Power vs AFR

I suppose most people aim for 14.7 (dependent on fuel) for most rpm driving and 12.5-13 afr for wot?

My question is why 14.7 or even leaner for cruise, other than emissions or gas mileage?

Would you gain more power through the rpm band by running a richer mixture say in the 13s or along those lines? Obviously sacrificing gas mileage but depending on application who cares for mpg? Lol

When i read Master EFI tuner he aims for 12.5 through the entirety rpm range for best safe power (medium large cammed ls1).

Just overthinking stuff here looking for opinions.

why burn more fuel than you need , youre not looking for big power at 1500rpm less than 1/4 throttle.

I would go with no, it wouldn't make any more power. Ideally if you run stoich 14.7 for gasoline you there would be just the right amount of air and fuel to use up all of the fuel. When you go richer than stoich it is pretty much for the cooling aspect that extra fuel gives to help detonation. Maybe if you ran slightly richer you could add more timing and make more power, but it seems like you could just give it a little more throttle and achieve the same thing with less fuel consumption. Plugs would probably get fouled sooner also. I have also noticed though in tuning that I messed around with different PE settings and if it adds too much fuel at lower throttle positions or lower rpms like maybe like low 12s afr it seems to loose power. I think its kind of a balance that you would have to use a dyno to find out stuff.

when tuning for best cruise torque i use the cruise control and a road i can use same part every time then i make any timing or fueling adjustments and set cruise at same speed and see if the instant fuel usage is better or worse as that takes into account all variables like throttle, spark, fuel, load so if they all work together to make best torque u will get lower fuel usage, if u just lean it out or richen it up or more/less timing the instant fuel usage will show u if its working better or worse if u stick to same speed same road, even with a camshaft overlap the eoit can make a decent change to instant fuel usage especially if its in the wrong direction

combustion has a beginning and end

Look at the graph of pressure inside the cylinder
Attachment 101167

Now imagine if you put the exact amount of air and fuel necessary to complete the reaction... 14.7:1

When the reaction starts you are pre-TDC and some of the fuel is being burnt before it has a chance to produce torque
In fact as the reaction builds and reaches TDC there is 0 net torque(forcexlength = 0 at TDC) even though a very high pressure may be produced in the chamber, which is using up fuel molecules and oxygen.

Reaction at the beginning and end is all wasted fuel. So if your mixture contains the exact amount of fuel necessary from one end to the other, you will lose a lot of torque because there was no extra fuel component to react during the critical rod angles where torque is produced through as maximum mixture reaction is desired.

As the piston descends the volume of the chamber is going up so the design of the chamber and piston surface is often controlled to facilitate the reacting of fuel and air through the critical rod angles more-so than the beginning. This is why there is such a large timing window for modern engines (where it seems like no additional power is gained with +/- large increments as long as it falls within some range).

What we really want is to nurse the piston through TDC, then wait until the rod approaches useful angles for torque, and THEN react as many air and fuel molecules as possible through that window.

So what we do is run rich. It spreads out more fuel molecules to combine with oxygen, so the oxygen doesn't have to 'search' for fuel, there is no 'waiting' for it to find partners because there are so many extra fuel molecules hanging around. Remember chemical reactions depend on COLLISIONS with other molecules and a large part of why gasoline is 93 octane and not ZERO octane is due to steric hindrance or the physical shape of the fuel molecules 'getting in the way' of finding partners (so the reaction slows down).
You put in extra fuel molecules when you want more power, to ensure that there are plenty of un-reacted fuel molecules available during the critical rod angles where torque is made.

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Originally Posted by anniversaryss

I suppose most people aim for 14.7 (dependent on fuel) for most rpm driving and 12.5-13 afr for wot?

My question is why 14.7 or even leaner for cruise, other than emissions or gas mileage?

Would you gain more power through the rpm band by running a richer mixture say in the 13s or along those lines? Obviously sacrificing gas mileage but depending on application who cares for mpg? Lol

When i read Master EFI tuner he aims for 12.5 through the entirety rpm range for best safe power (medium large cammed ls1).

Just overthinking stuff here looking for opinions.

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It helps to consider that the throttle exists to reduce power output.

If the power requirement stays constant (e.g., cruising on the highway at a steady speed with a steady grade and in steady wind) and our hypothetical richer mixture made the engine more powerful for a given set of conditions, the net effect is we would use less throttle angle, but significantly more fuel, to provide that same amount of power - fuel consumption, emissions, etc. increase with no benefit to the driver or vehicle. We typically want the most throttle angle reasonably possible for cruise and light acceleration to bring up fuel economy and reduce emissions.

That's the beauty of PE - when we approach conditions where that extra power is desired and beneficial (WOT), we can take advantage of that enrichment, but without the drawbacks of driving around similarly enriched the remainder of the time.

I like that explination.

I actually smacked myself for this question and figured it was dumb. Do what we always do.

Tune for stoich and just bring PE in earlier at desired throttle/rpm to get that power when you want it instead of running the mixture a little rich at all times.

I think its good to think outside the box. I like trying different stuff and see if I like it or not

PE is strictly a OEM ecu thing. No other stand-alone I've ever used (haltech, AEM, megasqrt, big stuff, PFC, etc...) uses PE.

instead you just tune the VE map however you want it to run. The enrichment comes from the VE map itself (or whatever kind of map the stand alone is using which is similar to a VE map... its not always "VE")

I tune my engine like this for best economy and power:
0-10KPA 13.8 to 14.2 "lift" region- keep it slight rich to prevent tip in fuel error issue and help cool the chamber between transitions if using a manual transmission
10-20KPA 14.7 to 14.9 "about to lift"- keep it economical for coasting with slight pedal input but not too lean for tip in issues
20-30KPA 14.9 to 15.5 cruise region with light load can be as lean as 15.8 or 16.2 is fine.
30-40KPA 14.9 to 15.2 cruise region with some load
40-50KPA 14.9 to 15.2 cruise with load in heavy vehicles (or numerically low gearing) and idle region
50-60KPA 14.7 to 14.9 coming out of cruise, accelerating up a hill, etc..
60-70KPA 14.4 to 14.7 give it some fuel for acceleration but keep is economical if desired
70-80KPA 13.8 to 14.4 more fuel to wet things down, get ready to accelerate fast, keep it cool, give it some torque
80-90KPA 12.5 to 13.5 power a/f ratio approaching WOT
90-100KPA 12.0 to 12.5 full WOT gets all the fuel you care to spare
Now boost
100-120KPA 11.5 to 12.0 keep it near 12's for spooling the turbine
120-150KPA 11.3 to 11.8 typical a/f ratios at 7psi of boost for most engines, works well
150-200KPA 10.8 to 11.2 typical a/f for stock engines (fragile cast pistons) very safe and the LS specifically LOVES the 10.8 to 11.0 region in boost from what I can tell (experience)
200+ typical 10.8 is my target from here out on gasoline. Depends on the fuel quality at this point.

Carburetors figured out how to do that - lean at cruise, rich for power - more'n a hundred years ago, with nothing but dumb springs and diaphragms. :p

that would completely depend on what jetting and how the carb is set up

That's a weird and irrelevant argument to make. What's the current state of repair of any one specific individual carburetor have to do with carb theory of operation?