Take a look into what the atmospheric conditions (and therefore the correction factor) was during these runs. The SAE J607 equation is linear only to +/- 7% correction. Based on the differential between the BSFC figures reported and calculating the BSFC with the corrected horsepower, it would appear the correction factor was around 1.15x (+15%), which is too high.

In my long experience with dyno charts, typically if the correction factor is jacked, the BSFC's are lower. When ever I see BSFC's into the .300's, especially well into the .300's, 99.9% of the time the correction factor is way higher than it should be.

I'll have to look at this sheet more carefully and see what my brain can wrap around. I'm not too excited/interested to do so though. So maybe I won't. LOL.

Edit in: again, I can't remember if I ever see a four stroke into the .900's. Even on a first pull with no tuning. 2 strokes, yeh.

This data suggests that the measured horsepower is lower than the corrected horsepower. Looking at 4500 rpm on Engine #2, 268.8 lb/hr of fuel flow divided by 436.1 Hp gives a BSFC of 0.616 lb/Hp-hr off of the corrected horsepower number. To arrive at the reported BSFC, the measured Hp would have to be lower.

In response to what I said earlier, I do remember a few 'stupid' high BSFC's. Had to dig thru my slow cranium.

Fuel system on motor on dyno had return fuel system. They just used one flow meter instead of two.

With a return style system and one fuel flow meter, you are only readiing what the fuel system is flowing, not what the engine is using.

In a return system you want Meter 'A' measuring fuel flow going in and Meter 'B' on the return measuring what is returned. You simply set up software to be 'A' minus 'B' . This will tell you what engine is actually using for fuel.

Now, back to reading what you have posted....

I've seen the "A minus B" issue before as well. Maybe the OP can comment on how the fuel system was plumbed. Notable is there is a lot of variation in the fuel flow data, more than I'm accustomed to.

Just got off the phone with shop, the fuel system is not a return system so that's ruled out. I told him how everyone is ragging on the high BSFC numbers and he's going to look into his notes. He said they tried different jets but where he left it was where it was best. I also mentioned about the power valves and he was upset to hear that all four blocks had provisions but his guy somehow missed it. He'sl also going to pull the AFR charts once he gets a break.

We are not ragging on them (BSFC's).

They are brutal !

Point blank.

I have seen where there can be some variability in the fuel flow figures, as carburetors tend to fill the bowls in "gulps", rather than flowing a constant flowrate. That still doesn't explain the high BSFC's, though. Be sure to ask about the atmospheric conditions the engine was run at, and the correction factor applied to the measured data.

Here’s a 496 build I did a few years back and has the same guy dyno it. This seems a lot more along the “normal” side of the number readings so I know this guy knows how to get it right. NautiSouth, I’ll ask him these questions. Could these carbs actually be that bad but still run as good as they did on Sunday? Once I lower the primary jets they should clean up even more. Either way I’m stuck with these for the rest of this season.

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Lowest BSFC at Peak Torque.

Most all in the mid .400 range.

All good.

Did I mention your present Motors BSFC's are brutal ? LOL.