need help i am lost

[rpatton]

I will try and keep this short but it a long story. First i have a 19 foot bowrider with a 3.0 omc and stringer drive 1985. I had theshifting cable go bad. And rather than put close to a grand into it a dealer i know and have delt withsaid that he would sell a used drive ready for the water for half . That is where my problem started with props. I had a 400 series and the replacement was a 800 so the prop i had would not work 13 1/4x 17 so he sold me a 15 x19 which i tred and could only get about 2500 rpm at wot so then he gave me to try a 15 1/2 x 13 and said the math he figured should get it to the 4500 i need. But guess what i still can not get above 3000. Am i screwed with this drive or what do i need or what is my best option. I realy need help hear and sorry this was so long

 

[Scott Danforth]

Re: need help i am lost

the gear ratios are different. you were better off leaving the 3.0 coupled to the 400 and just replacing the shift cable yourself.

 

[rpatton]

Re: need help i am lost

Thanks that is what i thought but when we checked the drives by rotating shafts the rotations where the same so the gearing should be the same. Is there anything i can do prop wise to get the rpms up closer to where i need them. Another question is can i do damage runing like i am

 

[spdracr39]

Re: need help i am lost

no and yes.

Tell him to put it back the way it was and i would not let him work on anything again as he obviously has no clue what he is doing.

 

[steelespike]

Re: need help i am lost

You could pull the plugs and count the rotations yourself. Mark the flywheel and prop and count the flywheel revolutions for once on the prop.A pain but the only way top bet sure its a prop/ratio problem and not a motor issue.
Wouldn't be the first with a plug wire off or throttle not opening all the way.Especially after some work.

 

[steelespike]

Re: need help i am lost

A 800 with a 3.8L is a 1.77 ratio the 400 3.0 is i.71 . 800 with a 5.0 is 1.41 ugh.

 

[steelespike]

Re: need help i am lost

If it can turn a 12" pitch up to 4600 not could produce 38 mph An 11 about 30.
Maybe he can just change the gears. If the 800 waqs from a 3.8 it should work.
What did he say the ratio was?

 

[rpatton]

Re: need help i am lost

He dis not say what the ratio was but i was rhere when we counted the revs of the shaft and the seem to be the same. i am sorry i realy do not understand the prop piches and how it all works. That being said can anyone tell me if i can get the rpms roughly where i need them and if not can i run it at a comfortable rpm without hurting anything. Pleaae be patient with me i am new to the io world

 

[steelespike]

Re: need help i am lost

OK lets assume the ratios are close to the same,that would mean the motor has a problem.
When counting the shaft revolutions it is in relation to one prop revolution.
Verify the motor is 100% If the motor is 100% your stuck and should not run it faster than fast no wake speed for any extended time.
It could cause engine failure over time.

 

[rpatton]

Re: need help i am lost

The revolutions where compared shaft to shaft. I tried a 15 1/2 x 13 this weekend and there is a much beter inprovement. At wot it is now at about 3600 rpm. I know this is still not right but i am thinking i might be on the right track. With this prop i can run pretty much where i like to run withut going to wot. I am wondering if there is a pitch any lower than the 13

 

[Scott Danforth]

Re: need help i am lost

A 800 with a 3.8L is a 1.77 ratio the 400 3.0 is i.71 . 800 with a 5.0 is 1.41 ugh.

the 3.0 and Stringer 400 were a 1.86:1 ratio.