Air / Fuel ratio question

[Justin]

What is the safe operating range before I know I am running lean?

 

My Dyno chart goes from 14.79 AFR at 2051 rpm down to 11.12 AFR at 4500 rpm then up to 11.90 AFR at 6000 rpm.

 

What is a dangerous AFR level to look out for please?

 

Thanks

 

Justin

[Adam W]

You want to aim for somewhere near 11:1 under boost, 12:1 is too lean for safety and 10:1 is too rich for max power. When you're off the boost the car will sort itself out and aim for around 14.7:1

[Justin]

So after 4500 rpm the lines should stay down at the 11.1 area and not go up past the 12 mark like they have here on my dyno chart is that right?

[Guest Terry S]

No it depends on the throttle position. You could still be cruising at 4500 rpm, just like you could be booting it below 3k. It is mapped according to the load.

[Adam W]

But if it was a full-throttle run then yes, that does sound too lean to me. What are your EGT's like?

 

Edit - just read your EGT fitting thread 12.15 probably isn't "instant engine death" territory, but it's usual for cars to run a bit leaner on the road than they do on the dyno from what I've read. This is why people try and aim for a conservative 11 or 11.5 max. Seek specialist advice from someone who knows about it, rather than has just read about it like me

[Justin]

So would it do any good/harm putting a Walbro and an FSE on to er on the safe side or do I need to look at bigger injectors etc?

 

Cheers Tel and Ad for your time.

[Adam W]

It depends whether you're running out of fuel pressure at the top end or if your injectors are maxed out (ie >90% duty cycle). There are threads on here about when the standard pump runs out of juice, can't remember eactly when an upgrade is recommended. An FSE won't do any good if the problem is your fuel pressure dropping off due to the pump being weak.