Prop - can't seem to find the right size

[jlinder]

Here's an odd one. <br /><br />First specs: 1988 Chapparal 198XL with (19 foot) with a 5.0L GM engine. Book specs for WOT: 4200 to 4600<br /><br />HISTORY<br />I had a 14.5 x 19 prop on it (boat had this on it when I came on scene). WOT was 3700. Worked on engine, did some work. WOT now 3900. Prop by now had some dings so I replaced it. WOT now 3950.<br /><br />Everyone said go to a 17 pitch prop, that would bring WOT up about 200-300 RPMS. Go a 14.5 x 17.<br /><br />WOT now 4900 ??? 19 pitch to 17 pitch changed me from 3900 RPMs to 4900 RPMs?<br /><br />Both props are michigan wheel vortex series.<br /><br />Any ideas?

 

[1981Baja]

Re: Prop - can't seem to find the right size

I would say the old prop may have been repitched but you say your new 14.5X19 has 3950 rpm vs. 3900 for the old prop. very interesting. I hope some others have ideas.

 

[LubeDude]

Re: Prop - can't seem to find the right size

I think the first prop was marked wrong, try another 19P.

 

[walleyehed]

Re: Prop - can't seem to find the right size

Strange.....<br />I believe I would suggest they same as LubeDude, But....if a new 19 is at 50RPM higher than your old one, That would indicate a correct pitch comparison. I would think there "may" be an issue with blade design on the 17"....does the cup look the same???<br />Are you positive the 2 tested props are 19????<br />We run a 21" SS on a 21ft cuddy wellcraft, 305 mercruiser, and it will turn nearly 5200RPM.<br />This is at about 3600ft above sea-level to boot.<br />I would have guessed a 21 for your rig.<br />Are we sure there are no engine issues left???<br />Verify the tach is correct also...we may be getting a bogus reading.

 

[jlinder]

Re: Prop - can't seem to find the right size

I checked the props. They are Michigan Wheel and the size is stamped into the prop, looks like it is part of the casting. I don't think it is possible for them to be miss marked.<br /><br />The first 2 were 14.5 x 19 (model 992004), the new one is 15 x 17 (model 992003).<br /><br />I will call Michigan Wheel tomorrow when they open. Just cannot figure out why I picked up 1000 RPM.<br /><br />Next question - there are 2 reasons for working to get the right prop. First is obvious - performance. <br /><br />The second is what it does to the engine. I have been told that to high a pitch and you load down the engine and put a strain on it. To low and you can over rev.<br /><br />I woudn't expect that 4900 would hurt a 5.0L GM engine (305 cu. in), but is there so different in a marine engine that makes 4900 a problem?

 

[walleyehed]

Re: Prop - can't seem to find the right size

When you Marinize an auto engine for marine applications, several things are changed and/or done that is not done to the auto version such as balance of the rotating mass.<br />Not saying I will recommend this, but we turn our 5.0 carbed version, 5500-5600 all the time with a 19. It's just over 1500 hours now, and a lower unit impact with a rock jetty at about 50MPH is the only damage we've had.....No engine issues.<br />Most of the time, we run the 21 on it though, unless we have a load of people or skiing...

 

[ramster]

Re: Prop - can't seem to find the right size

I have a glastron 195SX (18'7") W/220HP 5.0 volvo GL. Stock prop was 14.5x21 3 blade,turned 4600rpm 54 56 mph. Tried a Mich. Vortech 4 blade 14x20 and my rpm's climed to nearly 5000rpm, hit rev limiter, top speed was 52mph. Now running a Solas Amita 14x21 4 blade, now runs around 4500rpm havent had smooth enough water to gps top speed but have seen around 55 with a little more to go<br />So far my findings are to stay with same pitch from 3 to 4 blade, not drop like some people say.<br />Maybe if you switch to stainless with a lot of cup drop 1" of pitch.

 

[jlinder]

Re: Prop - can't seem to find the right size

I talked with Michigan Wheel, and they agree with me. Changing from the 14.5x19 to a 15x17 should only change WOT by about 300 RPM, not 1000.<br /><br />They said I can send it in for checking but not sure I want to bother with shipping and having the prop with them for 2-3 weeks.<br /><br />I might try a prop shop to verify everything.<br /><br />STRANGE

 

[vipzach]

Re: Prop - can't seem to find the right size

Jack, I think that 17 is too small for your boat, try a prop shop and see if they have a new 19 or maybe a 21 that you could go test out. I have gotten to know a prop guy around here that will let me try out props is I want to. Maybe you can get that lucky. <br />I have a 3.0 that is turning a 14.25 x 17 SS rapture prop. I think the 17 is too small for your 5.0!