Speed and RPM's 400EC

S

Searaybio270

Active Member
Jul 8, 2010
1,058
Bush River on the Cheasapeake Bay
Boat Info
1996 EC, Garmin 3210, Dinghy - Seadoo Jet boat with twin 85 horse. Fun and Fast.
Engines
7.4 MC 360 HP each
Westerbeke 7KW
I have been tracking my trips and I keep coming up with the same numbers or very close. Last night 8 of us went for a cruise down the river, across the Chesapeake Bay to Fairlee Creek and after some food, conversation and drinks we came back.
So:
8 adults
200 gals of fuel
3/4 water
Dinghy with motor
Cooler with ice an beer

3200RPM 23.5 MPH.

Can that be right?
 
Sounds about right....
Are you thinking it's too fast or slow ??

I've found the 400EC to be quite fast for the given HP, it will cruise faster than some smaller dancers with the same HP and handle the waves better too!

Gota love it..
 
Last edited:
Ok, so now I have to wonder about my boat. I am only getting about 20mph at 3400 rpms. Props were reconditioned at the beginning of the season. Hull should be clean and in good shape.

Occassionally I get more speed at that rpm, but that would only happen if I am running with a tidal current in my favor. If the tide is against me I will slow down to as much as 18mph.

I have the 7.4s with carberators so I know they are not producing the horsepower that others likely get.

Should I be concerned? Should I look into anything?
 
My '93 400EC with 7.4's would cruise at mid-20's at 3200-3400 rpms. I was pretty surprised at how much slower the 420 was with 8.1's.
 
Searaybio270 said:
I have been tracking my trips and I keep coming up with the same numbers or very close. Last night 8 of us went for a cruise down the river, across the Chesapeake Bay to Fairlee Creek and after some food, conversation and drinks we came back.
So:
8 adults
200 gals of fuel
3/4 water
Dinghy with motor
Cooler with ice an beer

3200RPM 23.5 MPH.

Can that be right?
Click to expand...
If it is right, then what a great speed to run those 454s at for longevity of the engines. Great hull design. I was surprised by how fast my 370 express was with 454s. With full fuel and water it cruised around 23 knots at 3500. I would keep pulling the throttles back on a long cruise as fuel was used and the boat got lighter. For their size these ECs are not real heavy, and in calm seas are fast.
 
h_gerry said:
Ok, so now I have to wonder about my boat. I am only getting about 20mph at 3400 rpms. Props were reconditioned at the beginning of the season. Hull should be clean and in good shape.

Occassionally I get more speed at that rpm, but that would only happen if I am running with a tidal current in my favor. If the tide is against me I will slow down to as much as 18mph.

I have the 7.4s with carberators so I know they are not producing the horsepower that others likely get.

Should I be concerned? Should I look into anything?
Click to expand...

3400 rpm and 20 mph....is a bit slow.

But, if you can rev out to max rated RPM....just go with it and enjoy.

I think the old tach's were referencing are prone to errors..
 
7.4 horizons in our '98 400DA are doing 20kts (23.5mph) at 3,100 rpm's as I type this. 1/2 tank water, 1/3 gas and 2 adults.
 
3200 RPM is where my 4 barrels open and fuel consumption doubles.
My top speed when I got the boat was 22 knots at 4200 RPM but it was empty
Loaded it goes 18 knots at 3800 RPM
 
Air O'Nautical said:
3400 rpm and 20 mph....is a bit slow.

But, if you can rev out to max rated RPM....just go with it and enjoy.

I think the old tach's were referencing are prone to errors..
Click to expand...

At the beginning of the season I was topping out at 4100rpms and getting a little over 26mph. Now I am reaching 3800ish at top end. I am sure I have a seasons worth of grass and slime on the hull.

You our are right about the tachs, when the syncronizer says the engines are running the same rpm the tachs are off by 50-75rpm.

New guages and and flow scans are on the to do wish list!

and yes Mark, I am going with it and enjoying the heck out of it!!
 
Thanks everyone for the input. I should have added but I am also sure that most of you know my boat is fuel injected. My friend had a very nice 380 Sundancer mayb a 2008 or 2009 and he would run at 3400 or better just to stay close. So for me I was just wondering as this has been the best boating summer I have had with the boat in 6 years of owning it. I wonder if getting divorced in 12/2015 has anything to do with it. Hmmmm...............

Thanks again, everyone.

 
h_gerry said:
At the beginning of the season I was topping out at 4100rpms and getting a little over 26mph. Now I am reaching 3800ish at top end. I am sure I have a seasons worth of grass and slime on the hull.

You our are right about the tachs, when the syncronizer says the engines are running the same rpm the tachs are off by 50-75rpm.

New guages and and flow scans are on the to do wish list!

and yes Mark, I am going with it and enjoying the heck out of it!!
Click to expand...


The Flow Scans are now! " Out of Business" Per phone my con. at 206-524-6625
 
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