2 replies to this topic

[topcat]

Hi, Just wondering about A/F ratios in different conditions. Is 17:1 OK for cruise? and 13.5:1 for full throttle? (on a 1990 cooper carb HIF44) Any more info on this topic would be useful, thanks

[Dan]

Oh dear you've got one of those air/fuel meters haven't you? Remember that the point on the gauge that it says if OK is the stochiometric ratio which is what you need to run to keep a cat healthy. It's actually appallingly inefficient in terms of fuel use to run a car at the stoch ratio if you don't have to (part of the big con that catalysts help the environment) and you can run a lot lower than that, still develop the same power and not see any engine damage.

Ignore the gauge for the time being, get it set up on a good rolling road (one where they know what they're doing instead of stting it up using a fuel ratio gauge as if it had a cat) and then after it's set up properly see what the gauge says. That's what you should be aiming to keep it at in future.

[topcat]

Yer i have, its quite interesting, it didnt work very well for a long time, works well now since i put another earth strap on. had a bad earth strap and the lambda sensor earths through the engine earth strap.

I dont have a cat in anymore, ditched that a long time ago.

Good advice getting it on a r/r i know but money is a bit rare at the mo. (students!) I played around with borrowed needles for a while over the winter untill i settled with a bbw, could still feel it was a bit lean on the motorway so spent some time just taking a touch off the needle until it felt good. To be honest it goes really well now, the gauge gives good readings but I know its not good enough tune a car to accurately. I have also colourtuned for idle. below is the chart for the gauge readings, it says its just to be used for full throttle but gives a resonable reading for cruise aswell. (around 0.040 mv average - it used to give minus readings!)

 chart.JPG   36.11K   5 downloads

I guess what i'm getting at is whether i'm damaging my engine, at the end of the day if it doesnt feel lean to drive, it goes well, it doesnt overheat, and i dont get soot on the exhaust or on the plugs it cant be too bad can it until i eventually get it on a rolling road?

Edited by topcat, 02 August 2006 - 11:46 AM.