Correct way to prop 165hp straight 6 mercruiser?

[Jerzyfine]

What is the correct way to prop my 165hp straight 6 mercruiser to get maximum rpm out of it?

 

[Bondo]

Re: Correct way to prop 165hp straight 6 mercruiser?

What is the correct way to prop my 165hp straight 6 mercruiser to get maximum rpm out of it?

Ayuh,... Welcome Aboard,.... Ya use the Pitch that allows it to run Wot, at good trim, at the rated rpms,...

'bout 44/ 4600 rpms in yer case I believe,...

 

[Fleetwin]

Re: Correct way to prop 165hp straight 6 mercruiser?

That engine doesn't like a lot of RPM's but has plenty of torque.

Most I've seen run at about 4300 RPM's tops. The props have rounded blades that I call "elephant ears".

 

[Jerzyfine]

Re: Correct way to prop 165hp straight 6 mercruiser?

Right now I'm getting 30,000 RPM. The engine is a 1973.

 

[jestor68]

Re: Correct way to prop 165hp straight 6 mercruiser?

You select the prop size(pitch) that will allow the motor to operate within it's recommended WOT rpm range; which in your case is 3900-4300 rpm.

I believe you meant 3000 rpm; not 30,000 rpm; since your boat's tachometer doesn't read that high.

If you need to adjust pitch size, do so assuming that an inch of pitch change equates to about 150-200 rpm change.

If you need to increase your rpm, you go down in pitch.

You likely need to remove the prop to read the size stamped on the prop hub so you know where you're starting from.

 

[steelespike]

Re: Correct way to prop 165hp straight 6 mercruiser?

What size and type of boat?
We can help you better if you get us the prop size,and do a lightl load test run to get us the wot rpm and gps speed.
Do you trim up for maximum speed? Does the boat respond to up trim?
Is the prop in good shape?

 

[Jerzyfine]

Re: Correct way to prop 165hp straight 6 mercruiser?

It's a 18.5' Searay runabout. I'm getting 3000 rpm and average 25mph. She does respond when I trim with the side padles. The prop is in very good shape. I have to go to the dock and take the prop off to see the size. Btw I want to thank you all for your help I really appreciate it.

 

[steelespike]

Re: Correct way to prop 165hp straight 6 mercruiser?

Is your boat a "Stringer"the outdrive doesn't have trim? I believe you can fine tune the setup.
And I guess the tabs will help some.

 

[Jerzyfine]

Re: Correct way to prop 165hp straight 6 mercruiser?

Not a stinger and its a I/O motor.

 

[steelespike]

Re: Correct way to prop 165hp straight 6 mercruiser?

So do you trim up for the best speed?
What are the "side paddles" you speak of?
If you have trim tabs your best speed will likely be with the tabs fully released.
We need your prop size.