Do all dyno jets cross at 5250rpm? I had heard that as a mathmatical function that they all crossed at the same point. What would cause a graph to cross lower?

I got my car dynoed today and it crossed at 4600rpm.

 

It will cross at 5252 rpm if both the TQ and HP are on the same scale on the y axis. If the scales differ, the crossing point might be different.

 

Correct. It might make it easier to understand to say equal instead of cross. Even though the graphs might not cross at 5252, they will still be equivalent. Look at your graph, each side should be labled, and they will have different numbers at each labled point. Move over to 5252 on the x-axis go up until you hit the first line and check the number, being sure to use the correct side of the graph. Then go to the next line, and look at its corresponding value. It will be the same as the other one.

 

Wrong. If the scales differ it still crosses at 5252rpm, changing graph scales doesn't change horsepower formulas.

hp = tq * rpm / 5252

 

You are correct with your formula, but incorrect about the lines crossing at 5250 if the scales are different

The value of HP and TQ will always be the same at 5250, but depending on how it is graphed, it may not look that way at first. If the scales are different, the lines will not cross at 5250 on the X-axis. That's the problem with placing two scales on one chart.

Dan

 

All three of you have been right, except for the "Wrong." statement. Reread his statement.

-brent

 

Ya i suppose the crossing point will change but it should still be equal at 5252.

 

Yes, Serene, I realize the equation. I was referring to the display of the graph only, not saying the formula changes.