I would use real world testing to determine where the engine is done at. In most cases, RPM = speed so if prop testing shows more speed at say 5,400 RPM than 5,100 RPM then in fact the motor is not "done" at 5,100 RPM.

Many things affect the maximum rpm of an engine. Cylinder head , camshaft, valvetrain setup, intake manifold, timing, compression, etc.

On ramos45's build, it was not a maximum effort all out HP build. It was a basic 454 mag upgrade, meant to run on the same octane level, and leave the option open for a future blower build, which he happens to be adding at the moment.

My point of posting it , was you can make respectable power out of a 454 on 87 octane. 500+ ft lbs at 3000rpm is not anything to turn your nose at.

I actually think it was a good combo. It did not have oversized hogged out intake ports, a generic camshaft , etc. If more power was the goal then yes more compression and more cam would have increased the output quite a bit.

With the addition of the small superchargers , he should have a nice 625-650hp setup out of what started out as some 365HP mags. There is more than 1 cylinder head choice, one intake choice, 1 carb choice, 1 cam choice, for a nice engine build.

In regard s to bsfc, its reading is not what the actual air to fuel ratio is of the engine. For the bsfc number itself to be accurate, the device measuring the flow of fuel has to be calibrated. If it isn't, the numbers are worthless.

A roots blown engine making 800hp will have high bsfcs than a NA engine making 800hp, due of the parasitic losses from driving the roots blower. Not because its "richer" air fuel ratio. Like sb said, its a measure of how much fuel the engine needs to make xxx horsepower. It's a good tool to tell you how efficient your engine is from a design standpoint, but not really a mpg standpoint, although that could help the end result as far as economy.

I would not use bsfc numbers to tune my carbs. Jmo. Disclaimer I am not a dyno operator nor engine builder. Just what I've been told on how this stuff works.

With the engine, yes. Anything that effects efficiency, which everyth effects, effects BSFC.

But not the Dyno. BSFC is lbs fuel used per horsepower. That's it.
The brake measure hp (torque actually) and the fuel flow meter measures fuel flow.

Software does not intervene with it other than dividing horsepower by lbs of fuel used. Just a simple calculation, with again, no other intervention.

What I was getting at SB, is that accuracy of the fuel flow meter itself, needs to be verified. Also, RPM per sec during a ''sweep'' test, can have an influence on what you see on bsfc readings. Faster the sweep, the more 'lag" in data you can have.

Fuel flow turbines, meters, etc can give inaccurate readings. The reading on the actual dyno sheet, is only as good as the accuracy of what is measuring the actual flow of fuel for the dyno pull.

http://www.land-and-sea.com/dyno-tec...alibration.htm

If the BSFC numbers on that dyno sheet, are in fact accurate, than that engine sure had alot of power on the table. If something was that far off to cause the BSFC numbers to go that high, and still make over 500HP from a 9:1 454 with a mild cam, I'd like to see what it would do if it was tuned right.

Heres Ray from Raylars take on this topic found here

http://www.offshoreonly.com/forums/g...uestion-2.html

I think you might be making a skewed comparison here without enough input calibration. BSFC's are very diificult to calculate on most dyno's , especially if the fuel flow rate sensors and such have not been exactly calibrated before the runs. When measuring fuel flow in Lbs. to calculate exact BSFC's the slight variations in fuel flow can skew the BSFC calculations quite a bit. That being said, I don't think if your wide band O2 sensors are calibrated and giving accurate readings that can be relied on that you would ever want to run a 1000Hp huffer at anything beyond 12.0 to 1 for sustained persiods in a boat. What were the EGT numbers at these readings and were they rising under a sustained pull with a slow rpm per second rate?, or did they level off at a sustainable number? Our dyno work tends to show that there obviously is a point where a fat motor will give up some power and rate of rise in power under loads, but its a pretty small percentage and the totally overfueling beyond whats needed for the blower life will definitly effect ring life and oil life.
I suspect the loss in boat performance here as it does in many boat powers is a hull, drive or prop issue.

Best Regards,
Ray @ Raylar

It (dyno sheet you posted) was a 300rpm/sec sweep. Not a 600rpm/sec sweep. The 300rpm/sec test will have lots less data lag.

A bunch of operators will do their first series of runs on 600rpm/sec sweep just to get things going and slightly tuned in, and then switch to 300rpm/sec sweeps to get more exact data and thus get it (the motor) more dialed in.

One's in a hurry (ie: not much tuning , if any) will many times just leave it at 600rpm/sec sweeps.

You win

Win a round table discussion ? What ? Really ? Oh boy.

Tha's all this is. A RTD. A new acronym...lol.

Not gonna keep arguing this subject regarding BSFC numbers on an engine I had nothing to do with. If one believes that a BSFC readout on a dyno sheet can be without erroneous readings, so be it.

Winter stays long this high Jeremiah.......