air fuel ratio not actually 14.7:1?

[bcjammerx]

So I was reading on wiki about air/fuel ratios, and it was saying how the "test fuel" consisted of

n-heptane and iso-octane

but that our fuel has

combination of heptane, octane, a handful of other alkanes, plus additives including detergents, and possibly oxygenators such as MTBE (methyl tert-butyl ether) or ethanol/methanol

which apparently can push the ratio down...i.e 14.1:1 This is a more rich mixture yes?

So what does this matter in terms of tunning be it n/a or boost? Is that a small change from 14.7 to 14.1? How can you find the ratio for the fuel you run or should you just go with 14.7...or 14.1 :1 for your a/f ratio?

Granted it doesn't specify octane rating really

Does this mean on an n/a build I should shoot for 14.1:1 a/f ratio?

or *see below

also from wiki

In Naturally Aspirated engines powered by octane, maximum power is frequently reached at AFRs ranging from 12.5 - 13.3:1

true? how dangerous is this? Is this meaning 100 octane rating? Seems to make the argument of what IS the true stoich. ratio null

[chessboxer]

You only want an afr of 14.7:1 when the car is at idle essentially. Under load, it varies, but you generally never want to see over 12.5:1

A lot of tuners will shoot for an afr under load of around 11.5-12.0 on a dyno and then at peak torque bringing the afr to around 12.5

This varies per application, engine cr, egt, etc, but it serves as a decent guideline. Cars often lean out a little on the street after a dyno tune, so shooting for around 11.5-11.7 usually brings it up to around 12 on the street.

[keycb7]

You only want an afr of 14.7:1 when the car is at idle essentially. Under load, it varies, but you generally never want to see over 12.5:1

A lot of tuners will shoot for an afr under load of around 11.5-12.0 on a dyno and then at peak torque bringing the afr to around 12.5

This varies per application, engine cr, egt, etc, but it serves as a decent guideline. Cars often lean out a little on the street after a dyno tune, so shooting for around 11.5-11.7 usually brings it up to around 12 on the street.

^^^that would be under boost application, and 12.8 AFR best power for N/A (if I remember right)

Octane rating would be tuned more by timing and not so much by AFR's
Also other fuels needs less oxygen to burn then others.

[93F22A6]

12.5:1 AFR according to gale banks for best performance and 14.7:1 for best fuel economy.

[d112crzy]

There isn't an actual set AFR for one thing, just a general afr to tune for on the street.

To really find what is best you'll need to get on the dyno.

But as a general, 14.7-15.5 during idle/cruise. 12.7-13.3 for NA setups and 11.7-12.3 for turbo setups. This is on unleaded fuel. It will change if you went to e85/straight methanol or any other fuel type. But that's why there's lambda. Stoich always =1 in lambda.

[bcjammerx]

I'm thinking for street tuning prior to dyno...if I had such capabilities to datalog etc etc.

Trying to figure out where i would need to be (n/a or boost...course for me n/a for now)

Another attempt to learn a bit more before I have the parts to blow up...so I will be less likely to blow them up when I do get them.

...gooood...gooooooood

[turbo90accord]

Most manufacturers will tune the EFI system to run between 11.5:1 and 12.7:1 in the high load , mid-upper RPM range for optimum power and engine reliability, while running mixtures near 13:1 at slightly lighter loads. For even lighter loads, the EFI system switches into a “closed loop” feedback system that targets 14.7:1 for optimum fuel economy and emissions using the o2 sensor to monitor stoichiometric 14.7:1.

I personally dont use the a/f ratio or the 14.7:1 scale to tune. I use what is called lambda which i personally think is easier to tune with where instead of 14.7 being stoich the readout will be 1 and i tune to .85.

Octane like said above is going to be more of a timing thing rather than airfuel ratio and timing is more propperly monitored via EGT and torque curve on a dyno rather than a/f ratio.

max lean also differs from engine to engine and is really hard to tune. There are piston designs and many other factors that can allow people to run rediculous airfuel ratios but does depend on load.

Just remember when you first start tuning its mandatory to use a wideband and a really good idea to start off rich in your mixture.

[chessboxer]

I'm thinking for street tuning prior to dyno...if I had such capabilities to datalog etc etc.

Trying to figure out where i would need to be (n/a or boost...course for me n/a for now)

Another attempt to learn a bit more before I have the parts to blow up...so I will be less likely to blow them up when I do get them.

...gooood...gooooooood

Dyno tune first, to get your ignition timing right, and then do a clean up tune on the street to clean up afrs.

Also, as has been stated, each type of fuel has a different stoich rating. The amount of fuel required will vary per type of fuel, and also, higher octane only means that the gas is more resistant to detonation, meaning you can run more aggressive engine timing, which generally makes you more power.

[bcjammerx]

thanks for the info, I'll have to read up more on lambda as well