Torque Ratings for Optimax

[Maritime_Eng]

Hello-

I am working on a project and would like to know what the real world torque numbers are for a Mercury 250HP Optimax. Does anyone know this information? Any info would be great thanks!

Don
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[Prof. O/B]

Don, we can not determine maximum torque of the 250 HP Optimax without the knowledge of what the HP is at any given RPM. The formula for torque is:

Torque (in Ft. Lbs.) = HP X 5252
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RPM

Where an engine makes maximum Torque is at the point of maximum Volumetric efficency. Max. Volumetric Efficency is when the air flow has achieved proper inertia (speed) to start ramming the charge into the cylinder. There is a caveat to this, in that as the air flow becomes efficient, you start encountering the problem of the "physical" time you have to charge the cylinder. Let's look at an example:

A GM LT1 motor makes a maximum HP of 300 @5000 RPM. Yet it's point of maximum Torque is 340 Ft. Lbs. @3600 RPM. If you were in the car you would experience maximum accelleration at the 3600 RPM range, as the Torque dies off you would want to shift to the next higher gear. If we were to look at the torque at 5000 RPM we could plug-in our formula:

Torque = 300 HP X 5252
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5000 RPM

When you do the math you will find that the torque is now at: 315.1 Ft. Lbs.

You would have to have a Dyno Chart telling you what the HP was at 3600 RPM in order to determine the torque at that RPM.

On your Merc 250, you know that the engine is making max. HP power @5750RPM. So:

Torque = 250 HP X 5252
--------------
5750 RPM

At that RPM the engine is making 228.3 Ft. Lbs. Of Torque, but again, we can not tell where max. torque is unless we have a Dyno Reading in 100 RPM increments to calculate where maximum torque is. I hope this may be of some help to you................Prof. O/B

[150aintenuff]

there was a dyno chart of the 250 on mercs website at one time when it came out. but it was HP only.... and who knows if it was even truthfull or just a advertising piece that doesnt hold any real world valid data... but I would assume the peak is around 280-300 ft lbs around 4000 RPM.. i couldnt tell you if that is anywhere close but a seet of the pants feel says it is somewhere around there...