Reply
 
Thread Tools Search this Thread Display Modes
 
Old 10-12-2016, 03:40 AM   #1
Lt. JG
 
Join Date: Apr 2014
Posts: 21
Question Props & wot

Long story, but suffice to say I replaced both engines in my year 2000, 3700 SCR due to water intrusion. The new engines are 7.4 liter, 454's, which are about 320 actual horse power each. I was wondering what the specs are for WOT rpm's in the 3700? Also, what is the approximate top speed for the 3700 (I understand the premise about fuel tank fullness, the amount of fresh water/holding tank, number of people aboard, weight of equipment, etc.)? At this time, the original props are only giving me 3600 rpm's at WOT. I am thinking that different props with different pitch may give me more rpm's.

In addition, where would be a good place to obtain the new props?

Thank you in advance for any thoughts or suggestions.
__________________

Sailboattraitor is offline   Reply With Quote
Old 10-12-2016, 11:22 AM   #2
Admiral
 
mmwjr's Avatar
 
Join Date: Feb 2012
Location: Essex, Maryland
Posts: 10,176
Default

Did you ask the mechanic that replaced the engines what the WOT should be? I would expect it should be the same for these engine no matter what boat they are in which is 4400 - 4800 rpm.

Changing pitch lower will help also how many blades are the props? If 4 or 5 you can also consider going down one blade.
__________________

__________________
1997 Silverton 362, 7.4 Crusaders
1997 2400 SCR, 5.7 Vortec / Bravo 2

Mike
mmwjr is offline   Reply With Quote
Old 10-12-2016, 02:34 PM   #3
Lt. JG
 
Join Date: Apr 2014
Posts: 21
Default

The mechanic did state the WOT rpm's should be around 4600. I have 4 blades on the props. Any thoughts on where to buy the new props?
Sailboattraitor is offline   Reply With Quote
Old 10-12-2016, 04:20 PM   #4
Admiral
 
mmwjr's Avatar
 
Join Date: Feb 2012
Location: Essex, Maryland
Posts: 10,176
Default

Quote:
Originally Posted by Sailboattraitor View Post
The mechanic did state the WOT rpm's should be around 4600. I have 4 blades on the props. Any thoughts on where to buy the new props?
I don't have any experience with buying inboard props.
__________________
1997 Silverton 362, 7.4 Crusaders
1997 2400 SCR, 5.7 Vortec / Bravo 2

Mike
mmwjr is offline   Reply With Quote
Old 10-12-2016, 05:22 PM   #5
TJK
Lt. JG
 
TJK's Avatar
 
Join Date: Jul 2015
Location: Connecticut
Posts: 42
Default

Your figures appear to be way off, i.e. over propped for those engines.

According to Power Boat Guide, "Twin 380 hp V-drive MerCruiser inboards cruise the Maxum 3700 SCR at 18 knots (26–27 knots top), and optional 370hp Cummins diesels
cruise in the mid 20s (about 30 knots top)."

Your new engines have less hp. Need to reduce the original prop pitch or replace them with new ones with appropriate size/pitch.

Any reputable prop shop will guide you to select appropriate prop size and pitch, if you can provide the info of your hull, engines, transmissions, etc. Try this;

https://www.miwheel.com/inboard-propellers/prop-it-now/
TJK is offline   Reply With Quote
Old 10-13-2016, 02:14 PM   #6
Moderator

 
shrew's Avatar
 
Join Date: Apr 2008
Posts: 5,588
Default

WOT on the 454, like almost all Mercruiser engines, is between 4400 - 4800. Ideally you'd like to be as close to 4800 as possible, without going over. Speed is irrelevant.

3600 rpm Max WOT would be overpropped. There is a balance between # of blades and pitch. Going to a 3 blade will increase max RPM's, so would increasing pitch. 4 blade props are not stock on that model. I would start with a 3 blad prop in the range of stock and see where are you are for Max. RPM's.
__________________

shrew is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Powered by vBadvanced CMPS v3.2.3

All times are GMT. The time now is 11:06 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2024, vBulletin Solutions, Inc.