silverSS

So I got my car dynoed today on a Dynojet...

227HP/210TQ


Mods are in Signature, but my A/F ratio was roughy 14.4ish is this safe?

i was told it was very safe by the owner of the shop, I just want to make sure that I am not getting knock, and that my A/F ratio is at a safe level, Thanks!

I am planning an Injen Intake (eventually) what would this do to the A/F ratio?

Darksun

nope not really actually thats really lean. I wonder if there dyno jet was reading right. I wouldfigure with the pully your a/f's would be in the 12's but 14's I think your motor would blow intime.

MarcS

I thought a 14.x was an optimal afr?

Maybe i'm wrong.

silverSS

i thought it was optimal too

SwizzDSMSS

That is fine.

Darksun

since when is 14's optimal for a boosted aplication. 14's is alright for n/a. 10's too rich 11's safe too 12's and 13's on the agressive side 14's being too lean. If you really want to know too ask around on other site's like even a mustang cobra site or what the srt-4's run at. Bet you none of them even come close to 14's

MarcS

My last datalog gave me an average of 14.7 on my stock SS/SC under normal driving.

silverSS

So im happy as long as im keeping close to the stock A/F ratio..The cobalts run a little lean from the factory i heard..

Thanks for the input, maybe ill get some more when its not 2AM lol

Darksun

are you using a wideban o2 sensor? you know you can't use a narrow band type sensor once you add boost to the equation

BullDog71ss

14.4 is ideal. Nice numbers.

silverSS

What would a Injen CAI intake do to my A/F ratio as is?

MarcS

Injen has something called 'Mr Technology' .. I have no idea what it is, but this is what Injen says:

MRtech2
When MR Technology is implemented horsepower/torque
gains are maximized while air/fuel ratio becomes stabilized. MR Technology tunes the intake system to within SAFE FACTORY LIMITS, making it the FIRST TUNED INTAKE IN THE WORLD!

Darksun

A 'Stoichiometric' AFR has the correct amount of air and fuel to produce a chemically complete combustion event. For gasoline engines, the stoichiometric , A/F ratio is 14.7:1, which means 14.7 parts of air to one part of fuel. The stoichiometric AFR depends on fuel type-- for alcohol it is 6.4:1 and 14.5:1 for diesel.

So what is meant by a rich or lean AFR? A lower AFR number contains less air than the 14.7:1 stoichiometric AFR, therefore it is a richer mixture. Conversely, a higher AFR number contains more air and therefore it is a leaner mixture.

For Example:
15.0:1 = Lean
14.7:1 = Stoichiometric
13.0:1 = Rich

Leaner AFR results in higher temperatures as the mixture is combusted. Generally, normally-aspirated spark-ignition (SI) gasoline engines produce maximum power just slightly rich of stoichiometric. However, in practice it is kept between 12:1 and 13:1 in order to keep exhaust gas temperatures in check and to account for variances in fuel quality. This is a realistic full-load AFR on a normally-aspirated engine but can be dangerously lean with a highly-boosted engine.

Let's take a closer look. As the air-fuel mixture is ignited by the spark plug, a flame front propagates from the spark plug. The now-burning mixture raises the cylinder pressure and temperature, peaking at some point in the combustion process.



I was looking all over for some kinda proof that wasn't just some body else saying "yeah thats fine" So I pulled this off of the Garret turbo site here
http://www.turbobygarrett.com/turbob...tech102.html#e
Scroll down its closer to the bottom. So even if you think im wrong tell that to these guys. Like I said depending on if you used a wide band which you should have if your car is boosted or a narrow band which only reads right on N/A cars 14's is too lean on a boosted application. And I say again go to like an srt-4 site since there boosted or a corbra site since there supercharged and ask the same question and you will get the same answers im giving you.

ss_mike

well put 'darksun280'. i was talking with rob from hoosier performance and he was telling me that a reading like that is way to lean for our cars or any boosted car, that 11.5 to 12.5 was were we should be at or around

Doc

this is what I got http://en.wikipedia.org/wiki/Air_fuel_ratio

then I found my way to supercharges online and it says
http://www.superchargersonline.com/f...air,fuel,ratio

EndZz

Traditionally, the greatest tendency to knock was near 13.5:1 air-fuel
ratio, but was very engine specific. Modern engines, with engine management
systems, now have their maximum octane requirement near to 14.5:1. For a
given engine using gasoline, the relationship between thermal efficiency,
air-fuel ratio, and power is complex. Stoichiometric combustion ( air-fuel
ratio = 14.7:1 for a typical non-oxygenated gasoline ) is neither maximum
power - which occurs around air-fuel 12-13:1 (Rich), nor maximum thermal
efficiency - which occurs around air-fuel 16-18:1 (Lean). The air-fuel ratio
is controlled at part throttle by a closed loop system using the oxygen sensor
in the exhaust.

Darksun

so basically your agreeing with the same thing I posted before? Now look guys im not trying to throw this info back in your face like "HA" I'm right but I did feel the need to clear things up. Now as for the posters dyno sheet I'm almost postive it was done with a narrow band sensor thats the reason he got a readout in the 14's. With a pully and airbox mod the cobalt is most likly in the low to mid 12's near red line which is where I have my car right now. Almost positive if I threw a cat back on the car it would push me over. Hell when I took out my stock plugs to see how my motor was likeing the new pulley the damn things had taken a beating good thing I cought it in time and went to a step colder plug.

Darksun

Thats still based on a N/a car you have to look up for boosted applications. Think about it the air fuel read for a 2.0 N/A 4cly can't be the same for a 2.0 superchared motor when the s/c motor is forcing more air into the motor. So if a 2.0 N/A is 14.7 parts air to 1 parts fuel how can a boosted 2.0 motor at 14.7 pounds of boost which is about twice the amount of air going into the motor than its N/A counter part be safe? Same amount of fuel but twice the air. Thats called being lean. Engine temps would be through the roof. The more added fuel is what cools everything down.

Doc

Yes, I agree to it now although I was doing it the same time..it just took me a lot longer.
In no way was I trying to throw anything back at anyone. I was curious because when I was on the dyno I went to 14 then dropped down to the 10 range and I never did understand what rich/lean meant or the A/F ratio. I asked and never got an answer so I searched it and am glad I did.

Darksun

I just hope people won't be "Wrong but strong" in this situation. I tried to exsplain it in my last post why boosted cars and N/a cars can't use the same sensors for reading boost. Plus If any of them take the time and just ask on any other boosted car forum it should get cleared up quickly. But by me getting my exsample off of garrett's site that should almost be enough. I mean hell all these guys have been doing for years has been making parts for boosted applications. Just about everyone knows who garrett is and what they make so trying to say that there wrong too would be hard.

Blue04RedLine

I'm going to have to agree wit Doc and Darksun280. Hell even if I didn't it would be hard to argue otherwise. But I'm also going to add that our cars do NOT come running lean from the factory, they come running rather rich. This is the reason we can put on a smaller pully and not worry about the a/f until we get into the 2.8" size or smaller. Once we get down there, the thing that's making us run lean is the size of our injectors being too small. Get larger injectors so they aren't running at 90% duty cycle or higher, and you'll be set.

silverSS

I am going to call them and ask what kind of band sensor they used...


that should clear all this up