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Which holes in the adapter plate get blocked for drystacking?
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Look for the small (about 1/8") hole to the aft of the exhaust pipe... highlighted below. RTV or similar...no need to overdo globs of it and make sure you don't disrupt where the gaskets rest on the plate.
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Thanks for the info, any other exhuast/cooling mods? Run thermostat or no?Comment
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Don't run the thermostat. Initially it will prevent water flow to the exhaust side of the piston until it opens which is tolerable on a service engine but that is when the race motor is being most abused as it is at max effort trying to plane off with a cold motor. Leaving it in won't kill the motor but why not make its life easier.Comment
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I just ordered the j/a gearcase and noticed on racing outboard website, they sell 1:1 gear sets. What conditions would they be better than 14:19?Comment
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I think that for all-'round running, you'd be better off with the reduction gear ratio because it'll give you better selection among props.
Historically, the Merc Quicksilver ratio was 1:1, primarily to get the prop speed up with the then ''new'' surfacing-style propeller. Then Champion introduced the 19:14 reduction ratio gearbox and began beating the pants off Merc 1:1s in 1955-56 because of better ability with bigger props coming out of the corners. The Champion ratio was more nearly like the old pre-war (WW2) ratios of the OMC alky engines, but Champion coupled the older ratio with the new ''surfacing prop'' technology.
Merc countered in 1959-60 with their new 21:16 reduction gears in their ''Conversion'' kits to put Champion temporarily out of competition. The Merc 21:16 reduction was a slightly less reduction than the Champion 19:14 reduction (5 teeth difference on each manufacturer's set of lower-unit gears). But the Champion reduction (same as the current reduction for Merc-OMC J and AX engines) is probably better overall.
If you look at current alky-unit reductions, you'll find much bigger reduction ratios, which enable the powerheads to rev much higher for more peak horsepower (14,000-16,000 RPM) while maintaining prop speeds that are more nearly optimal.
To answer your original question, the 1:1 gears would be best only for straightaway time trials, even if then.Last edited by dwhitford; 10-02-2017, 07:29 PM.
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