engineering and 2 years at Mercury Marine and worked with Dr. Morgan in advance research. I worked on production engines, C-6's and the t-II. Do I know what a Direct Charge engine is? yes I do. I've worked on cross flows, Direct charge, loopers, three port, rotary valve and reed engines. I've worked NA's, and turbo charged gas and Diesel engines. I worked and ran a 33 megawtt Diesel power plant in Bay City MI with four Pielstick Diesel engines. I prop all my DC mercury engines for 6000 with only me in the boat. Do I run them there continuous, no, as you know when loading more weight in to a boat the speed of the engine falls off. I use only high test gas and a oil mix of 24:1 (TCW-III oil). If you go by the old Mercury speed recommendations of 4800 -5200 RPM you will put yourself into a lugging condition very quickly. Sooooo can you run a 1350 all day at 6000 RPM, Yes. Some further info, the only difference between the 1350 and the 72' 1400 was the tuned exhaust in the mid section. The 1500 difference was a boost port located between the two transfer ports and a large hole in the piston skirt. The Exhaust port and trasfer port timing are all the same.
The 1350 is a torque engine due to porting and if the figures you posted are correct you should have picked up almost 5mph! The 1350 is one of the first "Direct Charge" engines as Merc called it and came out on 1970 thru 1972 engines. The difference was a new piston deflector design and milled instead of drilled ports. This feature is on the transfer side of blockalong with the C-shaped piston deflector, shape of the transfer ports and the dividers/splitters in the transfer port covers/channels.
