what's a safe afr to run the car under full throttle? i just got a more aggressive street tune today, i know the leaner the car runs the more power it makes. my afr used to be 10.6-10.9 under full throttle, it was dyno tuned by Turbotrix. after the street tune today my afr is 11.1-11.4 under full throttle. is that too lean? oh im boosting 24psi on 93 octane

 

uh? any thoughts?

 

Thats a safe AFR if you want to see if its too aggressive you need to datalog for knock count.

 

so whats considered rich or lean?

 

New to this i see.

14.7 is considered stoichiometric meaning perfect A/F ratio for the best Burn

Turbo cars run richer becuase as you increase pressure this thing called "knock" or pre-detonation occurs. This is bad causes damage to the engine and so forth. Generally you will see afr's on turbos around 11 or lower for safety against knock and aggressive timing.

There are quite a few threads on how to tune and afr's and so forth. Just look for them via search.

 

your a/f ratio is fine by itself, but that's a lot of boost for 93 octane.

 

not for a well tuned 9

 

i agree...but i wouldnt run that everyday... i only run 22.5 to 23 ... and that is pretty agressive i think... also it gives way to spiking occurences for safety

 

Try waiting more than 14 minutes next time.

11:1 is what I (and many others) have found to be the best compromise on pump gas. Going richer than this doesn't often do much to reduce knock, while removing just one degree of timing can get rid of 2-4 degrees of knock retard. Going leaner than 11:1 will slowly add a little bit of power, but the knock starts to go up exponentially. So 11:1 seems to provide the best compromise.

On race gas I run between 12:1 and 12.5:1. NA cars usually make the most power just under 13:1. Even with race gas we tend to still run a little richer to fight knock. It's all about comromise, and doing some testing to see what works best on your setup for a given fuel.

It's also a well documented fact that more boost makes more power, even if you have to go a little richer and pull out a degree or two of timing. It's all about airflow. Timing also has a significant effect on power, but you quickly reach the point of diminishing return, and you have to watch out for that. With AFR in the "normal" range, I don't see significant changes in HP when testing with it. These are my personal observations from the tuning I have done on DSMs and my EVO, YMMV.

 

Talking of AFR, I have an AFR graph of my car, can someone have a look and tell me if it looks right or out of tune etc?

I'm no tuner so no need for flaming.

 

If this is pump gas, 11.8 up top is a little leaner than I would be comfortable with. It looks like it's also too lean when airflow/rev peaks, but without the torque curve it's impossible to be sure.

 

hmmm I don't have the torque curve and it is running on pump gas. My tuner did say that it was struggling to get more fuel through. I have since upgrade the fuel pump, but haven't been back onto the dyno yet.

 

If the EVO 9 pump is the same as the 8, that'll do it. I just posted some onfo about this in the when to upgrade fuel system thread in this section. Depending on how that dyno reads, using the typical DD fudge factor of ~17% puts you right at the limits of the stock EVO8 pump, roughly of course. If you get back on the dyno, it will be interesting to see if the problem was in the tuning or in the pump.

 

I got my hands on the torque curve, mine is the lower green line.

 

Yeah, that's pretty lean during peak cylinder pressure. It takes way too long to get AFR down to where it should be. On my car I like my AFR to be very close to my target AFR as soon as it hits peak torque. You're still around 12.5:1, I'd rather see mid 11s at the most.