I have a buddy with twin 575's and one of them had a rear bearing failure last year. He replaced them with blowers from The Blower Shop. He doesn't run WOT much but has noticed a decrese in speed. Boat has run the best of 79mph but yesterday it would only run 75 @ 5200. All gauges looked good. Boost was steady @ 5 psi. No other changes have been made since the blower change.

Was there a drastic change in ambient air temp & humidity? How many hrs on the new blowers?? Is the fuel load & boat weight / persons still about the same as the last faster run?? Just curious.. Jamie / lakeside

air temp

Shah Mat,
I'm off 3/4 MPH from my spring #s too. 95 degrees and 90% humidity will do that...........
A question about those blowers. Do they have teflon tipped rotors, or are they machine fitted like the Weiand? If they are tefloned, the teflon strips may need replacement.
When I had TBS rebuild my Merc/Weiand 256, they asked me if I want the rotors tefloned (they aren't from the factory). It would have given me another lb. or 2 of boost at the same rpm, but I declined, because of this annual maintenance.
I have run both styles, and I prefer non tefloned, even though it is slightly less efficient, because you end the season with the boost you started with, unless you FU the blower, of course ...................
Steve

Mine have been all over the place
this year too.

I'm with Customryder on this one.