By: Haitham Alhumsi
The tuning calculator helps you tune your car by calculating:
- The ideal Air to fuel ratio
- Total timing value
for your engine based on the data you input into the calculator.
Now the concept of tuning your engine can involve alot of things including your static compression ratio, your available octane level, the choice of fuel (alcoholic, oxygenated, nitro-enriched…etc), as well as certain parameters that in this day and age are customizable through your ECU, namely:
- Fuel injection
- Timing advance
- Cam timing
Any proper tuning effort needs to address all three parameters to maximize mean best torque (MBT) in every rpm point and especially in your target RPM range (which might be 3000 rpms for a street car or 9000 rpms for a drag car).
The horsepower calculator and the built in tuning calculator will help you make a series of correct decisions when it comes to fuel, timing, compression, and camshaft selection.
There are also some aspects to tuning that are more qualitative than calculated. To explain timing advance and camshaft timing in a qualitative sense, please continue reading the four articles below:
1- Tuning your timing and timing trends
2- Supercharger tuning through cam selection and cam timing
3- Taming the Untuneable – OBD2 Engine tuning guide
4- Taming the Untuneable – Part 2- OBD2 Engine tuning guide
Tuning your timing and timing trends
Hi , it’s Haitham again and this is another one of our.. how-to videos around the Power calculator on Supercharger Performance .com
What I’m going to talk about today…
is timing advance and tuning your ignition curve.
First we’re going to talk about some of the underlying concepts of ignition timing and timing advance
Then we’re going to look at some simulated timing curves
Then we’re going to summarize with some insights on how you can use this information to increase your horsepower by advancing or retarding timing, in the right places to gain more power.
First of all, let’s look at a 4 stroke engine animation …
This is top dead center… when the piston is all the way up the bore
This is bottom dead center … when the piston is all way down the bore.
Usually when when we talk about timing advance, we talk about ‘B.. T.. D.. C.. ‘ or before top dead center.
Usually the spark plug ignites the mixture before the piston reaches top dead center in the compression stroke.
Now the reason why we fire the plug ‘early’…
is that the mixture of air and fuel (and possibly water, methanol, or nitrous) takes some time burn…
and so the flame front takes some time to travel outwards and consume all of the air inside this top volume (comprised of the cylinder head volume, and the piston surface volume if the piston is dished)…
once the flame has consumed a large portion of the air fuel mixture… this flame, trapped between the piston and the cylinder head, creates ‘peak cylinder pressure’ and it is this cylinder pressure and expanding flame that pushes down on the piston making it rotate.
Now the trick here is that you have to synchronize the piston rotation, with the flame front burn rate so that you can hit the piston with peak cylinder pressure just after it cross top dead center and thus deliver ALL the force of the combustion into the rotation of the engine.
If you advance timing too much, you catch the piston on it’s way up and slow down it’s movement losing power
If you retard the timing too much, the piston outruns the flame front and very little power is transfered from the combustion into rotation
So there is a ‘perfect’ timing setting based on these two things:
piston speed: which is affected by RPM, and by Rod/Stroke ratio
flame front travel speed: which is affected by factors like mixture density, fuel to alcohol ratio, compression ratio…etc
Now let’s talk a little bit about the two main factors affecting timing advance:
The first is RPM. As RPM increases, the piston speed increases.
The thing is that the piston speed increases linearly with RPM … but the flame front travel speed only increases slightly with RPM due to more turbulance in the cylinder and a better mixture of air and fuel which allows the ‘fractal’ moving flame front to travel faster.
So going from 700 rpms to 7000 rpms, the piston increases it’s speed by a factor of 10, but the flame front only increases it’s speed by about a factor of 3.
So in a sense the piston is OUTrunning the flame front, and to re-synchronize the mixture so that we can catch the piston at top dead center we need to further advance the ignition timing.
To make up for this effect, the timing advance at 7000 rpms needs to be about 3 times the timing advance at idle and that’s how ‘mechanical timing’ came to be starting with a base timing of something like 10 degrees BTDC and growing out to 32 BTDC near redline if we’re talking for example about a large bore engine).
The second factor is mixture density. Which is typically measured by the car’s ECU with RPM, Flow and temperature sensors… But for this example we’re going to measure it in terms of Volumetric Efficiency since we can calculate that figure.
As the mixture increases in density, then so does the number of air and fuel molecules available for the flame front to expand outwards. This denser mixture allows the flame front to travel faster, as is typically the case with forced induction engines such as turbocharged and supercharged vehicles that cram more air and fuel into the cylinder.
If we leave this mixture alone at stock timing, then the air fuel mixture will out-accelerate the piston and catch it BEFORE top dead center which slows the engine rotation and exerts power rather than making it.
So as mixture density increases we retard timing to catch the piston once again just as it crosses top dead center. As the mixture density decreases, we advance timing to prevent the piston from outrunning the now slower moving… & less-dense mixture.
Of course there are other things that affect flame front travel speed besides mixture density…
octane rating (higher octane fuels burn slower)
the presence of burn accelerators such as nitrous oxide and oxygenated alcoholic fuels like ethanol and methanol,
or the presence of flame retardants such as water injection and high humidity.
Now that we have a basic understanding of timing curves, let me show you some simulated timing curves based on the 5.7 liter LS1 engine.
Now let’s talk about the advantages of knowing this information…
Different VE curves for modified cars
Not leaving any power on the table (nitrous or superchargers)
The Apexi S-ITC is an older generation piggy back controller. The S-ITC stands for Super Ignition Timing Controller, and had a +/-15 degree advance/retard setting adjustable at 5 RPM points between idle and 7000 rpms.
At the time when this box was released, most timing controllers were either basic boost based retards such as the MSD BTM (boost timing master) or a fixed single externally triggered retard box for nitrous activation…etc
So, at the time, this product was much more advanced than the cruder forms of ignition tuning available by competitors. However, this product sold very poorly and was quickly discontinued.
The primary reason for the product’s failure was not the product itself, but rather lack of information in the general community about proper ignition tuning and the power potential that was being left on the table with un-tuned cars.
I hope that this how-to video here gives you a better idea about ignition tuning (since very few people actually discuss this aspect of supercharger performance and engine tuning in general). Even though the tools have changed over the years (and now we have full 16 X 16 timing maps that are 100% tunable to your desired timing), the basic theory remains the same, and the thirst in this community for this information is still there.
Supercharger tuning through cam selection and cam timing
Camshaft tuning is an essencial part of supercharger tuning. Camshafts orchestrate the valve opening and closing events in the engine and decide whether what comes out of our motor is beautiful high power music, or a mess of dysphonics.
The use of the proper supercharger optimized cam shaft can go a long way towards supercharger tuning and give considerable power gains for the money invested.
To understand camshaft timing and camshaft selection we have to understand first:
Changing when the valves open or close (intake or exhaust) changes the the valve timing with respect to:
- The piston position inside the cylinder. Depending on where the pistons is in the stroke, and where we are in the combustion cycle, then opening the valves will exploit the pressure difference between the cylinder and the intake and exhaust manifolds.For example it would make sense that the ideal time to open the intake valve is when there is peak vacuum inside the cylinder so that when the valve opens, the maximum amount of fresh air can be ingested. Similarly, it makes sense not to open the exhaust valve until peak cylinder pressures have been achieved inside the combustion chamber and the combustion is complete and all the power is extracted.
- The high and low pressure pulses created by the design and runner lengths of the intake and exhaust manifolds.It would make sense to open the intake valve just as the reflected pressure waves in the intake manifold reach the intake valve as a high pressure portion of the wave, thus opening the valve at this high pressure point gives a ‘ram air’ effect through volumetric effeciency resonance tuning increasing air ingestion which increases power.Similarly on the exhaust side, it makes sense to open the exhaust valve, just as the reflected low pressure (vacuum) portion of the exhaust wave (reflected back from the collector) reaches the back of the exhuast valve. At this point in time there is both peak pressure inside the cylinder, and vacuum in the exhaust which creates a higher pressure differencial and a faster evacuating exhaust gas.
- With respect to the ignition timing event, for example a shorter duration or advanced exhaust cam, opens the exhaust valve sooner with respect to when the mixture was originally ignited, this means that although by advancing the exhaust cam we may have matched our header design and opened the valve with the lowest possible exhaust back pressure for best effeciency, at the same time, we have reduced the amount of time that the mixture is combusted and possibly opened the valve before reaching our peak cylinder pressures and thrown away some horsepower.
- The intake valves with respect to the exhaust valves: and this is usually described in terms of lobe seperation angles (the offset in degrees between the center of the exhaust cam and between the center of the intake cam), or in terms of how many degrees of overlap (the number of degrees that both intake and exhaust valves are open at the same time).
Since the combustion inside the cylinder occurs at a much higher pressure than atmospheric pressure, and since exhaust valves are usually smaller than intake valves (for this same high pressure reason) then exhaust gas velocity is much higher than intake gas velocity. So, in some engines it is beneficial to open the intake valve earlier than usual during the last part of the exhaust stroke, this is called overlap. During overlap – at the very end of the exhaust stroke – the amount of pressure left in the cylinder is low so it is possible to breathe in new air under atmospheric pressure, at the same time, the high velocity of the exhaust gasses exiting help draw in even more fresh air from the intake side in an effect much like ‘syphoning’ where the fluid (in our case air) flows as a continuous stream drawing in new intake air after the old exhaust gas leaves.
The other part of phenomenon that relates to timing intake vavles with respect to exhaust valves is the duration of time where both valves are absolutely closed, which is your power stroke. This is the part of the combustion cycle where the mixture can be compressed and combusted. If either (or both) intake or exhaust valves are open you will not be able to neither compress nor combust the mixture, and the absolute duration of time (in degrees of rotation) that your mixture is combusted and allowed to reach peak cylinder pressures is affected by camshaft selection and cam timing. One thing to note is that the valve angle has alot to do with exhaust scavanging, obviously you will get maximum scavanging if the exhaust and intake valves had ‘line of sight’ i.e. if the valves were seperated by an angle of 180*. If so, the exhaust air can directly pull in new air. Conversely, you would have the least possible scavanging if you had valves that were at a narrow angle (zero degrees at the extreme) between each other, so that the air would essencially have to make a U turn to come in through the intake and get pulled out the exhaust.
So different motors respond differently to overlap depending on the exhaust back pressure and the valve angle.
Cam duration is the number of degrees of the entire 360* rotation that the intake or exhaust valve is open. The longer the duration, the more air you can get into the motor, the more overlap you have (which helps more with higher rpm power performance), the shorter your power stroke is (which reduces your combustion duration and your peak cylinder pressures reducing low rpm fuel effeciencly and clean idle….etc
Increased duration (with it’s increased overlap and scavanging) also gives the opportunity for exhaust gasses to get to the intake, or intake gasses to leak to the exhaust, and so are more sensitive to proper timing events otherwise we can get some negative effects from being ‘overcammed’
Lift is how far or how deep the valve opens into the cylinder. The more lift you have, the less the valve is a restriction to incoming air because it is farther away from the direct path of entering or exiting air. Adding lift in general adds power to all rpms, depending on how well the camshaft (and valve train) can accelerate the valve to a higher lift number in a short duration. It’s like a ramp, the shorter the duration and higher the lift, the steeper the ramp. So what happens here is that if your valve train isn’t light enough and well controlled (Through proper valve springs or hydraulic lifting and damping) to operate that rapidly then lift will give you improved performance at lower rpms (where there is alot of time to move the valve to peak lift) but reduced performance at higher rpms, where there are more rounds per minute and so less time per round, and thus less time to go up the steep ramp and push the valve out to full extension.
Lift is good, but usually people don’t try to radically increase lift on their aftermarket cams because of a few considerations:
- Make sure that at this new lift, that there is still enough clearance between the valve (at full extension) and the cylinder (at top dead center) to prevent any catastrophic mechanical failure.
- Upgrade to lighter valve train, with stiffer springs or dual valve springs to have more control over the valve with this steeper cam profile.
- It does add power but it doesn’t shift the power curve up or down as radically as chaning cam duration does, and so in most aftermarket applications we really want a cam to give us peak power at a certain rpm range and so we care much more about the best duration (and some added lift).
I know this is a somewhat complex topic, but I need to make sure we’re speaking the same language before we go into how this relates to superchargers. Before you decide which camshaft to use (or how to adjust the timing on your stock cams) you have to look at one very important thing:
Your exhaust system and exhaust back pressure:
If you have a stock log type exhaust manifold, with a close coupled cat, with a dual cat exhaust system, small exhaust tubing, and a couple of restrictive mufflers on your car then it is possible at peak power to have upto 10psi of back pressure.
If this is the case, my first recommendation would be to upgrade to a high flow, low pressure exhaust system because of the potential power gains; however, I do know that some of our readers have cars that they are setting up for their parents or for dual use where their partner or the laws in their location …etc are really strict when it comes to any added exhaust noise or any aftermarket exhaust. In this case, where exhaust upgrades are not an option, then you must select your camshafts, and tune your cam timing to where you have ABSOLUTLEY the minimum possible amount of overlap. If you have significant overlap, then the more you rise above about 4500 rpms the more your supercharger will suffer and the more power you will waste. If the supercharger is geared to 7psi of boost for example, then during overlap, the cylinder sees 7psi of boost on the intake side, and 10psi of back pressure on the exhaust side, the net result is that air will flow from the high pressure zone (the exhaust) to the lower pressure zone (the intake) and so your cylinder will start to fill with exhaust gases. As the rotation continues, the exhaust valve will close and overlap will end, and the intake valve will stay open for the remainder of the intake stroke (for the rest of the duration of your intake cam), and the rest of the cylinder will fill with fresh air.
What happens here is that we get a cylinder that filled for 30* of overlap with exhaust air, and then filled for another 210* (of the original 240* of duration for a typical street cam) with fresh air. The result is a cylinder that is only 85% filled with fresh air or an engine that is literally 15% smaller in displacement! On the other hand, if our supercharger is geared for 18psi for example, then during overlap we will have 18psi on the intake side and our exhaust back pressure of 10psi on the exhaust side, the net result of this overlap is that our supercharger is effectively only producing 8psi worth of differencial pressure between the intake and the cylinder and so we are only going to get a power boost of 8psi during overlap. So, during those 30* of overlap the supercharger is only effectively porducing 8psi of boost, and after that once the exhaust valve closes, the supercharger will be able to go back to operating at full boost for the other 210*. The net result is something like 16psi of boost so 2psi (or about 12%) of our power was wasted.
Supercharger tuning through cam selection and cam timing
Because of the negative effects of overlap on a supercharger car’s performance, and especially in the case of high exhaust back pressure as is the case with most factory supercharged cars, we find that the optimal cam duration for the intake cam is typically 30-40* of duration less than a normally aspirated camshaft for the same peak power RPM. The decision to reduce the intake cam duration rather than split the duration reduction between the intake and exhaust cams, is that the intake cam will flow air under pressurized conditions (due to the addition of the supercharger and the increase in intake manifold pressure) and so at a reduced intake cam duration the engine will still be able to get it’s full share of intake air. At the same time, the high rpm effeciency improvement from the reduction of overlap will also boost power production with a more conservative cam. Finally, if we would like to get more flow from the intake cam, there is still the option of using a higher lift camshaft (with a steeper profile due to the decreased duration) with supporting valvetrain modifications to make sure valve float doesn’t occur at higher rpms.
Intake cam timing:
The cam timing for the intake cam would ideally be retarded which would move the intake cam opening event farther away from the exhaust valve closing event so as to reduce or eliminate overlap, and as a side effect the power stroke duration will increase by retarding the intake cam which can also compensate for the lost power from the duration reduction.
The exhaust cam duration and lift for a supercharged version of the motor should be similar to a nitrous camshaft, in the sense that the exhaust cams on nitrous specific builds have:
1- Very healthy cam duration & very healthy cam lift to allow a severely elevated amount of exhaust gases to be able to effeciently exit the motor when the nitrous is activated and the horsepower (and thus the exhaust gasses) have both doubled in quantity.
2- As little or no overlap if possible, as any overlap would mean that nitrous would be sprayed from the intake side and out the exhaust, which is wasteful of our limited supply of nitrous. Similarly the more overlap we have, the harder the supercharger will have to work because of what we explained earlier about either exhaust reversion into the intake, or the supercharger pressurizing the exhaust.
Exhaust cam timing:
Advancing the exhaust cam both opens and closes the exhaust valves sooner. Opening the exhaust valve sooner slightly reduces the power stroke, but at the same time it reduces overlap and makes better use of our supercharger. Typically an an advanced exhaust cam combined with retarded intake cam will provide the best results on a supercharged car, especially with a restrictive exhaust.
If we had a high flow exhaust system installed, then it may not be beneficial to advance the exhaust cam, a high flow exaust system that is optimized for our engine’s power requirements can clear the combustion chamber of all it’s gasses very effeciently. Having a high duration exhaust cam, a low back pressure exhaust system and a no overlap what so ever camshaft means that we are giving the exhaust gas plenty of time to exit they cylinder, the intake valve still hasn’t opened (because the we have decide to retard it, or use a conservative cam with less duration) and so the supercharger is not pushing any new fresh air in yet, now the cylinder is void and so some of the exhaust gas can revert back into the cylinder, then the exhaust valve will close, and then the intake valve will open only to find the cylinder already partially filled with exhaust gases.
This isn’t a problem with a restrictive exhaust because a restrictive exhaust will take some time to clear the cylinder at a lower velocity, however with a higher flow exhaust system we must be careful not to dial out ALL of the overlap in the cam timing, or to overcam the exhaust cam (using too much duration).
So exhaust cam timing can be advanced or retarded, depending on the exhaust modifications and the intake cam selection and thus must be dynotuned.
It’s important to note that with all of these changes in cam selection , overlap, power stroke duration, and cam timing, that the power stroke duration is effected and if it is effectively shortened then we may need to retune the car’s timing advance on the dyno (for increased advance) to regain losses in duration of the power stroke (again this against popular thinking of never to advance timing on forced induction cars, if we have a shortened power stroke, or an application with signficant overlap then it may be necessary to do so).
So we see here that the end result here a lop-sided camshaft with a conservative duration, high lift cam on the intake side, and a normal duration, high lift cam on the exhaust with minimal lobe seperation angle and minimal (but not necessarily no) overlap.
The exception to the rule:
Sometimes people take a car that starts off with a 9000 rpm redline, has an 11.5:1 compression ratio, and a 280* duration camshaft, and an aggressive naturally aspirated-esque timing curve and decide to supercharge it for more power. One suck example is kleemann’s kompressor for the SLK55 AMG (which already makes 400 hp in normally aspirated form from an 11:1 compression ratio motor). In this type of application, if you use a more conservative cam, and dial out all the overlap, and increase the power stroke, in combination with an already high 11:1 compression ratio and a healthy amount of boost pressure (7psi or above) you will end up with a motor that produces extremely high peak cylinder pressures and those intense pressures and heat may easily start off a chain reaction of pre-ignition and detonation and you will find that no matter how much you retard the timing that the setup will end up both powerless and still not that safe.
In this case, I would consider RPM and compression my primary power adder, and my supercharger as my secondary power adder (that is unless I decided to change that and went ahead and lowered the compression ratio of the motor). In this case it is ok to sacrifice some supercahrger high rpm effeciency for preventing high-load & low-rpm detonation. Furthermore, to overcome the overlap inherent in this kind of high rpm normally aspirated powerplant it would be very advisable to use a centrifugal supercahrger that is capable of producing more boost and flow with increased rpm rather than a roots type charger that will easily run out of boost and flow capacity (CFM) when facing an aggressive camshaft ‘leaking’ boost away.
Here is a great example of how cam tuning can affect supercharged power:
The car is a 1.8 liter honda motor equipped with:
- Supercharger optimized big pirmaries and short runners Kamakazi header
- A greddy 2.5″ SP2 catback exhaust system.
- An LHT ported “S” supercharger inlet tube
- An LHT ported intake manifold ( Non intercooled)
- A Carbon fibre intake
- A Jackson racing eaton M62 supercharger geared for 7.5-8 psi.
The black line is the baseline run with all of these modifications before tuning.
The blue line is the power acheived after a full tine (camshaft timing redone for reduced overlap, ignition timing re-optimized, and air fuel ratio optimized for peak power).
The red line is the same as previous but running open-header with no exhaust system. Obviously this last run shows that the 2.5″ exhaust is more than adequate for the 250hp power figure.
You can see on this graph that by reducing overlap and properly tuning the car the power peak not only increased by 25 horsepower, but more importantly shifted up by 1000 RPM’s due to increased supercharger high rpm effeciency from reduced overlap.
Taming the Untuneable – OBD2 Engine tuning guide
If you’ve bought a car (or even a motorcycle) in the last 5 years, then chances are that your vehicle is equipped with an LSU4.2 wideband oxygen sensor. This wideband oxygen sensor, unlike old narrowband sensors of late, is able to tell the ECU exactly how much unburnt fuel is running through your exhaust system. Which allows the ECU tighter control over the exact amount of fuel injected into the cylinders both for better economy and for reduced emissions.
The downside of the availability of these sensors is as follows:
When manufacturers didn’t have tight control (or a solid sensor reading) of exhaust gas content, then in order to prevent the engine from running dangerously lean under high demand and damaging the motor, they were forced to default to adding in a margin of safety worth of fuel, running the motor well into the rich range with a healthy dose of fuel per the air ingested.
Now although this richer mixture (and sometimes excessively rich) was bad for emissions and mileage, it did allow cars to have better throttle response, produce smoother wide open throttle acceleration, and respond better to bolt-on modifications.
Now when it comes to power enrichment tuning (for high load and full throttle operation) there are basically two different philosophies :
The Rich Life:
In this philosophy the engine is tuned for a target between 13.5:1 AFR and 11.5:1 AFR depending on the total amount of combustion pressure in the engine (Compression, rod ratio, boost, squish…etc) . With this richer mixture, there is a lot of energy (in the form of fuel) to be harnessed out of the mixture timing is generally advanced to start the combustion early to take advantage of this power rich charge of energy.
Sure some fuel is wasted, but if you wanted to save fuel you wouldn’t be running at full throttle now would you ?
Lean is Mean:
In this philosophy, the engine is tuned for a leaner 14.7:1 AFR to 13.5:1 AFR at full throttle depending on the conditions. As the mixture is leaned out from the power happy theoretical value 12.7:1, the leaner mixture has less fuel cooling and higher combustion pressure, where cylinder pressure builds more rapidly after the initial spark event which gives a more complete and cleaner burn for the air and fuel charge.
However, this hotter burning mixture can spike cylinder pressure too fast, and force us into pre-ignition and pre-ignition caused detonation. So, to compensate, timing advance at full throttle under the lean is mean philosophy is reduced to counter-act the affects of the heat buildup.
Retarding the timing in this manner delays the initiation of the combustion process, which reduces the amount of air and fuel burnt inside the cylinder and increases the amount of air and fuel burnt in the exhaust system. This raises exhaust gas temperatures (EGT’s) which improves the performance of catalytic converters and lowers emissions. However, having a larger portion of the air and fuel charge burning OUTSIDE of the cylinder in the exhaust system means that ultimately we are throwing away energy that could have been harnessed inside the cylinder to produce more power.
How does this affect LSU 4.2 equipped cars:
OEM manufacturers are coming under pressure to produce cleaner and greener vehicles, not just at idle and cruise, but through-out the entire operating range of the engine. Because of this pressure, manufacturers are more commonly opting for the Lean is Mean mantra of tuning, by trading off some performance and power for higher combustion efficiency and better catalyst performance.
The main problem with this mantra is not only in that the car is not tuned for peak power in stock form, but rather that with additional modifications to the engine, the ECU will always try to maintain that same lean mixture holding back further power increases or even lose power with modifications.
How can you lose power with modifications ?
It’s a commonly known fact that combustion pressure increases , the more air and compression you put into your motor. Modifications that help the motor breathe better deliver more air to the combustion chamber which results in higher combustion pressure when the mixture is ignited. This higher pressure increases the speed of flame front propagation more so than it already is accelerated (due to the lean is mean tune) which can cause pressure spikes and pre-ignition / detonation. The ECU will detect this engine knock and severely retard timing to save the motor and with the retarded timing , even more of the combustion process will occur outside of the cylinder, further reducing power.
So with this style ECU it is not only likely that may not gain power with bolt-ons. It is also likely that you will LOSE power with mods, unless you get the car retuned to a richer mixture.
The Other Problem:
The other problem with these ECU’s is that until recently, they were untuneable. With traditional style piggy back fuel and timing controllers, you used to be able to lie to your ECU about the amount of air entering into your engine by intercepting and modifying your air metering signals, which forced the ECU to run a richer or leaner mixture at full throttle depending on how you tuned your controller.
With the newer wideband equipped ECUs; the ECU is able to accurately read the final air to fuel ratio in the exhaust using the wideband oxygen sensor. Now that the ECU knows that you have altered the incoming air metering signals, and now that it has detected that the final air to fuel ratio is not where it was intended from the factory, the ECU applies a correction known as a ‘fuel trim’ to correct the final air to fuel mixture back to where the OEM engineers had set this target to be. By doing this, the ECU cancels out your tuning efforts and returns power levels to stock.
Until very recently, these cars were un-tuneable short of ripping out the entire engine management system and installing a standalone aftermarket system and tuning from scratch. This however is a drastic measure that is not fathomable for anyone with light modifications or even a bolt on supercharger system.
So what is the new concept ?
The new concept in tuning these ECU’s is to use a smart piggy back controller to intercept the Oxygen sensor signal (rather than the air metering signals). These new piggyback controllers allow you to alter the target air to fuel ratio that the ECU is looking for by adjusting the oxygen sensor signal to correspond to the 14.7:1 air to fuel ratio when YOUR DESIRED TARGET mixture is reached. This way, when the oxygen sensor is reporting 12.5:1 AFR to the piggyback, the piggyback will relay that to the ECU as 14.7:1 and the ECU will be happy with what it ‘sees’ and the car will produce the power that we want.
Moreover, now that we have setup this adjustment in the computer’s feedback control system, the ECU will now make adjustments to stay as true as possible to this new target, just as it did to the OEM target even if conditions change. Which means the ECU will re-tune itself to the proper target AS YOU APPLY MORE MODIFICATIONS to always keep you in-tune.
Taming the Untuneable Part 2- OBD2 Engine tuning guide
In part 1 of this engine tuning guide, we explored the difficulties associate with altering the target air to fuel ratio on cars equipped with wide-band oxygen sensors and self learning ECU’s
1- Intercept the Oxygen sensor current or voltage signal (depending on the sensor type) going to the ECU
2- Monitor a set of control signals that tell the piggyback when and If the car goes into a performance state (such as wide open throttle, or a predetermined boost or RPM level)
3- Once car crosses over into this ‘enrichment region’, alter the oxygen sensor signal such that the On Board ECU thinks that the engine is running leaner than required (for example to enrichen up the mixture by 5%, make the ECU think that the current mixture is 5% leaner than the factory target)
4- Over time , the ECU will compensate either directly (through its own feedback control range which is typically +/-15% duty cycle) or through an external fuel controller or piggyback controller to now regulate fuel delivery at a new target air to fuel ratio that is set by our signal interceptor.
5- Check using an external wide-band oxygen sensor (which is separate from the sensor who’s signal is being altered to fool the ECU) that your actual air to fuel ratio is closer to the ideal required air to fuel ratio based on your boost level, compression ratio, rpm, octane level, and timing advance figures.
6- Check using an OBD scanner that your Short Term Fuel Trims (STFT) are now near 0% which means that the ECU is now happy with what it believes the fuel mixture to be and will not make any adjustments from where you are now…. which is … the perfect tune
The three products on the market (and as far as I know, the ONLY three piggy back controllers that work on this type of problem) are:
- The SplitSecond Enricher
- The URD AFR sensor calibrator
- The AEM F/IC O2 Skew function
The split second enricher has the following features:
- Dual Channel Correction which is handy on Boxer 4, V configured engines where every engine bank has its own primary wide-band oxygen sensor.
- External voltage triggered which means you can start altering your oxygen sensor signals based on an external map sensor at a preset pressure level, an external rpm trigger at a certain rpm level, an external MAS sensor once the car goes above a certain flow level or any other combination of external voltages (a nitrous kit arming and activation trigger signal would be a great example).
- In addition to the external trigger option, the enricher has an Internal Pressure Sensor and a voltage adjustment setting that allows you to trigger enrichment based on a preset boost level using all the built in hardware which reduces the cost, installation complexity, and most importantly the probability of failure when having to buy and wire up a second pressure sensor for activation.
- Dual mode operation: Since the enricher is triggered by a certain voltage point (internal or external) the enricher’s functionality is fairly straight forward and basic where you toggle between only two preset air to fuel ratios namely 14.7:1 (stock) and the air to fuel ratio that you set using the adjustment knobs. This works well on lightly modified cars but may not be enough to smooth out boost transitions or part throttle hesitations on certain applications.
- In addition to having two wide-band channels, the enricher has a pair of inputs and outputs to alter the voltage of the downstream narrow-band oxygen sensors positioned after the catalytic converters. These additional adjustment channels can be used to adjust the narrow-band signal to prevent the factory ECU from triggering check engine lights for catalytic converter efficiency (since the ECU can no longer read the correct cat efficiency figures due to the altered primary AFR sensor’s signal under high load).
Underdog racing and development URD has been in the business of modifying Toyota engines for a long time coming now. Their original focus was the 1mzfe engine and related supercharger kit upgrades building on the original TRD (Toyota Racing and Development) supercharger package with additional fuel, more boost, and a better tune. Since then URD has branched out into more platforms, with more fueling options, and more tuning controllers including the URD AFR sensor calibrator and they have a very strong following on in the Toyota SUV market.
The URD AFR sensor calibrator has the following features:
- The unit has a built in programmable enrichment table that can either be pre-programmed by URD for common setups and familiar applications, or connected to their software for a custom program that fits the demands of your engine combination.
- Having a programmable enrichment map rather than a dual setting target AFR (like the SplitSec Enricher); the URD Capable of smoothing out transition enrichment and fixing hesitation problems related to part throttle & part boost conditions as well as altering the target AFR at full throttle and full boost.
- The device comes with dual channel capability similar to the AFR calibrator which works on V configured engines with dual sensors… however it does not have the ability to alter the secondary sensor voltages to prevent possible Check engine lights (for catalytic efficiency error codes) and additional narrow-band sensor simulators or oxygen sensor spacers might be needed on the downstream sensor depending on the exact application.
AEM is Advanced Engine Management, and although their primary claim to fame was the advanced design of their intake systems and dry element air filter (which won the famous filter shootout for maximum flow AND maximum filtration of all the tested elements); they have recently diversified the company into offering a full arsenal of performance equipment including standalone engine management systems, water injection kits, gauges and more..
The AEM F/IC is a piggyback fuel and ignition controller with an expanded feature set that is almost as capable as a standalone engine management system and comes with an O2 skew feature that is our focus today
The O2 Skew feature has the following characteristics:
- The O2 skew has a 16 X 21 (iirc) programmable enrichment table that has different enrichment capabilities with respect to engine load and rpm. Engine load can be mapped to a map sensor, or a flow meter alternatively depending on what your engine primary metering sensor is.
- This programmable table allows for extreme fine tuning of the entire throttle and boost range of the fuel map, all the way from Idle up to full throttle and full boost.
- The O2 skew feature can operate both in current and voltage mode (just as the other two products mentioned here) and also has two channels of adjustment for V configured engines with two AFR sensors.
- In addition to these features, the F/IC has the ability to control your fuel injectors and ignition timing directly has an advantage over the previous two devices…
- On lightly modified cars, using an enricher alone for minor corrections relies on the ECU to fine tune the fuel table which works well for minor corrections, however when the modifications are extensive and the corrections are large, an additional fuel controller is required to deliver the right duty cycle to the injectors to compensate for the OEM tune being so different from the target tune and the AEM F/IC has the built in capability to do this.
- Lying permanently to your ECU using the enricher will eventually reprogram your long term fuel trims (LTFT) to match what the ECU thinks is going on with your motor. If you reset your engine or ECU these trims will disappear and the car will have to relearn your tune from scratch. Since the AEM FIC zeroes out all your fuel trims and relies on your AEM FIC fuel map to deliver the correct fueling (rather than the trims in your factory ECU) then resetting the ECU has no affect on the stability of your tune, no matter how big the corrections.
- You can not only prevent your ECU from going into limp mode or cutting power, but you can further maximize your tune to take full advantage of your modifications with the proper fueling and timing.
- Finally, as far as I know, the FIC does not have the ability to alter secondary O2 channels and an external O2 simulator, voltage drop resistor (500 ohms to 1k ohms depending on the sensor current), or oxygen sensor spacer may be required to correct the richer signal being read by the post-cat sensors to prevent the ECU from throwing catalytic efficiency check engine lights.
Watch this video of the process being performed on the AEM F/IC
All three of these devices are capable of making the modification experience a better and more refined experience on ULEV (ultra low emissions vehicles) and vehicles adhering to more stringent emissions requirements using wide-band primary oxygen sensors.
The choice of which device to go with will vary with the severity of the problem you have from minor corrections at WOT from a basic intake & exhaust install to a major retune for a ground up custom turbocharged application that has a completely differently shaped power curve.
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