Johnson SR-45 Cooling

[hirschlt37]

Still working on my SR-45…now on the cooling tubes. I’ve seen photos where the top cylinder tubes are aimed towards the rear…not going to the exhaust pipe below the muffler. They looked nice this way…but if I’m correct, the tubes from the top of the cylinders should go to the exhaust pipe….which I believe forces water into the cooling chamber of the muffler? Correct…or did I miss something? Gary, Mi.

[garry-in-michigan]

The lower water outlet aids in circulating water at slower speeds. This is of little concern in racing. Most racers point the outlet where they can easily be seen to warn of an obstructed inlet. (Although unlikely with the rear water pickup Johnson uses.) If the motor has a muffler it is usually modified for racing to reduce back pressure. Tuned exhaust only came into use in outboards after WW2. A megaphone exhaust aids in removing exhaust gases, but also waists gas by pulling some of the incoming charge out the exhaust. . .

Garry in Tampa

[hirschlt37]

Thanks Garry, Sorta what I had heard…but the water circulation at idle was new to me…since I’m not really racing, I’ll go with the conventional hookup. I did add small outlets to the cylinder heads too help with circulation and give me an indication of water flow.

[garry-in-michigan]

It may not cool at an idle with holes in the upper part of the cylinder. That would let air in when the prop wasn’t forcing enough water into the inlet. Add a short length of tubing with a valve to let water out but stop air from going in. This will also show you at what speed the syphoning action kicks in. Let us know how it works out . . . 🙂

[hirschlt37]

I’ll try this…like to get it in the water in June….still work to be done..thanks Gary with the Great Lakes Chapter…

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