Ideal Afr For When On Boost

[Mad Professor 7]

Hi All.

 

Does anyone know what is the idear AFR for when on boost?

 

ATM this is how I have got my AFR setup.

 

Thanks for your time.

[petert 554]

The further you move away from atmoshpheric pressure, the richer it needs to be.

 

ie

 

full throttle 0 kPa - 12.5:1 (the same as a N/A engine)

50 kPa boost - <12:1

100 kPa boost - 11.5:1

 

 

I wouldn't go anywhere near 12:1 under boost unless you've got a very experienced dyno operator/tuner. The combination of a lean mixture and incorrect ignition timing will result in instant destruction. Many turbo cars run very rich mixtures (between 10 and 11:1) as a safety net.

[Mandic 0]

Sure if one runs too rich mixture the fuel can wipe off the oil from cylinder walls?

 

 

Cheers

 

Ziga

Edited January 15, 2006 by Mandic

[DrSeuss 0]

The main purpose is to cool the pistons and combustion chamber. Making the charge more dense and mainly to help prevent detonation. As detonation will kill an engine in seconds, bore wash takes a few hundred miles.

[Mandic 0]

Agree with You about the cooling purposes, but still, I wouldn't say bore wash takes few hundred miles + that extra fuel goes into sump and mixes with oil (not good for lubrication).

 

I'm not saying rich mixture is bad, just asking how much effect does too rich (ie. <12.6) mixture have.

 

 

Cheers

 

Ziga

[Guest andy309goodwood]

interesting

i would have thought that you would want to be aiming for a slightly richer mixture the higher up the rev and boost range

would be very interested to hear the progress of this one

[DrSeuss 0]

After discussing tuning it would appear one of the main reasons is turbo's simply don't manage to burn all the charge. So some of it just goes out the exhaust as unburnt fuel. This also accounts for the somewhat poor fuel consumption you will see on a turbo'ed engine (for any given power)