DavidDeco

[Sorry mods...I double posted this because no one barely posts on the Power FC forum and it wasn't specific to that anyways...]

Okay, I'm NOT a tuner (this will be obvious in 2 ms)

WHY, please pray tell with excruciating detail, does everyone tune for 11.1 to 12.1???

Obviously there is a safety factor involved but I'd love to hear the wisdom behind it rather than just hear it spatted out as some law. (perhaps good law, but I just want to know how it was arrived at).

Basically, isn't 14.7 ideal air/fuel mixture? So why 12.1or 11.1? PLEASE don't be generic and just say for safety. or because of turbo boost, I know that there is some saftey zone I just want to know how these became the magical numbers.

1bad7

u wanna be between 11.0 and 11.5 throughout the rpm band. anything richer and ur losing power, anything leaner and ur risking detonation.

DavidDeco

I understand the theory but why 11.0 to 11.5 if a consistent 14.7 is ideal and thus I'm well below lean IF I can show a consistent 14.1?

Someone chirp in and tell me some extenuating factors that may push me past ideal and describe how.

Otherwise aren't I better off running at least 13's or low 14's?

I know there has to be a reason everyone states this, but I just can't find the answer

Cheuk in Seoul

I believe 14.7:1 is ideal for both power and fuel economy/ effeciency. Around 13:1 give the best power... but it is a curve. Below 11:1, you begin to fall off the power curve. Leaner will give you more power but like everyone says.. you give yourself less room for error / detonation.... not due to the air/fuel ratio, but detonation due to poor octane fuel, boost spike, carbon build up... etc.

ptrhahn

iTrader: (9)

I'm pretty sure 14.7 is for piston engines running no boost.

DavidDeco

Thanks, we're getting there

But why 13:1 - 11.1

Where did this 2 difference come from.???

Is it just an aribitray empirical number to make people feel safe or is there some more rationale behind it??

Again, I understand the safety matter. I just want to know why 11.1-12.1 is the chosen number. If an engine runs on 93 octane it's entire life (in 9 years I've never deviated from a "stated" 93 octane) can't I pick a more agressive number?

Or how about posing the question this way:

IF I RUN 93 OCTANE ALWAYS/100% no exceptions, have a boost controller that never deviates more than 1 psi, and my car has new spark plugs and wires every 15k, what is the safest A/F I can run for maximum power with a moderately safe margin????

EDIT : Even more so, a mechanic I know (non Rotary specialist) asked me why as well. He says he tunes for ideal. I don't think Rotary or Turbo's change the ideal factor (maybe I'm wrong) but more likely just the error margin....

Flybye

Remember that the factory fuel maps are designed around X fuel ratio with the stock components. Once you begin to install aftermarket goodies, you throw that a/f ratio all over the place. Which is where the tuning comes into play.

Now.... it Is true. To a certain degree, the leaner we run, the more power we get. Basically, the leaner you run, the better combustion you will have, BUT if you over boost, if you suddenly starve the engine from a small amount of fuel that was suppsed to be there, you detonate and run the risk of blowing an apex seal. There are guys that have NO trouble running at the limit(13.1), and there are guys that prefer to run a SAFER margin(11.1), and to run a safer margin, they run richer.

Moral of the story, DEPENDING on your mods and the tuning of your ECU will depend on how much of a safety margin you want to run with your a/f ratio. The guys that run their systems at the edge are usually the guys that only use their car for the track when they know the environment is set directly for how the tuning has been done.

DavidDeco

Thank you. I have the 1:1 RRFPR and a Cosmo Pump w/ 1300 sec. I think I've updated my Fuel System enough for stock turbos. My plan was to run 13 psi normal and 15 psi "on those special occasions" once broken in.

I will have a WIDEBAND (FJO) installed within the next few days so assuming my A/F readings are very accurate, What is a relatively moderate A/F setting to shoot for then ??? I really don't thik in my limited knowledge that I'm in danger of going lean with this setup. Can't I afford to dyno tune it with my FJO in the 13's safely? Or is this a bad idea?


One additional note - I have a Power FC with the Michel map except for the lower right quadrant which I left alone. My other changes have been Fan Temp and the 1300cc secondaries with .04 to .16 lags.

Wade

iTrader: (1)

Tune your car for 13:1 and you will probably blow your engine quickly. Running 11:1 instead means more fuel in the chamber which helps cool the intake charge and make detonation less likely. These numbers weren't dreamed up, they were found from experience. I really don't think you'll gain any power going leaner than about 12.5:1. There is a point when you will lose power from being too lean.

The stock ECU runs at 10:1 or RICHER, keep that in mind. Any time you tune leaner than that, you necessarily increase your risks of engine failure. Not to mention, most aftermarket computers have no knock control like the stock ECU. You can tune for 11.5:1 and gain power compared to the stock ECU, and with the right setup, this is really safe. But it is still likely not as safe as the stock ECU.

This is one reason it peeves me when people call the Power FC or other computers a "Safety Mod", the PFC base maps appear to be leaner than the stock ECU AND it loses the stock knock control feature. Explain to me how that would improve reliability. Granted, there might be only a minor loss of reliability when the PFC is tuned properly, but it appears 9/10 people don't get them properly tuned. <rant off >

Wade

pomanferrari

iTrader: (1)

Hey Wade, is the knock control disabled in the PFC? So I should be running a J&S knock sensor? But didn't people have problem with the J&S retarding with the PFC doing its thing so that you end up with the trailing firing before the leading?

RX7Elmo

i don't even think NA Hondas run as lean as 13:1 or tune for it. Of course it is ideal to burn 14.7 meaning that for every molecule of fuel and air, they both combust.

One reason why most FD owners will tune for around 11.5:1 or so is because it's experiemental. we've seen people that are leaner go out with bad motors, while those that tune for 11.5:1 have good running powerful motors that last.

Say you tune for 13.0:1 and have a great boost controller and etc etc, you still can't account for ambient temps, humidity, and constantly good fuel. One little thing goes wrong and an apex seal could be gone.

danny

SPOautos

Well the PFC does run a little leaner, its not lean however. The stock tuning is just to rich. The PFC is a saftey mod if your running over 10psi of boost.

Rotaries have problems with heat. The leaner you run the more heat you generate and the more heat that the inside parts of the engine are absorbing.

Actually most of the forced industion piston engines I've seen that have been dyno tuned and are running alot of boost also run a/f mixtures in the 11's.

When you are tuning your fuel at light load (like vacume when cruising, ect) you can run closer to 14 a/f just like a piston engine thats n/a.

You start raising the compression sky high weather it be with extreme high compression pistons or boost and you either need to run the car rich or run race fuel or run water injection, you turn it way up like 20+psi of boost and you'll be running a combination of those things. The reason you do this is for the cooling properties, running extreme high compression creates alot of heat.

I'm sure there are other reasons but here is some info for you to chew on for awhile. If your mechanic doesnt know this you might have cause to worry if he is tuning you rotary. Just make sure he(or you) tune to low/mid 11's with L timing around 13-15 at full boost and you should be ok.

STEPHEN

mjw

iTrader: (1)

I'm going to chime in quickly here..

14.7:1 is ideal for cruising only, partial throttle conditions like a long drive on the freeway

11:1-11.5:1 is what you want to shoot for on a rotary. Because of their size/power output ratio they generate a lot of heat and need the extra fuel to cool the intake charge, prevent detonation etc..

12:1-12.5:1 is a good target for boosted piston motors. I used to have a 90 supra turbo running all HKS electronics and a 60-1, I tuned the car for this and it made gobs of power. The motor could handle the leaner condition because it generated less heat, and can weather slight detonation.. not that it is a good thing.

When we talk about tuning for WOT throttle conditions the ecu is operating in an open loop mode and ignores the O2 sensor output. The O2 sensor is used for cruise conditions the obtain optimum gas mileage (closed loop).. this is why it is a terrible tuning device for WOT, it is only accurate/sensitive to leaner, partial throttle conditions. HTH.

Matt

j9fd3s

iTrader: (3)

14.7:1 is where the least amount of pollution occurs, it has nothing to do with power orthe way the car runs.
before any cared about pollution controls, most cars are set to run richer than 14, more like 13ish, because that where they run the best.
rotaries like to run richer than this, http://personal.riverusers.com/~yawpower/carbtun.html
even though hes not talking about a turbo car it still somewhat applies.


mike

pomanferrari

iTrader: (1)

In fact, the Audi R8 twin turbo V8 runs a higher than stochiometric mixture due to the direct injectors squirting fuel at 3000 psi. The direct injectors inject directly into the combustion chambers and are aimed either at the cylinder wall or the piston to get swirl. I think that it's a stratified combustion mode that they're running, i.e. WFO all the time like a diesel. The swirl is a fuel volume that is actually quite rich and therefore the fuel doesn't detonate.

They get very good gas mileage compared to non-direct injection cars; something like 10% better than their previous V8. Don't quote me on the figures though.

j9fd3s

iTrader: (3)

the air fuel ratio the engine is happy with has a lot to do wih manifold, port, and combustion chamber design. it really depends on how the air fuel charge is distributed in the combustion chamber.

mike

Dragon

14.7 is ideal for a piston engine.. the combustion process in a rotary is way way way diffrent... if you try to run anything near this air/fuel ratio you engine will go pop and sputter at even low boost levels.. and blow at higher boost...