how to prop

[showman62]

89 sportfire 18' im only hitting 45 with a 17 pitch 4 blade and only reving out at 2500. anyone know what way i should go and why im not getting the revs out of it.

 

[bigsbetter]

Somethings wrong here. You can't go 45mph spinning a 17 pitch prop at 2500rpm. We need more accurate imfo. Either your speedo is off or your tach is off.

 

[justincase]

something is wrong! im spinning a 3 blade 21p at 5500 rpm 55 mph

 

[showman62]

maybe the tach is wrong but thats all it showing is 2500 and the speedo is right i used a gps and it matched up. this is a starfire i screwed up and said sportfire.

 

[illMATTic]

what engine are we running?

 

[showman62]

89 starfire stock 350 260 hp. is there a special dimension in od of a prop and pitch or are they all the same od. if i have to big of a prop in od i wont rev out right? what is the correct prop i should start with?

 

[Mark]

Your tach is off. You can't prop without an accurate RPM readiing. Check the setting on the back of your tach. They can be adjusted for 4, 6, 8 cylinders.

 

[bigsbetter]

After you get your tach set right, I'd say a good start for a prop will be a 21 pitch and about 14.25-14.5" in diameter.