Mercruiser 5,7 speed

[Eric08]

Hi everyone,
I'm new to this forum which looks great.
I own a 1998 Maxum 2700scr, equipped with a Mercruiser 5.7 250hp. My max speed is 18/19 knots. I find that to be little. Do you think this is normal?
Thanks.
Eric from Barcelona

 

[Scott Danforth]

What RpM are you turning?

 

[Eric08]

What RpM are you turning?

3600/3700 max. My W.O.T is 4500/4800.

 

[Bondo]

Hi everyone,
I'm new to this forum which looks great.
I own a 1998 Maxum 2700scr, equipped with a Mercruiser 5.7 250hp. My max speed is 18/19 knots. I find that to be little. Do you think this is normal?
Thanks.
Eric from Barcelona

Ayuh,..... Welcome Aboard,..... That does seem low,.....
How long since the motor was serviced,..??
How long ago was the boat's bottom cleaned,..??
Which drive do you have,..??
What pitch prop, 'n at what rpms is Wot,..??

 

[Eric08]

Ayuh,..... Welcome Aboard,..... That does seem low,.....
How long since the motor was serviced,..??
How long ago was the boat's bottom cleaned,..??
Which drive do you have,..??
What pitch prop, 'n at what rpms is Wot,..??

 

[Eric08]

Ayuh,..... Welcome Aboard,..... That does seem low,.....
How long since the motor was serviced,..??
How long ago was the boat's bottom cleaned,..??
Which drive do you have,..??
What pitch prop, 'n at what rpms is Wot,..??

2 years since the big service.
New Antifooling
The drive ... Bravo 1 or 2, i don't know .
RPM Wot 4500/4800

Thank´s

 

[alldodge]

How fast does it run at WOT?

 

[Eric08]

How fast does it run at WOT?

The WOT is not reached. Max 3700rpm

 

[Scott Danforth]

Start with a compression test

 

[alldodge]

The WOT is not reached. Max 3700rpm

Ok, have a compression test done with a accurate gauge. A new motor will be 150 psi and worn out one is 100.

If your tach is accurate being 1100 rpm low you would need to reduce pitch close to 10 degrees

If you know what pitch your prop is that would help, along with with the drive ratio is

 

[Eric08]

View attachment WhatsApp Video 2022-05-17 at 21.03.16.mp4

 

[Scott06]

If your WOT rpm is accurate you need to reduce prop pitch or you have an engine issue.

Did it ever get more speed ? Was the drive replace with a different ratio?

Agree start with compression test and look at basic tune up items

 

[alldodge]

Agree
If this is a new to you boat then the most probable cause is the drive was changed with the wrong ratio. If this just started happening, then its a motor problem

 

[Eric08]

This is my WOT.

How to reduce prop pitch ?

H

 

[Eric08]

Accepter
S'il s'agit d'un nouveau bateau pour vous, la cause la plus probable est que la transmission a été modifiée avec le mauvais rapport. Si cela vient juste de se produire, alors c'est un problème de moteur

 

[Eric08]

Thank you guys.

 

[Scott06]

This is my WOT.

How to reduce prop pitch ?
View attachment 362137
H

To reduce prop pitch you have to change your prop to one with a lower numerical pitch. If you have a 15" pitch now and the engine was in good working order going to a 15" pitch would bring rpm up about 800rpm at wot

I would check the drive serial number on the drive matches the drive serial number on the flame arrestor cover you just posted the photo of. Drive serial is on the port side of drive just under the vent plug on side of upper