150 HPDI ideal WOT RPM?

[akholmes]

2003 150 HPDI hung on a 2120
80 hrs on the motor w/ good compression on all 6. Factory prop... not sure of pitch off top of my head.

What is my ideal WOT RPM?

Thanks for info!

 

[DaleH]

[No more than[/b] 200 to 300 off of the MAXIMUM RPM range as specficed from Yamaha. The range given is typically 1,000 RPM wide, like 5,000 to 6,000 and some dealers will leave the boat setup with a prop that turns 5200 RPMs ... but for BEST performance and longevity of that motor ... you want to be as close the top end as you can.

On my motors, I insist on being no further away thatn 200 RPMs off maximum, in the Spring, 1/2-tank of fuel, 2 guys and with a clean running bottom. You lose RPMs once the bottom gets fouled and in the hotter Summer air ...

 

[Mokee]

Same boat and motor/prop. Yamaha says max rpm ranges 4500-5500. As I recall the sticker on the motor says 5350.

When I trim up the motor to get max rpm, she starts to porpoise over 5000 @ WOT. Top end on my boat with gear and 1/2 tank of gas is 37-38 mph SOG measured on GPS. In ideal conditions she cruises @ 27-30 mph in the 4000-4200 range. The motor was raised one hole and a Permatrim added on advice from Andy @ SIM.

 

[scalywag05]

I also have a 2003 2120 with 150 hpdi. I am the second owner and it originally had a 13 and 3/4 X 17 black stainless prop. Would turn 4800 max. Went to a 15 1/4 x 15 and got up to 5200. Speed and cruise is just like Mokee
(don't quote me on the diameter sizes, but this is what I remember doing. Definitely dropped from a 17 pitch to a 15 and went up in diameter)

 

[DaleH]

If it were mine and I still only turned 5200 RPMs, I'd try another prop or would tweam that ine to turn higher ...

 

[akholmes]

Yeah man I'm stuck at 4800rpm 34mph sog. Might look into a reprop. SS or alum?

 

[DaleH]

Yeah man I'm stuck at 4800rpm 34mph sog. Might look into a reprop. or alum?

If you do NOT re-prop it ... thst motor isn't going to run as well or last as long. One recen newer member here had his 250hp blow the powerhead within 1500-hours of use, where he was turning 1K !!!!!! off of the maximum rated ROMs.

Go SS unless you boat where rocks are more prevalent than fish ... like up on the coast of Maine.

 

[akholmes]

Thanks for the advise man! I have always been a mostly 3/4 throttle kind of guy. Hardly ever pushing wot. Should I run wot more often?

 

[DaleH]

Thanks for the advise man! I have always been a mostly 3/4 throttle kind of guy. Hardly ever pushing wot. Should I run wot more often?

On ANY motor, 2 or 4-stroke, specially when some of the day was spent trolling, I would do some high speed runs on the way back in to help 'burn out' any crud that can build up from excess idling or trolling.

But remember, the reason to TEST the motor at WOT for maximum RPMs is to SET and check you have the right pitch prop installed ... that does not mean you need to run up there all the time. In fact, on 2-strokes, the best fuel efficiency is typically 4K RPMs +/- 200. But you can easily cruise at 4500 to 4800, but fuel burn starts to go down ...and fast once above 4500 RPMs.

At WOT a 2-stroke typically burns about 10% of the rated HP of the OB label, so a 225hp motor will burn about 22.5 GPH at WOT. I tested my 250hp Suzuki 4-stroke the other day at WOT and I was burning 23 GPH (read via my fuel computer).

Lugging a motor, like having a boat propped to turn no more than 5K RPMs (when she should be turning up to 6K RPMs) is THE FASTEST way to kill a motor less not adding or having any oil ...