mercruiser 165 prop suggestions?

jkcyranoski

Cadet
Joined
Aug 19, 2008
Messages
9
I have a 1971 Mercruiser 165 (inline 6) and am looking to see what people with similar setup run for a prop.

I currently have a beat up aluminum 13.5 dia x 21 pitch prop that I would like to replace. I am leaning toward a 19 pitch, as I think it should plane out faster and get more RPMs than it currently is. But, I found a really good deal on a stainless 22 pitch, so I am tempted.

My boat is 17ft, about 1800 lbs.

Thanks for any help/suggestions!
 
D

DJ

Guest
Re: mercruiser 165 prop suggestions?

That engine doesn't like anything over 4300 RPM.

Prop it to run at that 4300 at Wide Open Throttle (WOT).

You need to know your WOT RPM now to make a determination of whether to go up or down in pitch.
 

jkcyranoski

Cadet
Joined
Aug 19, 2008
Messages
9
Re: mercruiser 165 prop suggestions?

Sorry I forgot to include that in the original post...I am not getting even 4000 RPM, closer to 3700. I have read from other forum posters that my WOT range should be 3900 to 4300, sound right?

So this would suggest go 19, if I have gathered accurate info about pitch change affecting RPMs.

I guess I was just looking to see what people with a similar setup have found to work for them.
 
D

DJ

Guest
Re: mercruiser 165 prop suggestions?

Sorry I forgot to include that in the original post...I am not getting even 4000 RPM, closer to 3700. I have read from other forum posters that my WOT range should be 3900 to 4300, sound right?

.

Yup. Figure one inch of pitch equals 200 RPM, up or down.

If you could prop it to be able to turn 4000-4300, it doesn't mean you have to run it that fast.
 

carver63

Recruit
Joined
Aug 9, 2009
Messages
4
Re: mercruiser 165 prop suggestions?

I am brand new to owning a boat and am having issues with props. I have a 16.5 Glassmaster and will not trim easily and bogs the engine down tremendously. From what I have read so far, I need to increase the pitch.

This is everything that I can find on information so far:

weight 1750
WOT 4300
length 16.5
v-hull
current prop -48 78120 A40 19P (serial number?)

I have not been able to hit the WOT at all because it just is not able to. What I want it to be able to do is trim out fast and cruise easier in the 3800 range. I'm not into speed whatsoever, but others in the family want to be able to ski behind the thing once in a while.

Any help that anyone can offer will certainly be welcome!
 

hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: mercruiser 165 prop suggestions?

Jk, welcome to Iboats prop forum and we will try to help you as much as we can but without more information no one can help you, and I will tell you I need more information than anyone else. But if you would like my help fill this form out and I will help you as much as I can, if you would prefer to not go to this much trouble there are other people who will help you.

Iboats Boat and Motor Info
1. Year, make and model of boat
2. Length, width and base weight of boat, look for boat decal on back of boat
2a.What is the recommended HP for your boat
3. Number of people and gallons of gas normally on boat
4. What do you use the boat for
5. Is it a Deep Vee and if so how many degrees of deadrise
6. Year, make and model of motor
7. HP and gear ratio of motor IMPORTANT
If you don?t know the ratio, you need to pull the plugs out and put a piece of tape across the prop and the lower unit and then cut it between the prop and the housing and turn the motor until the tape lines up with each other, it is easier if two people do this, so one can watch the prop while the other counts the revolutions of the motor
8. Manufacturer?s recommended Wide Open Throttle (WOT) range
9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches
10. Is it a bass boat or does it have a pad bottom
11. Does it have a hydrafoil, dolefin or trim tabs
12. Make, model, diameter, pitch and whether SS or aluminum prop
13. WOT RPM and speed from your current prop and how much gas and how many people were in the boat for the test data and is the speed by GPS. If you do not have a tach you can buy a Tiny Tach for $ 50
14. Are you at sea level or a higher elevation, give us the elevation in feet
15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way, checked compression, and looked at the plugs and checked spark, all of the foregoing could be the reason your prop is not attaining full RPM
16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop
17. Does the prop show any damage that you can see
18. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations
19. If you are trying to attain a better cruising speed and fuel savings or trying to attain a faster speed I will want you to take your boat and run it with 1 or 2 people and give me the RPM and speed readings starting at 3,000 RPM in 500 RPM increments all the way to WOT.

REMEMBER, The numbers I give you will be NO better than the information you give me

The only thing I ask of you is to come back and give me a report of WOT RPM and speed for my database.

H
 
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