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I have been given a couple of ways to figure horsepower. I was wondering if anyone knows which way is correct, or knows of another way to do it. 
 
I have a IV-P with a TSIO-550. I cruise at 28" 2500rpm- 17.5gph which I beleived to be 65% power. Another IV-P owner sent me a power setting chart that shows 28" 2400rpm- 15.5gph as 65% power. 
 
I have been told that using 13.8 x fuel flow would give HP 
13.8x17.5= 241.5hp 69%    14.7x17.5= 257.25hp 74% 
 
I have also been told that using 14.7x fuel flow is the way to 65% power. 
13.8x15.5= 214hp   61%     14.7x15.5= 228hp  65% 
 
Are there any members that can shed some light. In have GAMI, and want to run at 65% power LOP.  
 
I now set my settings at 28" 2500rpm, then lean to 50 LOP which gives me 17.5gph. 
 
Any input appreciated. 
 
Mark 
N37MB 
 
 
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