how do i check my tach for correct rpm readings, on a 1989 5.7 260hp mercruiser

[BrentW]

hey there guys, i want some advise on how i should/can check and make sure my tach is reading correct rpm. i think it isd right but it seems that i am getting to my engine spec wot when im only about 3/4 into trottle. at idle it seems to be reading possible correct. its sdaying about 600rpm give or take 50 or so rpms maybe and the engine speed to my ear sounds about right. im running a 17p prop which is what manufacture recomends for my 889 sea ray 230 cuddy. but when i get to about 4200rpm which is suppose to be my engines wot im only at about 3/4 trottle and doing maybe 35-37mph i feel i can get some better performance..i do have a brand new 18p 4 blade prop that im thinking about installing tomorrow to see if i notice a difference. but if any one hasd any ideas please chime in and give me some pointers. thanks alot to all, thanks, brent

 

[picklenjim]

Re: how do i check my tach for correct rpm readings, on a 1989 5.7 260hp mercruiser

So have you ever seen how many rpm it will turn at wot? My reference says that motor should turn 44-4800 rpm. 4200 is nothing for a small block chevy. If it goes over 4800 at wot then I would go to a higher pitch prop. Actuall I wouldn't even worry if it went to 5000 rpm. If your really concerned about the accuracy of your tach you can check with one of these.http://www.harborfreight.com/digital-photo-sensor-tachometer-66632.html