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Re: Hey! Engine Guys! Question For You!
Originally Posted by oldandtired
I don't know what rpm peak horsepower occurs on your engines, but you should definitely see an rpm change if you are only changing pitch. If the props are different types, then that may be why you aren't seeing an rpm change. Your slip seems to be high. Assuming that you are using 1.5 drives, and using 51 mph at 5000 rpm, 23 pitch prop, that is 30% slip which is way unacceptable. Are you sure that your tach is right? How are you driving the boat trim wise? If you are driving it trimmed up with the proper attitude, then you really need to start with the prop (assuming your tach is right). Hook is always a possibility and is easy enough to check, so you may want to get a straight edge out and look at it, but 30% slip is ALOT.
Rene |
Re: Hey! Engine Guys! Question For You!
GOODT! Can you tell me the acceptable numbers on a leak down test ?
OLDANDTIRED! How can I correct slip? |
Re: Hey! Engine Guys! Question For You!
Originally Posted by jeff32
Both props are mirage, the difference if any is maybe 100 or 200 rpm max difference. Never checked tack with timing light at wot, I will. trim are 100 down, as soon I raise the drives, gets prop spinning and I loose speed. How can I correct slip?
Trim is all the way down?????????? That would be the answer. If you can't trim up, then you can't lift the bow and you're creating to much drag. On that old of boat(floating brick) the props should be way deep. That is a heavy boat--like 11k. Get some 22" Bravo1 4 blade props. |
Re: Hey! Engine Guys! Question For You!
1 Attachment(s)
here is a chart for leak down percentiges oviously the more she leaks down the worse it is all mtrs will leak down some
as for comp test you want all cyl to be within approx 10% of each other |
Re: Hey! Engine Guys! Question For You!
Correcting slip is all about having things set up properly in the boat, trimming correctly and having the right prop. Are you running trim tabs? What position are they in? If you are driving the nose down with them, that will really hurt your speed and raise your slip. If you blow out as soon as you start trimming the drive up there has to be a problem. My limited experience says that most boats like 1/4 to 1/2 trim. Experiment with the trim tabs and drive trim for a while. I'ld really be surprised if you are blowing out the mirages at 1/4 to 1/2 trim. I am assuming that this boat has the drives in the factory original location. If they aren't, then that's a whole different can of worms to mess with.
Rene |
Re: Hey! Engine Guys! Question For You!
old and tired,
you are forgeting to ask what kind of trim indicators,if factory stock 1/4 or 1/2 could be any thing according to who set them and if they knew what they where doing as you said if mech then he would be quoting a # best thing to do trim drives till they slip ( rev go up quickly ) then go down till they grab keep tabs up except to stop porposing if needed |
Re: Hey! Engine Guys! Question For You!
When running 30 mph roughly, even trimmed down 100%, the bow is so high! I have to use tabs to be able to see! then above that around 38-40, the bow goes down (no tabs). when I want to trim it, this is when slipping mostly occurs, but it also happens at 30 mph. Drives are in factory position. I agree the 22 4 blade could help. I'll try it out. and will do leak test this week. I'll keep you guys posted.thanks!
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