Need Volvo Prop Help 292 Fastech With Twin Volvos and 5.7gxi Catalysts

[hotstang461]

So I'm brand new here, I belong to a different forum (I probably can't name I'm guessing) that deals specifically with performance boats but I can't get any help there because no one really runs volvo's. Here's the setup. 2004 292 Formula Fastech. Twin Volvo DPS's with 5.7gxi 320hp Catalyst engines. About 175 hours on engines and drives. According to the gauges I'm turning only 4800 rpms at 54 knots with twin f9's (figuring rpm's are correct, or at least hoping). Figured I'd prop down, which was an expensive proposition. I just ran it with f8's and literally no difference. Couldn't really tell if I had more acceleration because it's not like I ran them back to back with the f9, I was lacking in that aspect in the first place. But no more RPM what so ever or speed. Literally went right to the 54 max knots and hung there. I've never seen the rev limiter.

I have no experience with these Volvo props. I'm stumped. Do I keep moving down?

 

[steelespike]

Speaking generically Is your speed by gps? Your tach may be suspect being the same rpm with the F8s.
Can you do a test run on each individual motor by itself.Perhaps borrow a shop tach.

 

[bajaunderground]

I'm not familiar with the F9's nor the F8's. But I have the same motor (and probably drive) in the single form. The ratio on the drive should 1.95 and to me the F6 props were just a little lazy at my altitude (4,800'). My boat is 4,150lbs dry. What is the weight of your boat? Are both motors spinning the same RPM?
​I just switched from F6's to F5's, but haven't had it in the water yet? As steelespike suggested run on GPS (there's apps for any smart phone), then verify that the tach is actually accurate?

What did the previous owner offer as his top speed? I believe your WOT RPM's are 4,600-5,200? So you're at least right in the middle.