Hi All,
I was on a dynojet the other day and they used a tailpipe sniffer type A/F ratio meter to graph the results. I was wondering how accurate are these things especially since they are after the catalytic coverter?

Also, my car showed pretty lean results ~14.7 throughout most of the power band even though it just has an high flow cat and 2.25" exhaust and short ram intake on a OBD1 GSR motor with idle fuel pressure at 42 psi ( within stock specs ) with hose connected running 94 octane. However, it does have a small exhaust leak between the header and cat before the o2 sensor. Would this cause the A/F to read lean on the dyno's tailpipe meter? The dyno charts look fine and match up with other stock GSR motors; its just the A/F ratio looks too lean.

 

Fix your leak and then try again...........The vacuum seen between exhaust pulses could be mixing fresh air in, but there's no way to tell for sure other than fixing it. Also, you might be running slightly lean due to your performance mods. You should get an FPR and bump the static fuel pressure a few psi, especially if you plan on any future mods. Stoich is good for the environment, though, and your gas mileage shouldn't suffer any when you get on it!...........Peak power is seen around 12.7/1, however, with anything richer being a nice margin of safety for motors suceptable to detonation, which I don't think you are.

Nick