HI,


When traveling at a set speed and throttle position is maintained and on a flat surface..

And car is supercharged (not interested in turbo even if it is the same answer) or standard it will be running at what AFR?

13 -14? I would like to know the optimum number please or what does the car put its self to running in closed loop?

Cheers

Jamie

 

Depends if you are producing boost.

But if it's part throttle cruising then you should be closed loop.

 

I aim for 13.5 give or take a few decimal points, you still have to tune it to within a few points when you are setting up as the closed loop control on all ECUs I've worked on will only allow a slight correction in AFR before it sends them funny. ie don't just disregard part throttle tuning because you think you can rely on closed loop control to sort it out for you.

short answer 13.5ish

 

Closed loop target AFR is 14.7 for petrol.

 

13.5 is too rich should be close to 14.7 or you are simply wasting fuel. If you go up a slight hill it will get richer as it will get close to neutral or positive pressure. Watch a boost and afr gauge together and you will see they are connected.

 

Google stoichiometric ratios

 

At high rpms go a liitle richer mid 13s.

 

Those of you that tune should know that 14.7:1 is the ideal ratio chemically and not phsyically.

EDIT

I thought I should elaborate a little now I have the time, 14.7:1 is the chemically ideal burn ratio of petrol. However not all engines are capable of handling combustion at this ratio. Lucky for us ours will and on a light throttle I would be comfortable in going up to 15.5:1 NA. However the problems arise in the extra cylinder temperatures generated.

In a supercharged application that was mentioned in the original post I would hesitate to get close to stoichiometric even under light throttle applications. The reason for this is simple, the extra fuel that you are 'wasting' is keeping your cylinder temperatures down and the extra cost of fuel (which will be minute) is significantly cheaper than replacing the engine. The larger the difference between full vac AFR and full boost AFR the greater the hysteresis. This increases the risk of detonation when going from cruise to full throttle significantly even with the best engine management.

 

I don't tune but I did know that 14.7:1 is ideal for making a fuel/air bomb