Chassis dyno question.

[ponchoV8]

Does a chassis dyno use A/F ratio to calculate h.p. or is it strictly based off the wheels spinning the rollers? The reason I ask this is that I had my car dynoed about a year ago and with the cutout closed (264 h.p.) my A/F was a decent 11-11.5:1, but with the cutout opened (278 h.p.), the A/F leaned out all the way to 17:1; nonetheless I was still happy with the numbers I got for so little investment. I never had my car checked out since then but it has always ran fine. When I changed my plugs several months ago they didn't show any signs of lean conditions. So now I'm assuming it was the tech's equipment. I was told elsewhere that maybe the A/F probe might have sniffed some ambient air which could have given it a false lean readout. Therefore, I'm just wondering if the h.p. numbers I got is actually a true reading or if it was skewed because of the A/F probe? Thanks.

[Mars_302]

Nope. It just uses measure the a/f to let you know where its at.

[Buzman23]

Take a look at this...Horsepower vs. Torque . It might help you out a little in understanding this stuff.

[DrDirt]

It was the cutouts that were playing with your A/F ratio, Arnold. The Dyno A/F meter was just picking up and reporting the change. The location of the cutout is the culprit I think. Check with Dino or Marty, they can fill you in on exactly what is going on. I believe it has to do with the 4 oxygen sensors. If your cutout is between them, things get screwed up because the computer is trying to compensate.