Whats the best boost AFR

[Holden202T]

Ok so as the topic says, im interested to know peoples experience and thoughts on boost AFR tables.

i've done a bit of research and i can't really find any definative answers or rules, other than keep afr's between about 12-11.5 for boost.

so that side of it i'm fairly well happy with, BUT the question i can't seem to answer is this:

if you are tuning a 2 bar tune and can define boost AFR every 10kpa from 100-200 do you start with 100kpa (N/A numbers) and then blend them from there to 11.5 as your boost increases, or do you go, ok we are in boost so flat table of 11.5 for any boosted cell.

now i can understand theories like running richer for cooling and such, but i am more interested in knowing if other than cooling a turbo etc, is going anything richer than say 12 just pouring fuel out the back etc.

basically i want to know what is the right way to setup the AFR table if there is one or if nothing else get everyones thoughts in one place because it seems all the info on the net is all over the place!

[VX L67 Getrag]

I.M.O. only depends on how long your foot is going on the GO pedal, if it's track driven going to be sustained & need quenching, street driven & can't go too long on go pedal without being caught I've found best power & all round response & drive-ability around 12!

[Holden202T]

ok so if you go for 12, thats obviously safe enough, but the only issue is your going to get everything hot whereas if you went richer like 11.5 it will keep things cooler for sustained bursts, ie. circuit car ?

[The1]

11.7AFR is pretty much the accepted industry standard for boosted on PULP. Much like 12.8 is for N/A, Most tend to just set fuel at that, then tune max spark.

Typically it operates on a Bell Curve, 11.7 in the middle, obtain good all round spark,power,safety and economy.
On the lean side get a little more power, save some fuel, risk of retard or knock, hotter burn temps.
On the Rich Side get a little more power, get a degree or two more spark, less chance of knock, cooler burn temps, but use alot more fuel.

Ideally some way of measuring internal cylinder pressure would find max power/torque. I have heard that some head gasket manufacturers are able to integrate pressure sensors into the gasket so this can be measured, ive not seen one for real though.

For a track car your prob not worried about fuel, so tune between 11.5 - 11.7

I have had a few dyno tuners tell me that you can get slightly more power from going lean than rich. At the end of the day there's prob not much in it.

[sparx-1]

Totally depends on your set up, If it's all going south ie too lean AFR. your egt temps will be a good indicator. Auber sell a reasonably priced egt temp gauge, just buy a good probe to go with it and you will have a good heads up before you melt those engine bits apart from some dyno time that shows a kw/hp output while you lean out the AFR in each cell till it looses power and then fatten it up a tuch for safety i reacon it's has to be the next best thing for us home tuners.

[Holden202T]

ok so most people seem to be fairly settled on 12-11.5 afr's but what about as boost increases, do we have a flat 11.5 across the board or blend from 100kpa afr's into 11.5 at max boost ?

[The1]

anything that doesn't class as normal low load driving, say over 30% tps.

Also there should be a power gain switching to PE even without any other changes, because load has increased so more power can be measured. This is different between cars/engines/gearboxs etc as load points vary.

[VX L67 Getrag]

Well when I tune FI cars on the dyno I tune timing for peak torque/power with it at 11.8 & then try 0.5 either side of it for better curve, but generally works out 12.0 is best so long as not too much boost & not too much timing!
There’s a lot of PE modifiers when on the Dyno I NULL them all & then once done on Dyno I reset back the modifiers to stock as GM didn’t spend all their time sorting that out for no reason!

[Holden202T]

thats not what i was asking, i am meaning would you use the target AFR as 11.5 from 110kpa to 200kpa or would you slowing richen it from 100-200kpa ??

happy to provide 2 tables showing what i mean if that helps ?

[VX L67 Getrag]

Ahh Right, I get what you mean I'm guessing once you log it at that change over point you'll be getting to higher TPS setting & changing over around there anyway, but if you have the option than hell yeah why not make it 12.8 below 100Kpa & 12.2 at 120, 12 @ 150, 11.7 @ 180 etc...