Engine Height RPM Gain - The Hull Truth

cabman · 07-07-2009, 06:33 PM

How much rpm gain can I expect from changing my motor height from the #2 hole to the #4 hole? Up two holes.

CapnDean · 07-07-2009, 07:03 PM

Not enough info: Assuming that your motor is 2 holes 2 low..... then you should see an increase of a 100 - 200 rpm. BUT...that can depend on the prop you have as well. It is possible to be under or over pitched to the point that raising the motor won't have much affect.

cabman · 07-07-2009, 07:08 PM

Thanks for the input CapnDean. Here is a post I made on another forum:

My new to me boat and motor, a year ago, came with a Stiletto 19p prop. It's performance seemed fine at first. Fully loaded, 5600 rpms, 42 mph. As I became more familiar with the set up, and with some research, I am sure my motor is to low, in the number two hole, and I'm not sure I have the right pitched prop. Will raising the motor two holes improve my rpms enough? I can fully trim now with no blow out at WOT. I have a friend with a Stiletto Adv II (ST10317) he's trying to sell me. Will this be a better prop for me? Will it even fit my motor? Or, Is raising the motor enough? Any input will be appreciated.

CapnDean · 07-07-2009, 07:12 PM

Raise the motor and see. It's easy to do and undo if you experience blow out. THEN see what your rpm is

kitebuz · 07-07-2009, 07:27 PM

You'll need more detail - which engine, which boat, what are your wot rpm & speed now, and what pitch prop are you running.

As a sheer guess, I would say you will see @ 150-200 rpm gain.

eggsuckindog · 07-07-2009, 08:06 PM

It kinda depends on which motor you have - 4 strokes like to go 6K but alot of 2S are at their best about 5500

As stated above about 200, it will also make the boat run different and better properly set up - you may be able to go up in pitch depending on the motor which will help cruise

Need to know what motor

cabman · 07-07-2009, 08:35 PM

Yep, sorry to leave that out. Hydra-Sports 202dc 200hp Yamaha 4-stroke. Thanks for the input folks!

peteorlando · 08-14-2009, 02:20 PM

I have the same boat i bought 2 months ago with a Yamaha F250. It was mounted in #3 hole and was only getting 5200 at WOT. I raised it one hole to the #2 and am now getting 5300 consistent and up to 5400 on glass. Still running the Yamaha SWS II 21" though. Top end didn't increase at all and i'm still at 48 to 49 mph. Thought this boat would fly with the 250 on it. Kind of disappointed. But the price was right. Need to try to swap out props and see what that does. Everyone is telling me this motor should be turning 5800 to 6000 WOT.

240 Coastal · 08-14-2009, 02:43 PM

peterlando,

I suspect you need a 19 pitch prop whiich in theory should bring your rpm's up to about 5800 at WOT. This should give you a much better hole shot and improved fuel economy.

Tom