prop
Printed From: CorrectCraftFan.com
Category: General Correct Craft Discussion
Forum Name: General Discussion
Forum Discription: Anything Correct Craft
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=467
Printed Date: September-30-2024 at 11:36pm
Topic: prop
Posted By: lectrician89
Subject: prop
Date Posted: June-09-2004 at 8:18pm
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Could anyone tell me the proper pitch prop for "69 Mustang w/289. I can't seem to get more than 3300 RPM with the one I have. The top end of the motor is new, so I assume it"s the prop.
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Replies:
Posted By: 66polyhead
Date Posted: June-10-2004 at 12:50am
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Does it have a 165 h.p., or a 210 h.p. Interceptor in it?
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Posted By: ken@ckbd.com
Date Posted: June-10-2004 at 1:10am
I believe the 289 was rated at 165 hp.
3300 RPM??? Well, when troubleshooting you should always start with the obvious: did you remember to hoist the anchor?
I had to ask! I crack myself up!
In all seriousness; I have to assume you have checked and double checked all the recent modifications you made to the motor? That would seem to be the logical place to start.
What size prop are you using now?
Is it the same prop that was on before the engine mods?
How fast did the prop turn before the engine mods?
3300 RPM sounds much too low to be caused by a prop. I could see you losing or gaining a few revs with a prop change - but not 1500.
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68 Mustang
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Posted By: reidp
Date Posted: June-10-2004 at 11:25am
I'm with Ken on this one in regards to the prop being the issue. I'm fairly confident that the original prop on this boat would have been either a 12x13 or 12x14 depending on which HP version of the 289 you have. It actually came in 165 and 190 HP versions as a 2-BBL and 210 HP as a 4-BBL. The lower HP models would have used the 12x13 prop. But even still, to only turn 3300 as a result of too much prop, you'd have to be turning a 12xsomething way high, like maybe a 16" or greater pitch. If you've got a speedo and the boat still runs 38-40+ mph for a 2-BBL version or 42-44+ for a 4-BBL, then I'd say your tach may be off, because only turning 3300 would certainly bring your top speed down significantly.
If the prop and tach are both correct, and the heads have recently been redone, then I'd check the rocker adjustment to make sure one's not to tight or too loose, causing one cylinder to be completely missing. 3300 is close to where you might drop down to on 7 cylinders. Just a thought.
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ReidP
/diaries/details.asp?ID=231&yrstart=1971&yrend=1975 - 1973 Mustang
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Posted By: 77stang
Date Posted: June-10-2004 at 3:06pm
the rule of thumb is that an inch of diameter is worth about 600 revs while an inch of pitch is worth about 200 revs. now i may be mistaken but i'm pretty sure the 289's ran 10 and 11 inch diameters. thus, if your running a twelve or thirteen you could be over proped.
call vince and get the scoop. he may refer you to miami nautique. regardless, you need to know what the boat should screw before you move on
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Posted By: 66polyhead
Date Posted: June-10-2004 at 10:11pm
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It's pretty simple to determine the diameter of the prop for most any inboard. Correct Craft uses this formula: center of shaft to bottom of hull - 15% of the radius of the arc for clearence. For example: center of shaft to bottom of hull = 7", 7"X.15"= 1.05", 7"X2=14", 14"-1.05" clearence= 12.95", or a 13" prop MAX.
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Posted By: Rick
Date Posted: June-11-2004 at 3:12am
This brings back mewmories of one of the more stupid things I've done. After rebuilding an olds 445 in a 16" hyatt I couldn't get more than about 3000 RPM. It took a mechanic to figure out I has switched the exhaust manifolds and they bolted on alright but 1/2 of the outlet was blocked.
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http://www.correctcraftfan.com/diaries/details.asp?ID=250&yrstart=1996&yrend=2000%20" rel="nofollow - 2000 Ski
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Posted By: 77stang
Date Posted: June-11-2004 at 4:40am
66polyhead
re: correct craft formula
simple - yes. well known - based on the prop size questions here and other inboard sites, i'm not so sure. anyway, thanks for sharing. i've jotted the formula and rational down to file. good stuff!
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