13 AFR: Preying on the Blissfully Ignorant By Virtue of “Education”

I will just come right out and say it: when doing performance engine tuning under no situation is it “OK” to run a forced induction engine lean, regardless of the fuel you are using.

I thought I had seen all the hack job work I could imagine in this industry, but the strive for more and more power on Direct Injected vehicles has hit a new low. As the injection window runs out performance “tuners” and companies claiming to be “industry leaders” are resorting to leaning engines out to unacceptable ranges to post “performance figures”.

I’ll say this as well: it’s your car, do whatever you want to it.

However when you take your car to a “professional”, it’s frightening to imagine what they might actually be doing. It’s one thing for a garage level tuner to make questionable decisions, but it’s another for someone claiming to be an “industry leading” tuning solution supplier to do the same thing — and then defend their poor decision making with even sillier excuses and passing it under the guise of “education”.

“Teaching” poor decision making and questionable tuning practices is not industry leading behavior — it’s hack job work. They must think we were all born yesterday. One also begins to question if they even understand what they are actually doing, at all.

Those D/I Limits

With direct injection — you have a much shorter injection window. Once you’re out of fuel, you’re out of fuel. As it stands right now it’s impossible to just “upgrade” the injectors or the D/I fuel pump on most platforms to give the motor the fuel it needs.

As a result we’ve seen various D/I platforms (WRX, Corvette, now Honda) run the motors leaner and leaner. We’ve also seen plenty of motors with failures that could of been avoided — melted pistons, damaged ring lands, scorched cylinder walls. Just because it hasn’t happened yet, doesn’t mean it won’t.

Those AFRs

For the sake of discussion — we will not use AFR units, we will use lambda. In Gasoline units 1.0 lambda is 14.64 AFR, 13.0 afr is 0.89 lambda and 11.5 afr is 0.78 lambda.

When discussing “AFR” and the function of fuel for the sake of the motor — you need to understand it. Under normal situations, a stoichiometric air/fuel mixture (1.0 lambda) is perfectly fine — cruising, idle, low loads. However as load goes up (and boost goes up, etc), the motor begins to create more and more heat — so you add more fuel by “enriching” the mixture (targeting a richer lambda, say 0.78), this provides the extra “charge cooling” the motor needs to prevent detonation and in many cases allows for more ignition timing to allow the engine to make better power.

However, if you chose not to enrich, or not enrich as much, say — 0.88-0.89 lambda (12.8-13.0 AFR in gasoline units) under boost, what happens? The motor gets a little bit of cooling — but under F/I conditions far from optimal. Does it refuse to make power? No. Let’s get this clear: you can absolutely throw a ton of boost at a motorĀ  and never even enrich at all and it will make some power, for a while. How long? Who knows, YMMV.

It will not, however, make optimal power and will run hotter, which will require a reduced timing map. If you do not reduce timing, you can suffer fits of detonation — and yes, some fuels are much better resisting it than others. The amount of cooling a fuel supplies is relative to volume — which is why it’s common to see 0.75-0.78 lambda under boost vs something like 0.85 lambda on a naturally aspirated motor.

The Excuses

The most common excuse for this kind of behavior — is that X or Y OEM does it. Let’s be clear, a lot of OEM’s will run engines quite lean in boost on factory forced induction platforms — for a TIME (IE: BMW, Ford and now Honda). They are generally tuned to enrich, and in many cases, enrich very rich after a short timer has expired under load.

The OEM’s also do not tune with performance in mind — they will reduce ignition timing very aggressively and run boost levels much lower than the turbo is capable of in most cases. They are delivering a reliable vehicle as a PACKAGE while keeping EMISSIONS under control . So there is a lot of give and take. They make that 1.0 lambda under boost for a short time “reliable” by reducing timing very aggressively to keep in-cylinder combustion temperatures down.

I’ve never seen an engine being tuned for performance by the aftermarket with emissions control as their goal — it’s always the search for more and more power.

So to be clear: if you throw 29psi at a motor and run it at 0.89 lambda, it will make some power. I’ve never seen a turbo motor live happy at 0.89 lambda and make best/clean power there — enrich it to 0.78 lambda and watch it come alive.

A great example here is the FK8 Honda Civic Type R. From the factory it comes running 1.0 lambda to about 4000 rpm if you start a dyno pull from down low. We will actually MAKE MORE POWER with lower boost than the stock tune. How is this possible? We enrich it to 0.8 lambda (11.7 gasoline AFR), and with the extra enrichment the motor automatically picks up power — before we even touch the timing map. Mind blowing, right?