A/F Ratio under boost and WOT

[GSX1300R-T]

Hey Guys,.........what A/F ratio are you looking for at WOT under boosted conditions. My research says between 11.5 and 12 to 1. Those of you using wide band systems,........what numbers are you using? Those of you that have blown engines,........any idea how lean the fuel system was at the time of failure? I'm building a DIY system and trying to finish my research with the fuel mapping. Thanks for any help! I've been reading the message boards for a while,.......and I'm very impressed with some of the DIY guys on here. Keep up the great work!!!!

 

[reaper0995]

11.5 to 12.1 or so is my goal. (DIY here as well)


keep us posted and post some pics of the build when you get there

 

[Uncle Bob]

I aim for 12-12.5:1, but with carbs, its a compromise....usually have a lean spike coming on to boost.

Not like that really adds much to this....but its what I aim for

too much fuel just loses hp. If you need that much fuel to make it safe, you're running too much boost IMO

 

[hawkwind racing]

I use Lambda instead of A/F ratios ,for several reasons ,best power is lambda 0.85 /0.9 I believe best MPH is a bit leaner
anyway what lambda / AFR meters you blokes using ?
gary

 

[TurboProstreet]

Quote "I use Lambda instead of A/F ratios ,for several reasons ,best power is lambda 0.85 /0.9 I believe best MPH is a bit leaner"


So whats the difference between 0.85 Lambda and 12.495 A/F?? Or the difference between 0.9 Lambda and 13.23 A/F??
If you run .9 lambda with a turbo you will get best mph.....once!


-

 

[Gary Evans]

(TurboProstreet @ Oct. 19 2006,06:57) Quote
So whats the difference between 0.85 Lambda and 12.495 A/F?? Or the difference between 0.9 Lambda and 13.23 A/F??

Depends upon the type of fuel used. The advantage of using Lambda values is that the relationship stays constant regardless of fuel type. If your only using gasoline A/F is easier for most to relate.

 

[Uncle Bob]

bah. 13.2 isn't "instant death" unless you're on the extreme edge (with cast pistons).

cast pistons are very unforgiving. If you want to play with fire, use forged pistons. thats one of the reasons I get away with 18psi on pump gas

 

[TurboProstreet]

I didn't say instant death, but it is a 90% chance that if you go out and play with 13.2-1 on pump gas your going to eat a piston or at least push out the head gasket. Seen it way to many times allready. And you would be surprised at how good the Busa forgings actually are. But it all comes down to if you have a poor tuneup then bye bye so use some kind of wideband or the dyno and tune them right, no guessing or using somebody elses map and calling it a day without varifying it.

-

 

[smithabusa]

I have made 460 hp with stock pistons, they don't see anywhere near that abuse on the street, but have been up to 22 psi a few times in the upper gears.

 

[GSX1300R-T]

(smithabusa @ Oct. 20 2006,12:25) I have made 460 hp with stock pistons, they don't see anywhere near that abuse on the street, but have been up to 22 psi a few times in the upper gears.

460 hp is pretty stout for stock pistons. What A/F ratio are you running under boost? Thanks for any input.

 

[Uncle Bob]

22 psi on race gas is a whole nother deal.

What kills any piston is detonation. Using high octane gas will reduce the possibility of detonation.

As for strength of the piston....yes, cast pistons can be used, for 1000's of miles of trouble free use. But you have that one time where things go bad (such as running out of gas while under full boost) and its very possible the pistons will be done.

Forged pistons are much more forgiving. It takes more than one single accident of that nature....most of the time

And I'm quite sure that running 13.2:1 AFR with 2 psi wouldn't cause any issues....its all about the state of tune, as I said. Closer to the edge you are, the less forgiving it is.