Not reving high enough
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=4563
Printed Date: November-27-2024 at 11:12am
Topic: Not reving high enough
Posted By: 87Dominique
Subject: Not reving high enough
Date Posted: August-20-2006 at 6:11pm
Hi, I have a 1987 Correct Craft Dominique with a PCM 351. It has a 13 by 13 three blade prop but the engine only revs at 3400 RPM when the throttle is completley open and the boat is going about 40 mph, the manual says it should top out at 4400. I thought the secondaries weren't opening but I had my father drive the boat and I could see the linkage under under the secondary diaphragm move. I can't figure out the problem. The boat idles perfect, starts perfect, and accelerates perfect. I was wondering if anyone could offer any suggestions. Thanks
|
Replies:
Posted By: 77stang
Date Posted: August-20-2006 at 6:58pm
i dont feel like working the math (i seem to have lost my little spreadsheet that calc's it) but i dont think 3400rpm, 13" pitch, 1:1 drive will equate to 40mph especially when you consider slip. either you tach or your speedo isnt accurate.
-------------
http://correctcraftfan.com/diaries/details.asp?ID=1360&yrstart=1971&yrend=1975 - '77 Mustang 17
|
Posted By: 87Dominique
Date Posted: August-20-2006 at 7:46pm
3400RPM X 13" Pitch = 44200 inches per minute
44200 x 60= 2652000 inches per hour
2652000/ 63360(inches in a mile) = 41.86 MPH
The speedo may be off by a little but i think its pretty close.
|
Posted By: GottaSki
Date Posted: August-20-2006 at 7:50pm
nope, something is off, I'm certain
-------------
"There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing."
River Rat to Mole
|
Posted By: 87Dominique
Date Posted: August-20-2006 at 7:56pm
|
The speedo could be off but both of them say the same thing. Its unlikely that they're both off. THe Tach may be off but when the engine is idling it's right around 600 i think.
|
Posted By: 87Dominique
Date Posted: August-20-2006 at 8:14pm
I guess the tach could be way off but how fast do these boats usually go with 13 by 13 inch props. I just got the boat last week so i don't know if it ever went any faster. How would i hook up another tach to the engine temporarily just to find out for sure?
-------------
"The worst day out boating is better than the best day working in the office"
|
Posted By: KENO
Date Posted: August-20-2006 at 10:58pm
87 Dominique
Your math is right, but you forgot to take slip into account. You came up with it's theoretical top speed with no slip accounted for. Probably 15 % slip or maybe even 20 on that boat.
15% would then get you about 35 to 36 MPH. 20% would be about 33 MPH
4400 RPM would theoretically be about 54 MPH and with 20% slip you're at about 43MPH which would be about right for that boat/engine combination.
keno
|
Posted By: 87Dominique
Date Posted: August-21-2006 at 8:41am
Thanks I'll try a different Tach and use a GPS for the speed.
-------------
"The worst day out boating is better than the best day working in the office"
|
|