As Andy is saying, just because dyno numbers differ, does NOT mean anybody is lying. Things are NOT exact, don't care what some care to preach. I dyno most motors, NOT in an attempt to wear it out on the dyno and have a cool sheet to show people, but for the purpose of making sure it is sealed up, the carb is right and it shows to make about the power it SHOULD, based on the parts.
I built a 632 for a guy a few years ago, it made X power on a certain dyno. The next year after a freshen, we ran it on a different dyno. It was down 80hp and he was concerned. I pointed out that it burned the SAME amount of fuel, at the same air fuel ratio on both dynos, so regardless of what the sheet says, it makes the same power it did. One was a properly calibrated Stuska, the other a properly calibrated Super Flow
So which one was correct. Only one of the HP numbers can be correct. Or, I guess both could be wrong. How would you know, other than time slips?
I get it that there are variables, and that would account for SLIGHT differences in outcomes. But to try to get me to believe that one guy loses 80 HP and that's NOT an issue...well, you won't.
What do you want me to say. They were not my dynos, or in my shop, nor did I calibrate them. Would you not agree, that if the motor burned the same amount of fuel, at the same A/F and it moved the same amount of air.......that it made the same amount of power, even though two dynos read different power numbers? All I know is that even with a dyno sheet that said the motor was 80hp down, the car ran the same as it always did. I didn't dyno it after the freshen in an attempt to make more power. Just to break it in, make sure it was sealed up and everything was OK. After the first power pull, I to was concerned about the loss of power, but after looking at the fuel flow numbers, I knew the motor was fine
Ok Monte, I understand EXACTLY what you are saying. I get it. My problem is that (especially in the situation you brought out) that an 80 HP loss is HUGE when you did nothing but freshen it up. Then you say that it ran exactly the same with the lower HP number as it did before.
If you KNOW the car weight (that means it was weighed with corner scales and not on a freaking truck stop scale) and you now have the ET and the MPH you should know, for a FACT, which dyno was closer, if not correct. You should know, that for a certain MPH, you can generate a MINIMUM ET, and the ET and MPH should be very close. So comparing those numbers you should be able to figure out who was bullshitting you and who wasn't.
If you freshen it again and take it to a third dyno, and it drops say, another 70-80 HP what would you think? Just another junk dyno? More semi useless numbers (I understand BSFC, BSAC, IMEP etc)? Who says that the other numbers pulled from the dyno are correct? If the HP numbers are off, how do you know the BSFC numbers are correct, other than they they were similar? What if the engine was down 80 HP and the BSFC was .55? The AFR's were close. But at the track it ran the same?
At some point we either have to say the dynos are junk (which I KNOW some guys hate dynos) or someone is lying.
I don't understand why this is hard to grasp. If everyone measures diffently, you could never build the Hubble telescope or anything technical like that (engines are rather crude by aviation standards, and cave man when compared to space program related projects).
That why SAE wrote the standards. And we know there are reasons to fudge the standards. But damn, you guys are throwing around 80 HP (way more in some cases) like it's nothing. It's no wonder some guys who post their HP and ET numbers in their signature and they can't add up. Unless the car weighs 4800 pounds or the dyno was junk/wrong or the operator caused the numbers to lie.
You can't have it both ways.
