This website uses cookies. By clicking Accept, you consent to the use of cookies. Click Here to learn more about how we use cookies.
Accept
Reject
cancel
Turn on suggestions
Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.
Showing results for 
Search instead for 
Did you mean: 

I have a relatively new to me 2006...

Charles_III
Guest Contributor

‎05-02-2021 08:15 AM

I have a relatively new to me 2006 Sundancer 40 w/ 8.1 S Horizon MerCruiser gas engines @ 370 HP each and am concerned that the engines may be under performing - new fuel pumps, refurbished fuel injectors, replaced all heat exchangers, upgraded spark plugs, tune-up, annual service, new bottom paint, new shaft seals/cutless bearings, etc. Cruising: 19 kts @ 4200 rpm. WOT: 25 kts @ 5000 RPM. And the starboard engine burns ~ 15% more fuel per hour than the port. Your personal experience, feedback and insights would be very much appreciated. Thank you!

0 Likes
9 REPLIES 9

wingless
Rising Contributor

‎05-02-2021 08:30 AM

Welcome to the forum.

It may be that a more detailed basic engine examination is required. Start w/ the correct factory service manual (FSM) for the engine.

My suggestion is to check everything, all very basic stuff. Here is a partial list:

Rotor
Distributor Cap
Timing
Spark Plug Condition (Insulator Visual to Indicate Burn, Ceramic Cracks)
Spark Plug Gap
Compression
Fuel Pressure (Multiple / All Test Conditions)
Engine Fault Codes
All Vacuum Hoses Clean / Clear (Mine are Cleaned Annually)
Flame Arrestor Clean (Mine is Cleaned Annually)
New Fuel Filter(s) (Mine is Replaced Annually)
Remove / Inspect / Clean / Replace Intake Plenum (Mine is Cleaned Annually)
Engine Alignment
Propeller Tune / Balance (Mine are Always Prop Scan Class S)
0 Likes

Lar
Guest Contributor

‎05-09-2021 08:40 AM

Those engines are rated to turn 4200-4600 rpm max. 5000 is to high. If your tachs are accurate I would check the props for correct size.
0 Likes

Charles_III
Guest Contributor

‎05-09-2021 09:32 AM

Thank you Lars! Upon inspection, we learned that the prop stamp is 21 x 20 vs 21 x 22 per the parts manual. We are having the props re-pitched as we speak!
0 Likes

cbruck
Guest Contributor

‎05-09-2021 09:51 AM

I have a 2010 390 DA with the same engines but I have sterndrives and at 4200 rpm I run about 34 mph. Mine redlines at 4500 rpm. The 496 were made for torque and unless they are well balanced internally I would be very cautious about running them above 4500 rpm. Hopefully your props are the answer as it sounds like you have done most everything.
0 Likes

Big_mike1
Guest Contributor

‎05-24-2021 05:33 PM

U have one prop at 21x22.5 and starboard at 21x22
0 Likes

Big_mike1
Guest Contributor

‎05-24-2021 05:34 PM

That’s the way Searay did it
0 Likes

Ooh_La_La
Guest Contributor

‎05-30-2021 05:03 AM

I’m replacing my props on Monday, 20x20 on my 454, 400 EC. I’ll let you know if I get back some knots
0 Likes

Shark
Guest Contributor

‎07-04-2021 06:01 AM

We had a 1992 499 express and I replaced the props with 20x20 on our 454's and gained 4 miles per hour at cruise (3400rpm). I could cruise at 24 to 25 mph at 3400 rpms. It was a great improvement because before at 3400 rpm we only did 21 mph. The correct props make a world of difference! These were 4 blades props by the way. Our wop rpms were 4000.
0 Likes

greatscott
Guest Contributor

‎07-04-2021 06:16 AM

you have a cruiser (key word) if you want the motors to last keep it at 3200 rpm ,remember its a big boat w gas motors 16 to 17 mph is all u should be doing just saying
0 Likes
Copyright © 2024 Khoros, LLC