View Full Version : Tach vs. PerfectPass: RPM Discrepency

07-23-2008, 05:37 PM
So my tach reads 400 or 500 RPM lower than perfect pass at WOT. Who do I believe? The boat is a 1992 prostar 205, has a 13x13 four blade prop, and has the 285 HP 351 ford. The tach reads between 3900 and 4000 RPM, while perfect pass reads 4350 - 4400. The discrepency is not enough to make me believe teh tach is set to 6-cylinder mode. I dont believe theres a trim pot on these things, is there? Any suggestions?

east tx skier
07-23-2008, 05:40 PM
From what I know of WOT on my old boat, I think PP is closer than your tach. My 93 PS 205 ran 4,600 with a three blade. So 4,400 with a four blade sounds about right.

07-24-2008, 08:45 AM
I konw that the tach on my '95 is about 500 RPM slow at 4,000 RPM, according to the Snap-On timing light I was using. I assume the timing light was accurate.

Kingsley X-1
07-24-2008, 01:52 PM
no true answer for ya, but the gauges in my 08 dont exactly look like they are super duper highend quality gauges...IMO