Come in Walleyehead

[glass from the past]

Walleyehead, <br /><br />I need your help, you seem to be the man to talk to when it comes to props. Here is my question. I want to replace my prop as mine is stock and has a big dent in one of the blades. I have a 1979 15' Chyrsler tri-hull with a Chrylser "691 cc" 45 horse, matched from the factory, with out my motor the boat weighs in about 450lbs. I had a hydro-fin, but I am going to replace that with smart tabs. From what you were explaining in another post setting up with the wrong prop can blow up your motor from stress. I want some performance increase, but I need to be gentle on the hold Chrysler as the wife says this motor needs to last till her car is paid off. I have a 4 horse kicker and a minnkota for all my fishing needs, So I tend to use my 45 horse for gettin to the fishing holes and getting up and down the trailer. I do use the boat to tow the kids in the tube once in a while also. WOT is around 4600 RPM. What are your thoughts on the right setup as far as a prop and increasing the life span of the motor?

 

[rickdb1boat]

Re: Come in Walleyehead

Not Walleye,<br />But, what pitch prop are you running now? You need to get those RPM's up to at least 5300. The standard recommended prop is a 10-3/8 X 13-1/2. If you are already running this pitch prop, I would suggest that you have it repitched to a 11 1/2". Not that that will get you to where you need to be, but it will help. You will gain a couple hundred RPM's, though. Are you sure the motor is running up to snuff? You do not want that motor "Lugging" from running too little RPM's. Walleye will have more input soon. Let us know what prop you are running and if the motor seems to be running good. Compression check is where I would start. A 45 HP should have no problem turning the proper RPM's on a boat like yours.

 

[glass from the past]

Re: Come in Walleyehead

Hey Rick,<br /><br />I totaly appreciate your insight, you are always a help with my little Chrysler. I have wondered if that WOT RPM was too low, as many of the posts mention these 5000+ WOT RPM. I would say that it ran OK, it started up on the 1st or 2nd time, idled well, runs well through it's power band and it doesn't miss. The one thing that I did notice is that it does take it 30 to 45 seconds to wind up to it's full WOT RPM. Getting up to 4000 RPM is easy, but taking it up to 4600 + RPM takes a bit longer (seems labored). To answer your questions: <br /><br />A. I believe it is a stock prop, but I am unsure of that. How can I tell what pitch i have now?<br /><br />B. I went to that site you sent me for my impeller and I picked up a carb kit for the motor also. The fuel bowl had a minor leak, but that has been repaired. My carb is set to the rich side. The guy I got it from, set it that way to keep it at a low idle. Should that be re-set?<br /><br />C. I didn't decarb the motor last season, just threw in new plugs. Motor has now been decarbed, and fresh plugs installed, so that could help my WOT situation? <br /><br />D. I haven't checked the compression (will a regular automotive comp. gauge work?), but I did have an issue with a burnt plug wire so I had to replace them, I can tell you that I have very good blue spark that is equal on both cylinders<br /><br />E. The dent (bend) in the prop is pretty major, looks like the motor wasn't raised up and the blade hit something hard, can that effect WOT RPM's?<br /><br />Let me know what you think, my checkbook awaits your instructions

 

[rickdb1boat]

Re: Come in Walleyehead

Glass, the first thing I would do is replace the prop and I think you will have solved the bulk of your problem. The diameter and pitch should be stamped on the prop hub. You will have to remove it and look closely to see it if it's there at all. If not, a prop shop will know. They may also suggest a better pitched prop for your situation. An automotive tester will work fine. The type that screws into the spark plug holes is the best, as opposed to the kind that have a rubber end you just shove in there. If you have good spark, good compression, good fuel supply and a new prop, you should be good to go. Let us know how it turns out...

 

[rickdb1boat]

Re: Come in Walleyehead

Try here for prop:<br /><br /> web page They show a 10-3/8 R 14-1/2 as the repacement. You might also check the Michigan prop selector found HERE. They also recommend a 10-3/8 X 14-1/2" prop for your application.<br /><br />or I-Boats may have one. Check them out first if you like.

 

[glass from the past]

Re: Come in Walleyehead

Rick you da man,<br /><br />I was checking out both those links you sent me, but I have one more question for you. You are right on the money with the 14.5 pitch as the correct replacement. When I checked iboat.com I found several Michigan wheel props for my motor, now they list the same 14.5 pitch, but they also list pitches that range from 10, 11.5, 12.5 & 13.5. What effect do these other pitches produce. does going to a lower pitch create better holeshot and less top end speed or the other way around or what?

 

[rickdb1boat]

Re: Come in Walleyehead

Yes, a lower pitch prop will create a better holeshot, but you have to make sure you are not over-reving the motor at full throttle. I would not drop below the 11.5 prop. That will get you another 400-600 RPM's and should get you ALOT more perfomance out of your boat, without overtaxing it. I believe you should run that motor between 5000-5500 RPM's. The 11.5 should get you close if you are trimmed out right and the engine is running up to par right now. If all is right with everything else, you need to get those RPM's up to avoid Lugging the motor, which can lead to premature failure. A smaller pitch prop is the way to do that...

 

[glass from the past]

Re: Come in Walleyehead

If I drop down from 14.5 to 11.5, do I lose a lot of top end speed? If so what is your guess, 3-5MPH?

 

[walleyehed]

Re: Come in Walleyehead

Not to butt in here, as Rick has answered your questions well..<br /> As stated, to be "taking it easy" on the engine, the R's gotta come up some as RB has mentioned, you may have to live with a slightly slower boat with less pitch, but I have seen cases where the engine was unable to reach it's power band with too much pitch and was actually faster with less pitch, and "easier" on the engine in the long run.<br />If I were to add anything to Ricks comments, it would be to error on the side of low pitch and add cup or "bite" as needed, vs. removing pitch or cup, making the prop more "inefficient" over-all.

 

[glass from the past]

Re: Come in Walleyehead

Hey you two,<br /><br />Thanks for all your input on this question, I know this question does come up a lot on the forums, so I appreciate your patience in answering these questions over and over. I think I am starting to understand the science of props. Not only is it what makes your boat fast or quick, but it does quite a bit to control engine RPMs and overall effiecency. If I understand this right then, it seems like props are somewhat similar to tires on a car? Smaller diameter, quicker acceleration, higher RPMs at say 60 MPH. larger diameter, slower acceleration but lower RPM's at 60MPH. Selecting a prop is like picking tires, shorter tires (less pitch) = more acceleration and higher RPM's. Taller tires (more pitch) slower acceleration, but lower RPMs. So for a big diesel that turns low RPM, taller tires are OK as shorter would be hard on the engine. For a sports car that turns higher RPMs, too tall a tire is hard on the motor (engine lugs), so shorter is better. <br />I am going to start with the 11.5 pitch and see how my motor runs (get to that 5000- 5500 RPM) at that stage and go from there. I will order that prop today and let you know how it works out. <br /><br />Hey, thanks a again RB and Walleye

 

[roscoe]

Re: Come in Walleyehead

I can see it now.<br />"If you want to go faster, you need to put tall tires on your boat."<br /> <br /><br />Very good analogy, though.