5.8. Tach setting? 8c 4p or 5p

[Burns363R]

Can someone tell me what setting Volvo wants there tach set to? When i got the boat it was set on 5p, but it has a 8c 4p setting as well. The tach may be reading low, im not sure, WOT was only 3800 ish rpm. 600 or so down from what its supposed to be. So im wondering if its to much prop, or if the tach is off.

 

[bruceb58]

8 cylinder 4 stroke is what it should be set too. To verify the boat tach, try a shop tach and compare.

 

[Burns363R]

is that 8c 4p then? I wonder what the 5p setting its currently on means.

 

[bruceb58]

5P is the number of pulses from a stator if you had an outboard.

For every revolution on an 8 cylinder 4 stroke engine you will get 4 pulses. That is what the 4P means.

 

[GA_Boater]

I'm assuming that there are other settings as well. This is quite common for a universal tach that works for both IO and OBs. The settings with "C" are for the number of cylinders for an auto/truck based engine. Those with "P" are for the number of stator cores in an outboard charging system.

8C 4P is for an 8 cylinder IO with 4 coil firings per rev and 4 stator pulses per OB rev. Keeping it simple I hope - All a tach does is count pulses on the sense input and the setting controls the counting circuitry so "X" number of pulses = one revolution resulting in the correct needle movement. So 5P is for a 5 pole OB stator.

EDIT - I took too long to compose this. What Bruce said. :smile:

 

[Burns363R]

Makes sense I will switch it. Might have somthing to do with when i was at WOT and only showing 3800 rpm. Should have been closer to 4400.

 

[bruceb58]

If you had it on 5P and were measuring 3800, that would be equivalent of 4750.