Just like the title says, Does your AFR change according to outside temperatures? I ask becuz I might hit the dyno during the summer...and it gets pretty hot in so cal...sometimes 95 degrees...

Also does the AFR change from repeated dyno runs? I know whp and wtq get affected if you go back to back runs...since the engine gets heat soaked...but what about AFR? Thanks!

 

anybody know?

 

AFR should stay the same regardless of ambient air temp.

AFR on back to back dyno pulls should stay very very close.

 

nice!! thanks for the tip!

 

AFR won't change with air temperature, but power will.

 

AFR WILL and DOES change based on humidity and airtemp.
On a hotter day, your MAF reads a lower voltage, therefore lower portion on the map.

 

oh okay...thanks for the tip...anyone else wanna comment?

 

The MAF reads a lower voltage because the air is less dense on a hot day.

The MAF sensor measures the mass fowrate directly, and therefore takes air density into account. In closed loop operation, fuel will be delivered based primarily on MAF voltage and trimmed using O2 sensor information. In open loop, fuel will be delivered based on MAF voltage alone. In either case, since fuel delivery is based on the mass flowrate of air entering the engine, the afr will be independent of air temperature.

 

The MAP the ECU is using may change but the target AFR is still the same or very very close for a stock Maxima I bet. I see 14.7 in 30f-70f when crusing of idling. When I bost up my target AFR is stll the same too.

 

Same experience here.

 

The AFR is just a ratio.. so when using a MAF the ratio can be maintained easily since it's based on mass, which the MAF calculates directly without needing to know humidity or temperature. MAP is a different story of course.

Now on another note would the ECU perhaps enrichen AFR's under very high (and unusual) coolant temps (and likely retard timing also)? But I don't think the air temp is used even in that case. I'd have to check the FSM to see if it confirms those points. Can't remember off the top of my head.

 

no changes from my AFR datalogging in the winter and summer. I'd imagine if there was any, it would be a very marginal change

 

If you were running a MAP based AFR control without a Air Temp sensor or it was not properly tuned then it would.

Stock it shouldn't at all.

 

Nice...hey guys, quick question...what exactly is an air fuel ratio? Like, I know it's 13.5 to 1 ratio etc....but 13.5 what?

I also see this ratio for compression ratio...VQ35s are 10.3 to 1...what is that 10.3?

Sorry if it sounds super noobish...but the only thing I know is gear ratios....like if your 1st gear is 3.15 to 1...it means the input shaft will spin 3.15 times before the output shaft spins once

 

14.7 is the stoichiometric A/F Ratio, which is ideal.

That means 14.7 parts air to 1 part fuel. Any less air, and you're running rich, and any more air, and you'll run lean. When tuning, you'll try to get the flattest possible line, no peaks in your A/F ratio, and try to keep it the same ratio throughout the RPM range.


compression ratio is how much the air is compressed in the cylinder. When the engine goes into the compression stroke (in the 4 stroke engine cycle), the air gets compressed 10.3:1.

 

14.7:1 is stoichiometric.. yes... creates the best bang, but is far from ideal to run in a car.

Try not to get into a mind set of X.XX AFR is the best, or we need to take XX timing out.. they are nothing but numbers for easy reference.
You will find that your engine will WANT more fuel at peak torque and less in the top end.
Heaps less when the cams change over (on a variable motor)
Forget about hp, tune for TORQUE at the wheels or tractive effort if you are on a Dyno Dynamics machine.
Do short runs to say 4000rpm first.. or even deadhead static rpms to tune there... get that sorted and work on the top end. No point in pulling the car to 7k rpm if you're working at 4krpm.


BTW, o2 sensors do nothing at full throttle.. on the dyno or when tuning they should be unplugged.
Regardless fo what anyone says, mixtures will and do change with temp.. both airtemp AND water temp.
This isn't heresay, its proven facts and experience from 100's of turbocharged Nissans on the dyno ranging from 150hp atw, up to 600hp atw daily drivers. Nissans is all we do

 

can anybody vouch for Spanners? I mean, hes only got 4 posts and he just registered this month....is he legit with his sayings?

 

We not talking ideal, were talking an off the shelf nissan ecu in a basically stock car. The AFR target and result will be the same regardless of ambient air temp.

And why would I want to unplug my wideband 02 on the dyno?

 

I've got nothign to prove...
If you want to listen to my option based on experience and hands on then thats great.. if not, no probs.

I'm only here for more info on the VQ which we're going to use in our drag car.

 

In theory yes, but in practice no.
And also far from Ideal.
We typically make 20% on turbo Nissans with just an ECU change and tune.

If you're tuning a vehicle, you want the tune to as close as possible with no external influences, hence why you unplug it.