Help with RPM
 

I just purchased a Sonic with twin 500 EFI's that has the stock Bravo 28 props. The problem that I'm having is that both motors will only turn 4700 rpm at WOT with a light load. These props should be turning closer to 5200 rpm. Anyone have any suggestions of where to start looking to get the rpm's up t where they should be?

What size sonic? There are a few ways to get the rpms up. Prop size (possibly a 26P) labbing the 28's, Gear change in drives (Not likely) It all depends on the boat size, weight and drive placement.

how do you have the drives trimmed? Has anything changed from before???....hit anything with the props? put any dings in the blades? Can you verify that the original owner ran at those RPM's before you on those props? maybe he did a switch-a-roo on ya before you picked it up??? (hope not) .....maybe you need to adjust toe-in/toe-out on the tie-bar??? lots of variables here that can affect things! :)

It is a 358 Sonic. I'd rather not go to the 26 props as I think I would loose some top end..

As for the drives I had them fully trimmed out when I did a run. The props are in great condition, no dings or anything. I can't verify what the previous owner ran at I only know that Sonic tells me I should be running close to 5200 with these props.

It doesn't by chance have
1.36:1 ratio drives ?

jt

I don't know - XR Drives - hopw would I find out if it had 1.36:1 ratio and if it did what would that mean?

Usually, the ratio is on the
l/h decal on the upper unit,
it will say 1.5R for a 1.5:1 ratio,
or 1.36R for a 1.36:1 ratio.

If you have a 1.36:1, your
propshafts are turning faster than
the more common 1.5:1 ratio drives,
thus, you have to use a smaller prop
pitch than if you were running a 1.5:1 ratio.

jt