383 stroker

[gobuck]

I bought a new 383 stroker Mercruiser mpi fwc to replace an old 5.7 EFI Vortec. How can I tell if the motor is making 350 hp? The boat burns the same amount of fuel and reaches the same top speed. The new motor is suppose to be 90 hp stronger.

 

[hnt]

Are you using the same prop and are you getting the same WOT rpm? Did the new motor come with a matched ECU?

Something doesn't add up?

 

[alldodge]

Was this a complete MPI drop in?
Didn't use anything from the old motor?

 

[QBhoy]

Maybe proved wrong but I don’t think the 6.2 mpi GM is a 350hp engine. Maybe you are thinking of the new built in house merc 6.2 ?
anyway. I’m presuming it’s a whole new engie with all bits for it. Because your old efi (not mpi) is a whole different thing. So the 383 would not use any parts from it really.
anyway. You should see a fair difference regardless.
you should have went from 250/260hp to 320 I think.
if your prop is the same as it used to be...the new engine will hit the limiter easily and perhaps see no gain in speed. Is this mayne the case ?

 

[gobuck]

The new motor was a new Quicksilver 383 MPI FWC drop in. It is suppose to be 350 hp. The old props were 22 pitch and the old engine wide open rpms only went to 4100. When the new motor was fist tested it would get 4500 rpms with the same 22 pitch props and go 4 mph faster. The new motor is suppose to be between 4800 and 5200 w/o rpms. We switched to new 20 pitch props and got the rpms to 4800 but lost the speed gain. The old motor was suppose to be 260 hp and the new motor is suppose to be 350 hp. Not seeing the 90 hp difference.

 

[scoflaw]

What boat ? Could be hull design "horsepower sponge"

 

[gobuck]

Albemarle 247 Express

 

[alldodge]

Albemarle 247 Express

Your boat weight is 5800 lbs dry and at least 7000 lbs loaded.

I'm seeing, first motor was over propped.
What's the drive ratio, and which prop is being used?

 

[gobuck]

The 1st motor was over propped. The new motor was too. We changed to 20 pitch props. The Bravo 3 is 2 to 1. I am not looking for more speed. I don't understand why 90 hp doesn't get more speed. The boat at full throttle only uses 25 gph of fuel. I would think that 350 hp would use closer to 30 gph.
I have Merc Vessel View installed. I need to find the serial # on the motor. I am not sure the one that the dealer gave me is correct.

 

[alldodge]

The serial number on a reman is of no use except Merc warranty.

Thanks for the ratio and prop info
Should have asked for speed numbers and if its using a GPS or boat speed-o?

If your reaching 40mph at 4800 with 20 pitch that would be 12% slip, so not bad. Now if your only getting 36mph then that's 21% and not good

Is the hull clean?

 

[alldodge]

Do agree going from a 305 to a 383 should push the boat much better. I tried similar going from a 415hp 502 to a 530hp 509 and the real difference I see is getting on plane. The boat comes up fairly quick, but top end didn't change much at all.

After changing drive ratios, then going back to my old 2.0, and trying different props, I went from a 24 to 26 B3 and hat's the best I can get. My boat is just to heavy for one motor

 

[gobuck]

40 mph with the new props. The old motor was a 5.7 efi with 1050 hours and fresh water cooled. It ingested Barnacle Buster and died. The new motor isn't a Reman. It is a brand new 383 unless my dealer isn't correct. I paid for a new motor!!!

 

[alldodge]

A virgin bore brand new stroker is a 377 cu in, a reman stroker is a 377 bored .030 over and equals 383 cu in

Merc sells a new (what they call) 6.2L but is actually 6.17L 377 cu in,
A true 383 is 6.27L which takes a 350 block and bore it .030 over

If it is a brand new 350hp new 6.2 then the WOT is listed as 5000-5400 rpm. This is a CAT (catalytic converter) motor so it has CAT exhaust as part of the manifold and Merc does list it as 377

If its a new reman 350hp 383 then the WOT is 4800-5200 rpm. Uses standard exhaust manifolds and no CAT and Merc list as 383

Its all nits and does have much to do with what were dealing with now. Just info to for you

Since your not seeing any issues on vessel view, and there are no codes, then I would lead toward its boat/hull design and trim angle.

Might be able to have the props checked to see if they are in tune, and can add some cup. Anything done with a prop if the efficiency is increased, then the rpms will lower. It does get me that there should be more top end, even if its small, there should be some.

 

[gobuck]

Thank you for your thoughts. It is nice to hear others thoughts/ideas when dealing with this.
serial # 1g700664

 

[alldodge]

The serial checks out, and does show up at the Merc parts place
https://www.mercurymarine.com/en/us/parts-and-accessories/parts-catalog

It list the pistons but not the block. Its also in the Reman listings

 

[Scott Danforth]

the 383 with a flamed engine cover is a remaned motor with either .030 over or .040 over pistons.

 

[alldodge]

You know if you came with the first post and had not been to the dealer and asked them, there would be more comments of to check timing, fuel pressure, pulling plugs one at a time to see if there is any effect, and scanning for codes

 

[Scott Danforth]

being a MPI engine, does mercruiser limit power for the first 10 hour break-in period?

 

[alldodge]

being a MPI engine, does mercruiser limit power for the first 10 hour break-in period?

Have not heard that one, but it should be taking it easy for the first 10

 

[QBhoy]

Ok. 20” on a bravo 3 twin prop then ? Strange pitch maybe ?
so it’s not a 383 stroker. It’s the new merc built engine ?