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buck202

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I have a 1988 four winns 200 Horizon 5.7 with an OMC cobra drive. This boat originally had a 4.3L, the previous owner changed the engine to a 5.7L. This boat runs well but can easily push 5500 RPM. I only ran it up to 4800 RPM at 30MPH. The service manual says it should be 4200-4600 RPM. It currently has a 14.25 x 21 SST prop. I would like to get the RPM down to the correct range. Does anyone have any idea what prop would get me to that area. The boat is mostly used for water sports and cruising. Top speed really isn't a factor. Thank you.
 
when he changed from a V6 to a V8, did he change the pulse switch on the back of the tach?
If you have 21 now and only go 30mph, I don't think a prop swap will get you where you need to be- probably need different outdrive gears. You could try a 25 or 27, but those things are brutal for holeshot. The good news though, is that they exist... because the V6 Johnson and Evinrude outboards use the same props and 27's weren't uncommon for bass boats. There's even 29's around. However, out of the hole performance is going to be yours to discover.
A 24 or 26 Raker is probably what I would seek out - the Raker's came in even number pitches and have vent holes to add some slip out of the hole and get the engine wound up to where it makes torque. I have a Raker on my 175 Slickcraft and it works well on my i/o despite them really being for outboards.
Props are really only all-round efficient between 15 and 23P
 
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I would guess he didn't change the pulse switch. So my next question is, what is the pulse switch and what does it do? I only went 30 MPH because I didn't want to over rev the engine. It would have went faster with no problem. Thank you for the reply.
 
if you look on the back of the tach there is usually a switch for 4/6/8 cyl or sometimes different terminals to attach the grey wire to. Find out what brand of tachometer and google it if not obvious from the markings on it.

A tachometer reads the spark firings per time and converts that to rpm. A V8 has 1 more spark per revolution (not two) than a V6 therefore the inaccuracy.
 
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I will look at the back of the tach this weekend. Its a factory tach in the dash. I know the p/o didn't change the gear ratio in the drive. Thanks for all the help so far. I'm headed in the right direction.
 
buck202 said:
I will look at the back of the tach this weekend. Its a factory tach in the dash. I know the p/o didn't change the gear ratio in the drive. Thanks for all the help so far. I'm headed in the right direction.
Click to expand...

I had an Inline6 with a 19p, used a 23p prop on a 4cyl outdrive, lots of torque, too much speed sometimes at idle, nice cruise range.

There are a couple good Marine NAV and GPS apps for Android Phones that will show GPS Speed, if you have one !!
 
Looked at the tach yesterday, it was still set to 6cyl. I changed it to 8cyl. I didn't get the chance to run the boat due to the weather, but I can assume it will be good to go now. Thank you all for the help!
 
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