I have been told that the air fuel ratio should be 10.5 at the exhaust system, is that right? I am going to have it tuned on a dyno.

Thanks!

 

Depends on what boost you wanna run....Also what fuel...pump gas,,,race gas.....
10psi i'm at 12.0 fuel ratio...higher you go the richer you want A/F RATIO...

 

10.5 is very rich. 14.6 is ideal but like "street" said, you will want to run a richer A/F with higher levels of boost to keep from running a lean condition and popping the motor.

What car do you have? Mods? PSI if turbo? Answers to these questions will help you get your answer.

 

richer for more boost will not help power or reliability or the safety margin. 11:1 is a good round number to go for, it has a decent safety margin and will only generally lose a few HP vs leaning it out more to try and squeeze the most out of the AFRs.

keep in mind AFRs are meaningless if you start pushing too much boost or timing is severely off and internal temps soar, detonation is your enemy.

 

+1

 

14.6 is ideal for reducing emissions. That's where that number comes from, and that's why a factory ECU on just about any car will try to keep it at that AFR when possible.

 

Just some FYI: You might see 13 to one at idle, but if you reconnect the airpump, ACV and have it working properly, that figure will turn into a 14-15 to one figure. That's prior to the catalytic converter and it's assumed that the catalytic converter will clean up the emissions better with that ratio.

If you have full emissions on the car and are looking at the afr on a gauge, then pull the BLUE connector off the Relief solenoid, you should see the afr plummet because now the airpump air isn't going to the exaust ports but is NOW being dumped overboard.

 

how much will a/f ratios change if you are using a inline sensor ( pluged into the exhaust somewhere ) or using a rear muffler sensor, you know the ones they clip ontop your tip and it sticks up inside the pipe a bit.
note this is for use on a dyno and the car will not be moving anywhere

 

As long as there is no catalytic converter and no air leaks at the flanges/pipes, then the afr should stay the same. At one time I had a wideband located just before the left rear muffler and it read the same as when it was a foot or two from the turbo.

I've never run one with it just stuck up the tail pipe.

 

when I took my GTU to the dyno, my onboard wideband read a full point of AFR richer than the tailpipe wideband (so mine said 13.5:1 and his said 14.5), but those tailpipe widebands are calibrated, so it's going to vary.

My onboard wideband O2 is mounted exactly 36" from the exhaust port per AEM instructions.