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what does it mean when the graph is choppy. its on the HP line and the TQ line. had it dynoed a while back but never asked this question. hopefully with some of you guys help i can smooth out these lines when i go back to the dyno.

thanks
mike
 

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Originally posted by si hunter:
what does it mean when the graph is choppy. its on the HP line and the TQ line. had it dynoed a while back but never asked this question. hopefully with some of you guys help i can smooth out these lines when i go back to the dyno.

thanks
mike
<font size="2" face="Verdana, Arial">Not much info to go on here, but let me give it a try.

First if the torque fluctuates then the HP HAS to fluctuate also. HP = Torque * RPM / 5252.

So, HP is just a function of torque. Another way of expressing power. That's why they cross at 5252 RPM.

About the choppy graph. A Dynamometer is not collecting data in a continuous stream. Instead it samples the data at a certain rate. If changes occur between the samples then the lines on the graph appear to jump to the next data point. Most plot programs allow for some data smoothing. In other words the program will look at the samples and fill in for the time not collected which will smooth out the lines. Actually smoothing algorithms are more complicated than that, but that's the basic idea. I know that the DynoJet program has 5 levels of smoothing that can be applied to the graph.

Also the scale of the plot can affect how smooth it appears. Lets say that your actual torque starts at 100 Lb/Ft and peaks at 135 Lb/Ft and then drops to 95 Lb/Ft. If you plot that graph on a scale from 0 to 200 lbs, it will look much smoother than a graph displayed from 80 to 140 lbs. Does that make sense?

I don't know if this covers your situation without seeing the actual graph.

Some choppiness could be normal, alot could be a problem.
 

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Discussion Starter #3
thanks for the info. its was measered on a dynojet. i wish i could show you. i guess that would help even better.

mike
 

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Other than the awesome explanation Blue gave - Here's my $.02.

I've seen choppiness in a graph before cause by a few things:

1 - Bad plug wires, old plug wires that don't have the proper connection or cannot transmit the proper information to the dyno will cause the graph and power to appear choppy

2 - Bad plugs, causes misfires and chops and dips the graph in places where it misfires

Bad plugs were the case on unfocused's dyno:





- Drew

[ 12-23-2002, 12:19 PM: Message edited by: focusownerskid ]
 

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in addition 2 the bad plug and plug wire issues. some dynojets (especially if their stuff has had some time on it), dont play nice w/aftermarket wire sets, some of the older inductive pickups dont like the thicker wires. this was the culprit 4 my dyno runs (FR 9mm wires) when it took 4ever 2 get a steady readin, and then upon the pass its has a wealth of choppy-ness. suggestion is good set of plugs gapped properly 4 ur application and then a healthy set of stock wires 4 the dyno passes. then plop ur aftermarkets on when ur done.

-Ult
 
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