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Author Topic:   Correct Prop without a Tach
bones posted 08-28-2008 06:23 PM ET (US)   Profile for bones   Send Email to bones  
Does anyone know how to determine correct prop size/pitch without using a tach? I have a 1966 13-Sport (the hull may weigh 350-400 lbs loaded) with a 2004 4-Stroke Merc 30. Top end is 30-31 mph (GPS - no real current). Does this sound about right? Is there any way to tell if my engine is R-ing up too much, or not enough?

Thanks

Tohsgib posted 08-28-2008 09:27 PM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
Sounds right but just keep it under WOT for any period of time. Not saying you can't mash it down but if unsure(which you should be OK) and even if you are sure...you should never run for extended periods at WOT. There is a rev limiter that will be a couple hundred above redline to save th engine. There is no reason to run WFO when you can run 7/8 and get 95% of the performance and save the engine and fuel. In reality...3/4 throttle is ideal for engine preservation and optimum fuel economy. Running an engine WFO will starve it of 85%+ of its usefull life. Running at 75% will give it 100%. So..running at idle or 75% will yield the same results long term.

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