The V8 Owners Forum -

What should be ideal afr ratio please? Whilst its sat ticking over and the lc-1 is plugged into laptop its showing high readings (18) but this does drop when throttle is pressed, I'm going to test drive tomorrow to get true readings on boost etc when engines warm.

Hi
Idle around 15:1 maybe 15.5:1 but really whatever gives you a stable idle without hunting. As long as when boost comes it goes to about 12.5:1 then at Idle you want it as lean as it will go and still be stable. If it is draw through then the atomisation and mixing should be very good so it should be able to burn nice and clean and not build up carbon deposits.
Best regards
Mike

I would like to see under boost AFR around 11.5 to 12.0 and no higher.

Idle doesn't really matter as long as it is not smoking.

Thanks
Clint

I can't get my 4.6 lump anyway near 15:1 at idle, it has a reasonably hot cam and very free flowing exhausts which probably don't help. (Neither does the Eddy carb!). Anyway it's fine at 12.2:1 and goes rough if I lean it off to 12.5:1

I don't have any turbos to mix the air and fuel up either! Dunno why I posted really!

Factory spec idle on a Vitesse is approx 14.1:1, if that helps.

I'd be very surprised if you had a stable idle at 15 or leaner.

Idle, anywhere between say 13.5-15.0:1 would be acceptable. 13.5 may not pass MOT or be borderline, but it would be a good strong idle mixture

On boost. Many variables, ie boost, compression, intercooling etc etc.

12.0-12.5:1 may be fine on a low boost application running nowhere near knock/detonation. It absolutely would not be fine running more boost or with higher charge temps etc.

11.0-11.5:1 is a fairly generic safe target for most builds whilst on boost.

No way would my dakar idle at 15:1 - needs around 13:1

Mine is most happy with AFR at 12.8 - 12.5 at idle. 11.5 at full pedal.

sidecar wrote:I can't get my 4.6 lump anyway near 15:1 at idle, it has a reasonably hot cam and very free flowing exhausts which probably don't help. (Neither does the Eddy carb!). Anyway it's fine at 12.2:1 and goes rough if I lean it off to 12.5:1

I don't have any turbos to mix the air and fuel up either! Dunno why I posted really!

Smaller 4.0 with lairy cam and minor mods wont idle smoothly unless at 13.5 or richer, any leaner and it runs like poop and makes the cam sound splashier than it is splashier! is that a word?

SimpleSimon wrote:

sidecar wrote:I can't get my 4.6 lump anyway near 15:1 at idle, it has a reasonably hot cam and very free flowing exhausts which probably don't help. (Neither does the Eddy carb!). Anyway it's fine at 12.2:1 and goes rough if I lean it off to 12.5:1

I don't have any turbos to mix the air and fuel up either! Dunno why I posted really!

Smaller 4.0 with lairy cam and minor mods wont idle smoothly unless at 13.5 or richer, any leaner and it runs like poop and makes the cam sound splashier than it is splashier! is that a word?

I bet your Mega squirt is allowing you to run it leaner than if a carb was fitted. For example I can not run my cruise any leaner than 15:1 but I know of engines with squirters that will go much leaner, oh well I still like my carb!

Er you don't live in or near Wokingham do you?