1990 150xp prop question

[Josparky]

I have a 1990 17ft hydra sport bass boat with a 1990 150xp SLE Model on it. Just had it rebuilt last year runs great. It has a old style Raker prop on it and WOT RPM is around 4900 and 62 on speedo. My prop guy tells me these motors between 1986 and 1990 run best around 4900 rpm but this is not what I am reading. Can someone help me out here. I found a good buy on a SST 2 prop that is a 23p would it do ok on this? He gave me a 21p aluminum to try on it course the motor was too high but it run well over 5500 if I wanted too I didn't run it over 5500 but it would go over that easy with that prop. So again what would the 23p SST 2 do over the 24p old style Raker? Book for this motor says rpm range 4500 to 5500 The raker jumps out of the water and pushes the boat around 62 mph on the speedo I am just wondering if it is ok to run it since it does jump out of the water and doesn't seem to be bogging the engine at all it just runs 4900 WOT. Was gonna check it today on GPS I had and got to fishing and forgot.

Thanks for any advice you can give.

 

[jestor68]

Re: 1990 150xp prop question

First; the Raker is designed for your bass boat, while the SST is not. Stick with a Raker or equivalent.

A 1.86 ratio with 24P at 4900 rpm works out to 55 mph at 8% slip. Gotta love those speedometers that read 61-62 mph.

What is your prop shaft to pad dimension? It may be worth playing with your set up to achieve a little more rpm/speed.

Your motor rated HP is reached at 5000 rpm. That's probably what your prop guy is referring to as the sweet rpm.

 

[Josparky]

Re: 1990 150xp prop question

Hey jestor68 thanks for the reply. I have moved it up and down with the jack plate and it is really not making any difference much at all. on the rpm or speed. very little on either. I am just concerned about if I am hurting the motor or not. Like a said it doesn't feel that it is under any strain I just want some conformation from others that running it at 4900 is not hurting it any. Since rebuild it has only seen XD 50 oil also I was told by the guy that rebuilt it that this was a better oil to use than the regular tcw3?

Thanks keep the info coming guys please.

 

[jestor68]

Re: 1990 150xp prop question

Hey jestor68 thanks for the reply. I have moved it up and down with the jack plate and it is really not making any difference much at all. on the rpm or speed. very little on either. I am just concerned about if I am hurting the motor or not. Like a said it doesn't feel that it is under any strain I just want some conformation from others that running it at 4900 is not hurting it any. Since rebuild it has only seen XD 50 oil also I was told by the guy that rebuilt it that this was a better oil to use than the regular tcw3?

Thanks keep the info coming guys please.

Your rpm is fine. XD50 oil is fine; as any TCW3 oil is.

 

[Josparky]

Re: 1990 150xp prop question

Thanks jestor68 for your replies greatly appreciated, makes me feel better. A lot of money tied up in this motor don't want to hurt it. If anyone else would like to chime in that would be great too.

Thanks

 

[Josparky]

Re: 1990 150xp prop question

Nobody else has an opinion on this? I thought this forum was lively.

 

[jestor68]

Re: 1990 150xp prop question

If you run your current performance numbers through the Mercury prop selector, it recommends a Laser II or Tempest Plus in 21 or 22 pitch.

 

[Josparky]

Re: 1990 150xp prop question

Well I know a 21 wont work already borrowed one and tried it too many RPMs with it.