Switch props to increase rpms but...

[ParallaxBill]

...still only got 3400-3500 WOT RPMs indicated. "Indicated" is the key here.:$

I had switched from a 13.75" X 21" pitch SS prop due to a lack of WOT rpms to a Vortex 14.5 X 19 but today on the lake I got the exact same WOT rpms with only two adults verses four on my previous test of the boat.

Lesson learned?
Yes, my tach was accurate until it got to 3400 rpms then it stopped indicating further. I tested it running up to 3400 then once it stopped it would keep climbing in "heard" rpmsat full throttle. How much?, I don't know yet but the engine sounds better, (stronger but not strained) with the 19" prop compared to the older 21" SS prop. Could be the difference in passenger weight as well.

Now to find a good affordable tach to replace my "rpm limited" tach to find the real WOT rpms.

Just thought this info may help someone not to trust a tach just because it is known to be correct at idle speeds. 33 year old boats are fun! It's running GREAT!!d

 

[kenmyfam]

Re: Switch props to increase rpms but...

Always best to verify RPM with 2 tach's so you know if you are correct. I am no expert on this and the other more experienced guys out here will give you a much better answer but increasing the diameter and decreasing the pitch may well give you the same result as your previous prop. What does everyone else think ???

 

[ParallaxBill]

Re: Switch props to increase rpms but...

I verified the idle rpms but I couldn't verify the WOT rpms.

This was the prop the iboats rep recommended. Diameter shouldn't have as much effect as pitch from what I've heard here. Either way, if the old prop was fine the new one could still be used as a cheap spare. Nothing lost so far.

 

[tiller7104]

Re: Switch props to increase rpms but...

Hey don't throw away the good old ear LOL If you are experienced and you know your engine than your ear is a great indicater. I am very relliant on my tach to moniter performance but know body knows your outboard the way you do !!

 

[kenmyfam]

Re: Switch props to increase rpms but...

Hey don't throw away the good old ear LOL If you are experienced and you know your engine than your ear is a great indicater. I am very relliant on my tach to moniter performance but know body knows your outboard the way you do !!

Right on with that statement. You do develop an "ear" for how your outboard is performing. There are certain cruising speeds where it just sounds right and like it is enjoying itself so to speak !!