RPM redline

• May 22, 2022

• #1

Rivertender

Member

Nov 7, 2006

123

Tampa Bay

Boat Info

370 aft cabin S Ray 1997

Engines

Twin 454
Inboard

Had:

....heads

....manifolds

....risers

....injectors (on port engine)

...............on both my 454 Mercruiser engines

.....1,000 hours on the engines

.....Bottom is cleaned monthly.


Sea trial for repairs recently.

My port engine is maxing at 3400 rpm

Strbd engine is maxing at 3800 rpm


For sure, the 3400 is too low.

I am thinking even the 3800 rpm is too low.


I am feeling I should get 4,000 rpm anyway if not the 4200 to 4400 I expected



Question - in the event new fuel filters don't help....and .....my mechanic tells me that 3800 is all I am going to get from an older engine......................is this correct? Do you agree?

Thanks for any thoughts.

 

• May 22, 2022

• #2

S

scoflaw

Well-Known Member

Aug 10, 2011

6,395

cape cod mass, cape coral fl

Boat Info

1999 Powerquest legend 260 sx 502 mag
2005 Baja 242 islander 496

Engines

502 mpi Bravo 1
496 mag B1

No you have an issue. Did you check compression ?

 

• May 22, 2022

• #3

hughespat57

Well-Known Member

GOLD Sponsor

Sep 25, 2016

1,254

Rock Hill, SC

Boat Info

300 Sundancer 1994, trailered tri-axle LoadRite roller

Engines

Mercruiser 5.7 260HP Alpha One Gen II, twin

Agree not right and a poor answer from a pro
Compression check per @scoflaw
What props are on the boat now?
Compare to the OEM parts book shows 23x24

 

• May 22, 2022

• #4

Espos4

Well-Known Member

Jan 1, 2017

3,011

Long Island NY

Boat Info

2007 240 Sundeck

Engines

350 MAG Bravo 3 W/DTS

That’s a lot of repair work. Could be as simple as a couple of crossed plug wires on the port motor.

 

• May 23, 2022

• #5

Rivertender

Member

Nov 7, 2006

123

Tampa Bay

Boat Info

370 aft cabin S Ray 1997

Engines

Twin 454
Inboard

scoflaw said:

No you have an issue. Did you check compression ?

Click to expand...

Yes. Comp is good

MY mechanic has not stated yet that the engines are older ya da ya da, but I am wanting to be prepared in the he does do that.

 

• May 23, 2022

• #6

Rivertender

Member

Nov 7, 2006

123

Tampa Bay

Boat Info

370 aft cabin S Ray 1997

Engines

Twin 454
Inboard

hughespat57 said:

Agree not right and a poor answer from a pro
Compression check per @scoflaw
What props are on the boat now?
Compare to the OEM parts book shows 23x24

Click to expand...

Same props as always

Comp is good

Thanks

 

• May 23, 2022

• #7

Rivertender

Member

Nov 7, 2006

123

Tampa Bay

Boat Info

370 aft cabin S Ray 1997

Engines

Twin 454
Inboard

Espos4 said:

That’s a lot of repair work. Could be as simple as a couple of crossed plug wires on the port motor.

Click to expand...

Copy.


Thanks

 

• May 23, 2022

• #8

hughespat57

Well-Known Member

GOLD Sponsor

Sep 25, 2016

1,254

Rock Hill, SC

Boat Info

300 Sundancer 1994, trailered tri-axle LoadRite roller

Engines

Mercruiser 5.7 260HP Alpha One Gen II, twin

Rivertender said:

Same props as always

Comp is good

Thanks

Click to expand...

So you haven't changed the props, but what I am getting at is...
You got the boat around 2016
Has the boat ever made WOT RPM? 4200-4400
Why did you do all the head work? What were the issues?
While the heads were off did they check the bores with a micrometer to confirm they were still in spec?
Did they hone them at all?

Previous owners could have over propped the boat for any number of reasons.
Many think they can improve top performance by going a bit larger.
Or they bent the originals and put on what they could get a the time.