Anyone seen power or dyno curves of the Mercury 350 Sci inline-6 engines? Or 400R?

[Ribber]

Hi, long-time boater and go-fast enthusiast here.

We have one boat with twin Mercury 350 Sci outboards and are considering some setup changes.. possibly a re-power to V8's.

I was wonder if anyone has seen any power curves or dyno graphs of the Mercury I6 engines? Information on the 350 Sci would be ideal but the regular 350 or 400R would be interesting too.

Any experience with best rpm, torque curves etc could be interesting. I'm trying to figure out some different loading conditions, empty vs full fuel and ballast etc. So the real question I'm trying to figure out is "if I'm forced to run the engine at full throttle but say 6000 rpm how much power do I lose?". So if it makes 350 hp at 6500rpm (guessing) how much does it make at 6000rpm? Hope that makes sense.

Thanks.

[Chaz]

Nice first post ... :thumbsup:

Almost all engines run their best just past peak torque till it starts to nose over.
You really don't want to tug the motor too hard at WOT. If its straining to hard against a load , you would be better off by freeing it up by putting a smaller pitch prop on it than take a chance of detonating , especially if your running a low octane fuel. It'll ping like my wifes car goin up the Palm City bridge .. :leaving:

This is just a generic dyno sheet for a 6 cyl BMW .
You can see (pretty typical) that the torque is within 10 ft/lbs from 3500 to its peak at 5000 rpm. Because horse power is a function of Tq x RPM / 5252 .. even though torque is falling off , it still continues to climb until it has just runs out of breath .. where no amount of rpm will make up for the lack of torque ..
The good news is that between 5700 - 7000 .. it makes pretty much the same power. I know this is not your exact engine .. but I'm sure its characteristics will pretty much mirror this graph … :)

https://i.imgur.com/n09KcXXl.jpg

[Todd D]

The more you spin it the more boost it makes! You must be near the limiter to see full potential

[JPEROG]

I know the 400s don't become happy until they are North of 6500 guys try to prop them for 7100 for the exact reason Todd mentioned "small displacement requires boost".

Joe

[Chaz]

For multiple parameters involved, you'll see why my first statement and graph is correct .
In my own experience , a high-helix retro 8-71 on a 522ci platform went 6.70 / 203 @ 38 lbs . At 52 lbs it went 6.70 / 203 .. and would shred a belt with-in 5 runs.
Why ? The simple answer is .. put a fork in it, its done … ;)


https://www.youtube.com/watch?v=jDKmITwNRZA