DF 90 max rpm

[Panfish21]

I just purchased an Alumicraft navigator with a 2007 DF 90. It gets up on plane right now but it is at 5800 rpm at three quarter throttle. At full it is at 6500. Do I need a different prop? According to previous owner original prop. I thought I read that 5800 was about max for rpms for this motor.

[Moonlighter]

Yes, you are under-propped. You shouldnt rev to 6500.

Edit: HOLD fire on the info below - I am seeing conflicting specs on the rev range for the DF90 around 2007. I will do some more digging and come back to you.

Update: OK all the official Suzuki brochures around 2005-2008 show max rev range of 5500rpm for the DF90. So you are massively under-propped.

Do you know if it is hitting the rev limiter at 6500?? The signs that it is would be engine missing/hesitating.

You might need to take the current prop off so that you can check its size. Would normally be printed on the inner hub. Then you will have an idea of what change needs to happen to get you into the correct rev range.

Perhaps check and let us know what size and brand (Suzuki ?) and any other markings. And whether it is alloy (painted white usually) or stainless steel.

Normally, from the brochures I have just seen, the prop would be expected to be 14" diameter, and the pitch will be unknown until you let us know.

Possibly someone ignorant about Suzuki double reduction gearboxes put a 17" pitch on there, thinking that the 17" which is commonly used on other outboard makes would suit, when it will not suit a Suzuki on most boats. I would think you should probably have something like a 14 x 21 or, if the boat is very light, maybe even a 14 x 23. But we wont know that until you tell us what dia and pitch the current prop is.

Every inch of extra pitch generally gives about 200rpm, assuming that you stay with the same prop manufacturer, model and diameter.

Assuming that the motor is not hitting the rev limiter at the moment at WOT, I would suggest you get a prop with an extra 5" of pitch, if available. If not, then 4" more should bring you close which is OK. I assume also that you do not run around at WOT all the time!