BLUTHUNDER

At WOT my Air / Fuel ratio is currently set at 14.7:1 .. Is this to lean ?? The reason i ask is because my headers have been getting smokin hot these days.

I'm also concerned that if my car is running to lean i may incur some detonation problems in the future.

Thanks

Jeff

flynbludream

:eek: That's very lean! No wonder you are about to melt your headers. Very dangerous to run that lean. Get it down to high 12's or low 13's and you will be better off. Be careful! :eek:

ghost.rider

In other words:

:yesnod: :lol: Y E S :lol: :yesnod:

AP

BLUTHUNDER

Why would a tuner adjust ones mixture so lean ?? Does a leaner mixture produce more HP ??
If i do re-adjust my mixture to 13.1:1 from the current 14.7:1 how will that effect my performance ?

Jeff

Redline Motorsports

That is WAY too lean!

We have found that with the "fast burn" combustion chambers of the LS engines that you can run them at 13.0-13.2:1 very safely. Of course you have to make sure your timing is also not too high. If the car where just for racing we have run them as lean as 13.5:1. Not recommended for street applications.

Most of us from the "old school" of hot rodding are used to a A/F around 12.8:1.

These engines are highly efficient. Thats why they make so much power with a good set of heads and only 346 ci!

Godspeed

The stock PCM is calibrated to adjust to 14.7:1 AFR during part throttle operation only, not WOT. This is the stoichmeteric value that is most efficient for the combusion of gasoline. However at WOT, 14.7:1 is way to lean. The best engines in the world can not survive at that AFR. LS1/LS6's make the most power around 13.0:1 at WOT and to be safe I back it off to about 12.8:1-12.9:1 - usually costing no loss of power. The trick is keeping detonation under control by setting proper timing.





[Modified by Godspeed, 5:02 PM 6/8/2002]

BLUTHUNDER

Thanks for the feedback !!
I'll talk to my tuner and suggest that he lowers my A/F mixture to low 13's.


Jeff

Redline Motorsports

Most tuners do not even get into part throttle programming. The PCM will look at throttle %, coolant temp, Mass air readings, rpm, MAP, O2 readings etc... to determine air fuel ratios at part throttle. The wide open throttle fuel and timing are fixed at whatever the stock programming is set at OR what the tuner determines.

I still think,and know, that 12.8 is too rich for best power. Low 13's!!

BLISS

Check this out, figure it out for yourself :

Redline Motorsports

Bliss,

I agree with that chart for "most" engine applications, however the more efficient the motor the leaner you can run it and more power you can make. Making 440+ at the rear wheel (safely) with 346 cubic inches would not be possible without the fast burn combustion chambers that we have to work with.

If the car where supercharged I would expect the A/F to be closer to 12.8 to keep the cylinder temperatures down.

This leaner 13.0-13.3:1 is the key to making reliable safe power with these heads. Not to mention why burn more fuel then you need to make the same power!

Terry Burger

Around 13.0 on a dynojet is ideal for the MMS head/cam packages. Are you sure you were measuring it properly?

Terry Burger

PS 14.7:1 won't damage anything but will make less power than 13.0:1 (around 5rwhp / 10rwtq I'd guess)

6Speeder

We dyno'd mine multiple runs, max power was at 13-13.5 AFR. Richer or leaner made less.

BLUTHUNDER

Terry , MMS told me that is what my A/F is set at . I"ve requested that Mike re-adjust it while its up there getting new valvesprings installed.


Jeff

Terry Burger

There must be a miscommunication as 14.7 is the target part throttle AF ratio, and 13.0 is the WOT target AF ratio.

QuickSilver2002

How do you know you are running 14.7:1 at WOT. Did you obtain this data on a wideband o2. If not, you may want to get an accurate reading before you make any assumptions. You cannot trust the onboard o2s.

BLUTHUNDER

Yes Quick , the data was from the Wideband O2 reading..It was on the dyno when the readings were adjusted.

Jeff

QuickSilver2002

Wow, that sounds really lean, and 14:7:1 on the dyno is probably something a bit higher on the street where the loads are greater.

pkmoose

As far as WOT settings, I thought the PCM was taking the data from part throttle and using that info as a base for WOT. For example, you want 14.7:1 at part throttle, if the actual reading is 14.0:1 the computer has to lean out the mixture .7:1 to get an ideal 14.7:1 (part throttle). Now, the computer uses this information to adjust for the predetermined WOT setting, say it's 13.0:1, the PCM never knows what the WOT setting is as far as a/f ratio, but takes the part throttle a/f ratio to come up with the WOT setting (meaning how much fuel to add). At WOT the PCM should not be adjusting any type of fuel delivery in relationship to a/f ratio.
As far as the original question, 14.7:1 at part throttle is perfect, at WOT it all depends on the cam, heads, headers, tuner etc... you could run 12.7:1 and as high as 13.4:1.