I have a question regarding the Fuel-A (lbs/hr) listed on a dyno report. From what I understand this number reflects the pounds of fuel burned per hour at the specified rpm. The numbers seem high to me. I'm looking at a report on a 496 stroker burning 150 gals an hour at 3500 rpms - that would be about 25 gals an hour. My 454's burn 18 - 19 gals at the same rpms. Now I know the stroker should be higher, but that much?

Does the dyno apply the max load to the engine at each rpm? If so that could explain the higher fuel burn on the dyno as opposed to a boat hull that may have less load at the same rpm due to hull efficiency. Or - is that really the number to expect?

Thanks

Probably going to be close. Might be a little on the high side, but shouldnt be too far off i wouldnt think.

What HP was it making at 3500 rpm? Should give you the bsfc for that RPM, another way to figure out fuel burn and efficiency.

It takes fuel to make HP. I suspect the numbers are correct. Chances are the 496's are making 20% more HP at 3500rpms and using about 20% more fuel.

The dyno run will be WOT with the dyno pulling it down to 3500. In a boat you are only at part throttle at 3500. Big difference.

.5 lb/hr/hp is the # for gasoline engine fuel consuption
as I recall.

I think the 150gal/hr should be 150lbs/hr, which would be ~23gals/hr. So that seems right.
http://www.land-and-sea.com/dyno-tec...using_bsfc.htm

Now that does make sense. That would certainly account for the higher fuel burn number.

The BSFC is .47 - about 341 hp at 3500.

Yup, It takes a half a pound of fuel to make one horse power as it was explained to me !

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I agree it takes about .5 lbs of fuel per hp. But you can rev the engine at the dock to 3500 rpms and burn a lot less fuel than running the boat on the water with full tanks and load of people at that same 3500 rpms. You're obviously using more hp to get that 3500 rpms when you're loaded down on the water. So it would make sense to me that the dyno Fuel burn numbers are when the engine is fully loaded to max hp potential as opposed to being partially loaded when running out on the water where you may not be utililizing the max hp at a specific rpm.

I think bobl hit it on the head when he stated "The dyno run will be WOT with the dyno pulling it down to 3500. In a boat you are only at part throttle at 3500. Big difference"

For curiosity I took my prop curve analysis that calulates prop load and the needed engine hp needed to run at a specific speed and rpm. The fuel burn numbers came out on the money when using the .5 lbs per hp formula. The intersting part is I used a lot less hp at 3500 rpms in my boat than the dyno did. I would think I could adjust the prop to utilize more of the avaialable hp.