air fuel ratio

[GTP091]

What's the min, max, and normal air fuel ratio for a 91 DOHC?? I'm looking at getting an analog air/fuel gauge and want to make sure I get it in the right range.

[robertisaar]

for cruise, it's abviously going to stick around 14.7:1, but for a N/A motor at WOT, i like to keep it near 12.5:1.

turbo/CSC: around 11.5:1

roots: 10.5-11:1

it's a safe place to start, and you may gain some power by leaning it out.

[RedZMonte]

make sure you get a Wide Band A/F Gauge. the ones that piggy back off the stock O2 sensor don't really do much for you. I have a AEM WBO2 in mine, works great. I have a little tuning to do on my partial throttle light acceloration ratios, she runs a little fat at partial throttle as well as off throttle decel. over 3K Rpms.

Crusing: ~14.5:1
WOT: ~11:1-11.5:1


Are you tuning it somehow? What mods are done? the Stock computer is going to command thoes same ratio's (approx.).

[GTP091]

make sure you get a Wide Band A/F Gauge. the ones that piggy back off the stock O2 sensor don't really do much for you. I have a AEM WBO2 in mine, works great. I have a little tuning to do on my partial throttle light acceloration ratios, she runs a little fat at partial throttle as well as off throttle decel. over 3K Rpms.

Crusing: ~14.5:1
WOT: ~11:1-11.5:1


Are you tuning it somehow? What mods are done? the Stock computer is going to command thoes same ratio's (approx.).

I'm just gathering info and items I need to add a turbo later on. No tuning as yet mostly still stock. I was under the impression a wideband o2 sensor is only needed for use on OBD2 vehicles. If a narrow 1 wire band can effectively read the air/fuel ratio isn't that the point or is a wide band used because it is able to read changes faster and thus considered more accurate? I'm at a position where it would be stupid for me to have the turbo system worth more than my car but I like my car and have to much invested to buy a newer sporty car. So I will be using a FMU and other non respected methods to get it turbo'd. Just for fun; these aren't race cars. I'm looking at Koso gauges; they are analog so match stock closer than all the rice looking brands. What do you think??

[robertisaar]

wide bands don't care what computer setup you're running. and i can personally tell you that a narrowband has a response time of far less than 1/10th of a second. good enough for you? but that's not the reason that WBs are more accurate. it's due to a more linear output voltage.

but a narrowband can't really tune the WOT needed for boosted motors. they do fine with n/a setups, but boosted AFRs need a wideband.

[Azrael]

Narrowband O2 sensors will tell you 3 things: lean, stoich, and rich. No more than that and nothing in between. Widebands will tell you exactly where you are between 10:1 to 20:1 afr's.

[robertisaar]

to a point, that is correct. when at WOT, however, a narrowband is more useful than people would like to admit.

using a heated NB O2, WOT on a N/A motor is fine.

[RedZMonte]

for tuning purposes NB o2 gauges are vertually useless... better to spend your money on a few base line dyno runs (~$30-$50) and have them use the WBO2 on the dyno. I ran a FMU and 5psi for a few years with good luck. anything over that you really need to do injectors and some sort of tuning.

S

[ForcedFirebird]

Umm, all the boosted motors I know of, and have worked on, we still use 12.5:1 in PE - although I will agree with robert on the fact that rich is safe so start there.

Wideband CAN be used, but I will tell you ALL of the guys that think like robert does and thought they were fine using the NB for tuning completely changed thier mind after using a wideband

I would also like to add that the best scenario is to use the NB to feed the ECM, and use the WB to log and guage. Even though most WB's have a pair (or three) programable outputs, the ECM will not like the simulated NB out. A NB will read more like a sine wave when you graph out the voltage whereas the WB will look more like steps/line and will take quite a bit of playing with the curve to get good results (not worth it in my opinion).

[timg]

Agreed. Narrowband AFR gauges are light shows and nothing more. I had one for a long time. It went rich at WOT (usually), bounced at idle and cruise, and lean on decel. It had virtually no tuning value whatsoever. Widebands cost more, but it's worth it to have an actual tuning tool. Narrowbands are designed to keep cars stoichiometric for emissions purposes: no more and no less. They are NOT a tuning tool unless your goal is to run stoichiometric all of the time.

Tim