FriedDumplings

Whats up, can someone share w/ me what is the correct air/fuel ratio to the amount of boost? What is the formula? Thanks,


Joe

FriedDumplings

I did read about the wideband wired o2 senor gauges and regular A/F gauges but I'm kinda confused on how to read the gauges. I see the gauges go from like 10-17 but what is it actually reading? Help a noob please.

yuichiror

iTrader: (1)

I'm sorry I can't answer your question, but I just wanted to say that I love the .gif! My kids are huge MM and Minimoni fans.

DCrosby

Well the short answer is no higher than 11.5-12 above 0 Manifold Pressure all the way to maximum boost.

The long answer is you need to worry about Inj. Duty Cycle, Oct/Ron (Gas) Rating, Spark, and IC Core Size...

The really long answer is read an electronic fuel injection self help manual... or a Haltech or any other aftermarket fuel computers manual... AFR is AIR FUEL Ratio, and at 14.7 i belive is what's called Soitch, or optimal burning of fuel and air, anything higher is more air than fuel, and is Lean, anything lower is more fuel than air, and is rich. Now Piston cars can Idle at stoich, I've yet to see or be able to idle my Rotary @ stoich, most of the stable idles are around 12.9-13.5 for a rotary. It's nomal for a rotary to lean out to 17-18-19 and above during deceleration, since you're starving the motor of air, and consequently fuel to slow it down... but any other time, it's mostly going to run rich... or 14.7 and below... now under boost you're hating everything up including the intake air, and to cool it down you need a good Intercooler, and most likely some extra fuel to keep the whole mess from exploding prematurely.. or above TDC (Top dead center)....

If this is way above you and you have no clue on what I just said, you're going to learn a couple of hard lesons, one a Wideband is woth every penny, and having a tuner who knows what he's doing to come out or fly out at your expense is far cheaper than blowing a motor.... and that book can really help if you don't have option two....

P.S. Some people run 10.5 -11 AFR under boost to give themselves some safety... and it's not like your AFR curve is going to be all level when you tune anyhow...

-DC

sonix7

DC that was awesome. I have read about it but, that was a great explaination. I have a UEGO WB 02 and a PFC with a MED SMIC. I am trying to learn as much as possible so I know what the tuner is doing and maybe one day pick it up slowly. Thanx

FriedDumplings

Thanks DCrosby, I get what your saying in your response. You know when I look at A/F gauges some of them only go from Rich-Soitch-Lean and doesn't really show increments of lets say .5 to really know what readings your getting. How do you get an accurate reading w/ a such a vague gauge like that? Or, can you only get an accurate reading from a wideband reading?

Bad2ndgen

You cannot get an accurate reading with the cheap gauges for a few reasons... First the guage does not have the resolution you need when tuning a car and second and more importantly the gauges are reading from a narrow band 0-1 volt sensor wich is only accurate very close to stoichiometric or 14.7:1 AFR. A wide band on the other hand has a linear 0-5v output thet can accuratly sweep from around 9.0:1 to 30:1 giving you an accurate air to fuel mixture reading.

On to the tricky stuff and your first question... The air/fuel raito is just as it says, how many parts air to how many parts fuel by weight so 14.7 parts air to 1 part fuel is stoich in standard gas or the most perfect cumbution possible leaving behind the least bad deposites of harmful gasses. You can make cumbustion with much less fuel but you will be losing power because of lack of cumbustion energy. Now for the bad news or good news for us tuners...

There is no formula for finding the correct A/F mixture under load. Every engine is differant in what it needs to be happy depending on a multitude of factors. However I can help dispell a few miths that are widly taken as gospel. Number 1: Fuel has almost nothing to do with how much power an engine will make... Beyond a 14.7:1 AFR fuel is simply thermal control, trying to keep the heat inside the combustion chambers at acceptible levels where preignition or detonation will not take place. number 2: There is such a thing as too rich and this can also lead to detonation and is very common when using higher octane racing fuels without changing your timing accordingly. number 3: racing fuels will not add power nor do they burn faster, they accually burn slower and are harder to combust and that is why they don't preignite as easily.

Ok Im sick of typing and am getting a little off topic but the moral of the story is educate yourself before attemting to tune your own engine and I don't mean sit on the forums and read what every 16 year old kids opinion on tuning is. There are places where you can learn the facts on how engine tuning really works and it is not black voodoo magic.


www.efi101.com

Regards
Justin
www.alienauto.com

clavier

That's not quite right.

Because of the speed and complexity of the flame front, the mix must be a little rich to ensure that maximum combustion actually takes place - somewhere in the 13.5:1 range.
Though it is true that the leftover fuel isn't actually making power, there would be air in the chamber that doesn't get exposed to enough fuel at all without it.

Also, the thermal value of the fuel is a bit overstated. Lots of fuel does little to quell combustion temps directly. It tends to simply extinguish combustion to some extent which is not the same thing.
The heat absobtion capabilites of fuel are actually pretty lousy. Water is better if you really want to go that route (which I personally don't recommend).

Bad2ndgen

Agreed...

Justin