What a difference the right prop makes!!

[FreeBeeTony]

I was running about 3200 RPM at WOT on my newly rebuilt Mercruiser 165 IL6 with a 19" pitch prop. Last night I changed the prop to a 15" pitch.<br />What a difference!!! Came up on a plane alot faster/easier, seemed like the engine wasn't working as hard, the temp came down to a more reasonalbe level (~170 @ 3400 RPM). The temp was so high with the 19P that I had to remove the thermostat (I now reinstalled the thermostat). I am very happy with the results. I completely rebuilt this engine myself and now it's running great! Last night I had it up to 3800 RPM and I still had some room to go! Just thought I would let you guys know.........<br />Thanks, for all your input.<br /><br />Tony

 

[jimmmy]

Re: What a difference the right prop makes!!

Hi Tony,<br />What size boat? I have been having RPM problems with my 16 and a half 1989 Oliver (fairly heavy boat) with 3 L Merc. Tried everything so far. Running 19 Pitch prop abd can get to 2600RPM only. No problem 4500RPM in Neutral? Did your speed drop much with the 15P?

 

[magster65]

Re: What a difference the right prop makes!!

Great news Tony!<br />Jimmy, an inch of pitch is worth about 200 rpm and similar is an inch of diameter. If your boat does not reach the rated rpm (usually around 4300 rpm) it'll be slow out of the hole, have way too much load on it causing horrible fuel economy and the engine won't last.

 

[FreeBeeTony]

Re: What a difference the right prop makes!!

Jimmy,<br /><br />If you can only reach 2600 RPM I would suspect something else rather than the prop pitch. My boat is a '78 20' Grady White (~3500lbs). Make sure you're running on all cylinders and the timing is correct. Once you are confident the engine is running correctly, then I would try the prop pitch. For that engine and that size boat I think you should get higher than 2600 RPM's with a 19P. Also make sure you have the right outdrive, I think you should have a 1.84:1 1.98:0 gear ratio. Good luck.<br /><br />I learned alot from this board while putting my boat together........

 

[akriverrat]

Re: What a difference the right prop makes!!

jimmmy, you would get much better response on this problem if you posted new post describing the problem and how it started. looking back at your recent posts, if repropping helps it will only be masking the fact that the carb secondaries are not functioning properly.

 

[TonyS]

Re: What a difference the right prop makes!!

Hi Jimmy, I have same boat with 3.o OMC. I have 17 on my prop, and get to about 4,400 rpm & 34mph. You must have something going on.

 

[jimmmy]

Re: What a difference the right prop makes!!

TS<br />I have plenty going wrong....but no one can figure out what. Spent $1600 so far since I bought the boat 7 weeks ago and doesn't run any better! I'm going to post a seperate message ...again!

 

[galaxy]

Re: What a difference the right prop makes!!

Hey Tony,<br /> Very interesting to hear about the prop change. I just bought a re-manufactured Rochester 2 bl. carb and what a difference that made. By the way, I have the same engine as you do. As you were, I'm also only getting 3200 rpm @ WOT. I too have a 19 pitch prop. I've been trying to teach my son how to ski. No wonder that boy has a hard time trying to get up out of the water! I wasn't sure how far down in size I would need to go with the pitch, but if 15 is working good for you maybe that's what I need as well. I have a 17' Galaxy 747 model. Pretty heavy boat too. Hmmm... 747! I wonder if that's why they gave it that model #? LOL

 

[FreeBeeTony]

Re: What a difference the right prop makes!!

Galaxy,<br />Try the 15P prop, you won't be disappointed. Let me know how you make out. The IL6 is a great motor, with the right prop and outdrive!

 

[cobra 3.0]

Re: What a difference the right prop makes!!

I have a 17" pitch prop on a 16' boat with a 3.0 OMC Cobra. I also have a Stingray hydro foil installed above the prop. That Stingray will get your boat on plane in about 1/3 the time. The boat just jumps up on plane! Without it the nose of the boat points skyward for a while before shooting forward. Also, much more stable and quicker turns! It really rocks when the boat is loaded .