I recently made a quick and dirty warm air intake (WAI) out of the stock MAF housing a flow stack and some couplers. This post will cover the tune changes in layman's terms and the dangers of intakes without a retune.
Keep in mind this is just a proof of concept intake and is not meant to be permanent in it's current state. It's function is similar to a lot of non-airboxed intakes on the market.
Did a log with the new intake and compared it another log from the same road. As you can see I stopped doing the pull around 4500rpm, I didn't want to risk it going further.
First thing that really stands out is much leaner AFR's, about 3 points leaner, instead of a good and safe 10.5-11 AFR's, car leaned out to 13-13.5 AFR. Next thing was overboosting, about .5psi more. Running more boost and being lean will absolutely destroy your engine. As you can see my AFR's were in 13's, when max safe is around 11.5 AFR on stock TMIC.
Now that we covered the easy to spot things, lets look at the hidden reason behind such drastic AFR changes.
Mass Airflow (g/s)
Not exactly sure why, but the less restrictive intake caused the mass airflow reading to be much lower, about 25% lower. The ECU basically thinks that we are receiving less air, thus it adds less fuel through the fuel maps when in fact we are receiving more air then before.
My thought on this is, it should have been reverse, more airflow from intake should cool the MAF hot wire more, needing more voltage to keep it warm, thus reading higher MAF Voltage, which calculates to a higher grams per second airflow. Maybe someone more knowledgeable on this can chime in?
Engine Load (g/rev)
Because the ECU is calculating lower grams per second, our Engine Load grams per rev is now much lower.
This can be visualized through the trace line. We are stuck at 1.80 g/rev instead of 2.40 g/rev. On this map 1.80 g/rev is meant for about 7psi of boost and 2.40 g/rev is meant for about 14psi. New intake overboosts to 14.2psi and stays at 1.80g/rev, this causes the car to run 7psi's fuel values while your actually at 14psi.
Not only are you running leaner, you are also running more timing, this as because we are stuck in a lower column meant for less boost.
Further visualized in this map trace (ignore the bottom trace for now). As you can see the car is running 21* instead of 13-17*. That alone, even with non lean AFR's can kill a motor.
Tuning for these changes
Finally, if you haven't been pushed away from intakes all together, we can start adjusting the tune for this mod. These are just the basics, keep in mind that every intake is different and might not be as easy to adjust the tune for (especially if the MAF tube diameter and MAF placement is different from stock).
MAF Sensor Scaling
First I calculated the difference between the Mass Airflows between the two graphs and came up with about 24%. I increased the MAF Scaling by 25%.
Initial & Max Wastegate Duty Cycle Tables
Next I calculated the difference between the amount of boost I was running, came up with 7.7%, removed 8% from all of the values.
Here is the boost map trace, we are back to our previous boost numbers. Now you could always keep the added boost and just adjust your timing and fuel for added PSI, but I personally wanted a 1:1 comparison of the power gains from the intake only.
Primary Open Loop Fueling
I didn't have to make any changes to the fuel table because my AFR's were identical to what they were before.
This map trace compares the three runs AFR's, as you can see the most MAF scaling increase and boost decrease AFR's were back to what they were before.
Ignition Base Timing
At first I didn't have to adjust the timing, but driving higher IAT (which a WAI intake is more prone to higher IAT's) I saw some knock and reduced timing up top.
Timing Compensation (IAT)
Warm air intakes soak up a lot of heat and hit high IAT's (Intake Air Temperatures) much faster then with stock intake. On a 90*F day sitting at a stop light and slow city driving got me 150*F in just a few minutes. I saw the ECU pulling timing due to knock at fairly low loads (1.00-1.20g/rev).
You should probably update the Timing compensation table to retard more timing at higher IAT's to avoid detonation.
The stock intake is a very good cold air intake, but while it can deliver colder air it's still very restrictive. The common notion that an intake is not needed or doesn't gain any power below 300-350hp has been debunked by GrimmSpeed, with their intake making around 20whp over stock intake at similar boost levels and minimal tuning. Their intake did so well because it has minimal bends and has a very well designed airbox that reduces hot engine air contamination.
When my IAT's stayed down (drive around for couple miles before doing the pull) I saw similar gains in Virtual Dyno on the same stretch of road 30 minutes apart.
The biggest issue is with a new intake is MAF voltage being less, which gets calculated to lower engine load, which makes your ECU to run less fuel and more timing for the same amount of boost.
Next issue is WAI specific: keeping the IAT's low to avoid timing retard (less timing = less power) and to avoid detonation. Thus I now believe a sealed Airbox is a must, either buy one with it, or make one for your existing intake.
I also found that keeping the MAF location and diameter the same as stock (because I'm using the stock maf housing), still requires a retune (now this could be because of the flow stack, if I get a regular cone filter I'll test this out more).