Correction factor over corrects?

[BobbyB]

Thanks for the video.
Can you correlate water tank temperature to engine power correction? In other words, when you say, "you find power during the day only to lose it overnight", is there a repeatable relationship between the power loss and increase in tank water temp?

I don't know beans about a dyno, but I have a buddy that builds race engines and has access to a nascar shops dyno. One time when I was at the shop, he was dynoing an engine & I got to thinking about the change in density & viscosity of the water in the 1000 plus gallon tank and whether or not that was corrected for. The reason I thought about it was I had just been working on a water cooled gun barrel and looked into the change in viscosity and density of liquids vs temperature. I was surprised by how water compares to other common liquids. God knew what he was doing when he created water, it is very neat stuff.

Almost certainly this is corrected for by the dyno manufacturer since the brake temp is displayed in the video. I did find it interesting that when the brake temp exceed 100 degrees the display turned red on the video. Do you know why it turns red?

[andyf]

Let me just say that looking at relative humidity real does not tell you anything.

59F - 75% Humidity = 0.377295 vapor pressure, 55.61 grains of water, dew point 51.08473

89F - 27.451% Humidity = 0.377298 vapor pressure, 55.61 grains of water, dew point 51.08490

Stan

I went back and looked over some of my dyno test notes and I don't think the actual moisture content changed much during the testing. The relative humidity dropped as the day got warmer, but as your example above shows, the grains of water didn't change much. So I don't think we can blame it on moisture.

Another thing I noticed when looking close at the data is that the engine uses more air in the afternoon when it is less dense. So when the air density is 0.073 the engine uses 900 cfm at peak power. But in the morning when the air density is 0.076 the engine only uses 875 cfm at peak power. In either case the engine is using roughly the same mass of air and is making the same power, but the correction factor says it is making more power in the hotter weather.

I'm almost positive that the correction factor is wrong. I just don't know if it is only for this engine for some reason, or if the correction factor is wrong for lots of engines.

I've read some of what Patrick Hale has written on the subject and he says that the correction factor is wrong for fuels other than gasoline due to the cooling effect so maybe there are other factors involved that the correction factor doesn't take into account.

[John Wallace]

Are you using alcohol?

[andyf]

Maybe. I'm running a 50/50 mixture of unleaded non-ethanol pump gas and Hot Rod 102. I do not know what is inside of the HR102. So the engine is not an alcohol motor, but there could be some stuff in the HR102 that makes it act that way.

[David Redszus]

HR 102 is a non-oxygenated race fuel. Do you change mixture from morning to afternoon?

Do you know the equation for the correction factor you are using?

Do you have morning temperature and baro readings
and afternoon temp and baro? By temperature I mean inlet air temp, not ambient or cell temp.

Is dyno water brake temperature constant? Oil and coolant temperature?

[andyf]

I came across some information that might solve this puzzle. Another dyno shop reported that they saw the same thing with the engine making more power later in the day even though nothing had been changed. They traced the issue to the load cell which was temp sensitive. They did a hanging weight test in the morning when the load cell was cold and then put a heater next to it. As the load cell warmed up the torque value increased. They said it was about a 10 ft-lb change from 40 degrees to 80 degrees which is almost exactly the difference that I've been seeing.

[RW TECH]

It's not uncommon to see hot rod water brake packages that correct up to an additional 5% over, and the J607 factor has more drift in it that J1349 or later standards. This can really add to the fun when you're testing a combination that is not acutely weather-sensitive & trying to recognize smaller gains & losses. This is also why some OEM's will only certify power of new production engines if the correction is less than 2%.

Do you have an air handler that can keep up with your engines? Definitely something to consider, along with a means to condition the air for temp and humidity.

[Strange Magic]

I'm almost positive that the correction factor is wrong.

You are correct, it is wrong. The situation is basic and simple to understand.

The OP states that in the morning the engine makes 700 and by the afternoon, with no changes it makes 720, and the air is worse. It's pretty darn obvious that the formula written for correction and how it works with the sensors, is flawed, or as mentioned a faulty sensor.

[andyf]

I'm lucky since this dyno is located near sea level and in a part of the country where the climate is fairly mild. We rarely ever see a correction factor that is more than 5% and a lot of the time the correction factor is in the range of 0.98 to 1.03. But even a 1% change on a 700 hp engine is 7 hp which is often in the range that people think is material. If I change intake manifolds and see a 10 hp change then that seems like it should be a positive change. But then if the engine drops the 10 hp as soon as the temperature drops it makes me wonder if there was really a change.

It is fairly easy to do a temp test on the load sensor so I'm going to do that next. If the load sensor readings change with temperature then I'll just need to come up with an additional correction factor. It would seem like the dyno mfg should have this built into the console calculations but maybe not. If I find a temp sensitivity in our load cell then I'll call the mfg and see what they say.