Air/Fuel Ratio Understanding for Tuning

[Nachius]

Ok I want to tune my car and don't really know where to start with the air fuel stuff.

Basically we have O2 sensors giving us mv readings like .9

and you want to end up with an actual air/fuel ratio of like 12:1

basically I want to know what is ideal for N/A and Nitrous and how do I convert my O2 readings to an acutal air/fuel ratio.

Once I have that part to install larger injectors I would have to edit this once again

basically would this be a across the board percentage change and how would I figure each of say going from stock 22# to 24#, 28#, 30# injectors?

I know I'm going to need bigger injectors and I want to completely understand before I install them what exactly I need to edit and what number I want to be close to.

Thanks, Shane

[94TeaL]

Ideal is like 14:1 but 12 is pretty good. Better than 10:8 like me.

[Nachius]

Originally posted by 94TeaL:
Ideal is like 14:1 but 12 is pretty good. Better than 10:8 like me.

doing a little research seems like I want 14.7:1 A/F or close to .82 O2 readings.

Again how do you figure up A/F from your O2 readings? [img]smile.gif[/img]

Is it better to tune of Long Term Fuel Trims than it is from the O2s and if so what do I need to look for there?

[ July 21, 2004, 05:19 PM: Message edited by: Nachius ]

[AllTheGoodNamesAreGone]

wow.. ok you all..

there are alot of theorys on this.. however speeking "generaly"

the idea stoich AF for a car that is jsut crusing around is like 14.1 or something..

at WOT... you want to be around 12.7 for an NA car..

and 11's for a FI car..

now.. keep in mind.. those are jsut "rules of thumb" if anything they are good starting points..

adjsut from there..

[speedy-v6-camaro]

There are many websites that will help you figure all of this out. Search yahoo and you will come up with some.

[Nachius]

Links? ;)

[John_D.]

It's difficult to give exact numbers with narrowband sensors. They are very accurate just to either side of stoich, and less accurate at the ends of the ranges.

And as they heat up (like from the start of a wot run to the end of it) they read differently too...

I seemed to run strongest around .88 na and around .93 nitrous. You can check your times against some different readings and see which ones tend to work best for you.

It's difficult to find any good "volts = a/f ratio" information. I have 3 graphs on my pc at home, but don't have the links handy where I originally got them. One problem is that going from .920 to .925 could be a big difference in a/f from 12.1 to 11.8 (just as an example) -- a big a/f difference in a small o2 voltage change.

What are you going to be using for tuning?

Bigger injectors, if you want a decent idle, will require a full featured tool like hptuners. You can get by with 24's with something like a maft or mini-afc.

[Nachius]

I am using HPtuner software and have started with the basics already.

I am going up to 30# injectors for a larger dry nitrous shot, and in the near future heads, cam, pistons, whole engine basically, and an even larger shot, approx 150 dry shot.......

I want to make sure my air/fuel, timing, knock is all good with my tunes for nitrous basically.

[John_D.]

I ran a 150 shot on 24's...

But that was without heads, cam, etc which would have required even more fuel.

Have you upgraded your fuel pump yet? I ran out of pump at a 120 shot.

Fuel pressure gauge might be a good "tuning" tool to invest in too. You could end up chasing a low a/f ratio with injectors, hptuners, etc when the fuel delivery is the problem...

[Nachius]

Yea I have a walbro 255 in tank, and thats the only gauge I plan on running in conjunction with HPtuner monitoring is the Fuel Pressure Gauge.

I figure with heads/cam/forged pistons, and 150 shot 28# would probably be sufficient, but if I can tune it I decided to go with 30's just in case.

[Just Another V6]

<~~~Spraying a 150 Wet shot and is running rich...

O2 Simms help alot!

[Turbo V6 Camaro]

umm from my reading

NA/cars make best power at a 12.5:1 , car are tuned for a 14:1 becuase it lowers polution and passes the states pol tests

factory O2 are only acurate at 14:1 ratio the more you vary from that the more they are off.

FI cars should am for a 11.5:1 ratio b/c of all the extra air in there your gonna need more fuel

[Turbo V6 Camaro]

Originally posted by Just Another V6:
<~~~Spraying a 150 Wet shot and is running rich...

O2 Simms help alot!

i bet .25 your injectors are locking up and at 100% duty cycle

[Just Another V6]

Originally posted by viper04af:
</font><blockquote>quote:</font><hr />Originally posted by Just Another V6:
&lt;~~~Spraying a 150 Wet shot and is running rich...

O2 Simms help alot!

i bet .25 your injectors are locking up and at 100% duty cycle </font>[/QUOTE]So you think that they are staying open at WOT and flooding the heads?

[Turbo V6 Camaro]

yeah the computer sees all this air coming in and it can get any fuel so it does all it can and just holds them open to get as much fuel in there before the intake shuts, hell it might not even stop spraying the injector let fuel biuld up so it there when the intake vavle opens