In this article of basic efi tuning, we're going to take a look at one of the major sensor values on any modern OBD-2 vehicle, their options for Performance Parts and Car Accessories that modify these values to reproduce changes in the performance of the vehicle.
To begin, we're going to discuss the 2 major air metering devices the engine uses to determine how much fuel to inject at any given moment. These would be the Mass Air Flow (MAF for short) and Manifold Absolute Pressure sensor (Map for short).
To begin with MAF sensors, the most barbaric of the bunch was the vane sensor. In more common terms, this was simply a paddle that set in the intake tract, and correlated how far it moved as the air moved over it and produced a 0-5v (0 volts meaning no air, 5 volts meaning the max the sensor could read) signal that the ecu could use to deterine how much air was coming into the motor. This was also calculated with an Intake Air Temperature sensor (IAT) since it did not actually know the mass of the air coming in, just it's flow rate. While these worked, having a paddle resting in the intake tract produced turbulence further back then desired in the intake tract, as well as moving parts with the possibility of failing. Most modern cars do not employ these anymore, I can't think of one to tell you the truth that I regularly work on, and even so, it would be beneficial and rather easy to find a comparable hot wire MAF to replace it.
The second MAF sensor, and most common in today's higher performance vehicles, is the Hot Wire MAF. This sensor is much more sensitive to actual air density with how it is designed and works. This sensor works by heating a suspended wire inside of the intact tract by a specific voltage. As the wire heats up, resistance is added to the wire which the computer correlates into a mass air flow signal. The more air, or the denser air flowing over the wire, absorbs some of the heat of the wire, thereby lowering it's overall temperature and reducing resistance. Most of these sensors have circuitry in the housing itself to convert the signal to a 0-5v response for the computer, though some manufacturers just read the resistance. On vehicles only looking at resistance, corrosion of the wiring over time can cause severe driveability problems, and is the main reason why most manufacturers moved away from that system.
The third sensor to look at in calculating air flow is the MAP sensor. These are very common in your Chryslers and Hondas, to where as the MAF is seen on Fords and Chevrolets mostly. These sensors, instead of resting in the intake path of the motor, reside on the intake manifold, or routed to a source from the intake manifold. The computer uses this sensor to find out the air pressure of the vehicle, and then other sensors and values to determine the amount of air in the motor. A simple way to describe how a computer looks at this is as follows:
Vehicle is at 7hg of vacuum - Throttle position sensor - 50% - correlation table of 50% load - medium injector duty
or
Vehicle is at 16psi of boost - Throttle position sensor - 100% - correlation table of 100% load - maximum injector duty
or
Vehicle is at 7psi of boost - Throttle position sensor - 45% - correlation table of 50% load - medium injector duty
The correlation tables are basically pre-programmed load grids, which take into account many other sensors as well too, such as ambient air temp, intake air temp, throttle position, throttle inlet pressure and anything else the engineers can think of and throw into them. The figures above are just made up truthfully, so don't repeat them to your friends as an actual cars load tables, but merely a simple explanation of how they work. I couldn't put it into words any better then doing that.
If you're still reading then that's good, you're about to get into what these really mean and how to use them to your advantage. If you feel a wall of text smacked you in the face, then that's also good. Simply put, I can't stand ignorance in the slightest, and if I'm going to give you information on how parts change your car and what to do with them, I want you to understand the impact and exactly how they work. I hate posers, and retards that really have no clue what they're talking about. Now onto the good stuff
Performance Parts
Quite a few car accessories can help you modify these sensors to gain additional horsepower and torque from your vehicle safely. These include some common ones such as Apex'i's S-AFC, S-AFC II, and S-AFC Neo, Greddy e-manage, TurboXS D-tec, and even something as simple as a voltage clamp. They all do the same exact thing, and that's change the voltage signal or resistance that the air metering sensor provides and making the computer THINK there is either less or more air in the motor so that it can adjust it's fuel maps.
The simplest of all Performance Parts, the voltage clamp. A small circuitry to limit maximum voltage on a line, which in our case is the 0-5v sensor signal to the engine or powertrain control module (ECM or PCM depending on vehicle). As an example we'll use a Dodge SRT-4, a highly powerful map sensor based turbocharged 4 banger from the boys at Chrysler's PVO team. Stock the vehicle us a 2.25bar map sensor (bar = 14.5psi roughly), meaning it can read from 29hg of vacuum to about 18psi of boost (with 15psi being the stock target). The computer uses the voltage signal of the map sensor to determine how much pressure or vacuum is in the intake manifold and adjusts fuel to it, obviously giving more fuel for more air being in the chambers then less, to give it an optimal air/fuel ratio. While working on numerous SRT-4's, from the basic car accessories, to the larger performance parts upgrades, one thing has been constant across the board, and that was that these cars are rich, pig rich, and could gain a healthy amount of horsepower by leaning them out.
So as we learned before, the map sensor gives a varied voltage between 0-5v to the computer based on air pressure in the intake manifold. Our main goal is to lean the car out at max boost, to bring it up from it's current 10.2:1 Air/Fuel ratio. Bypassing the vehicle's factory boost control (which also reads off of the MAP sensor) with a simple manual boost controller, and our simple map clamp wired into the map sensor, we can now begin testing the vehicle to find the optimum clamp point for Wide Open Throttle (WOT) under full boost. So, as we begin, prior to adjustments, the car at 15psi is seeing roughly 4.5 volts at the sensor. We're going to decrease this maximum voltage, limiting it's highest value to about 4.1 volts via the map clamp (every car is different, do not use these values without accurately testing the vehicle with an air/fuel monitoring device to find your cars specific values and reactions). Effectively, we have made the computer think that the car is only running 12psi of boost now, so it adds fuel for that, when in reality the car is running at it's 15psi target still. This has had the net result of leaning the vehicle out at max boost, but has changed nothing for it's partial boost regular driving. Most of the times this was good for a solid +10whp on all cars, and a map clamp costs about 30 bucks, or 5 if you make it yourself. Simple changes like this though do have adverse effects on some computer systems, which are described near the end of the article.
This same exact principal works on MAF as well too. Both styles of sensors give the car the same basic information, limit their value, you limit what the computer sees in terms of air being available to the motor.
Other car accessories in this field are just more advanced, and definitely fall into the dedicated performance parts section. Each one is basically an evolution of the simple map clamp, though with the ability to increase the sensor value as well as decrease it across many points in the rpm range.
The Apex'i AFC's are by far the most common of the bunch, and have been in use for years. Again, nothing more then an advanced map clamp, but now it lets you change it across a broader spectrum of the range, and also take into account other values such as throttle position. AFC's have 2 basic maps, low throttle and hi throttle, and then scale in between. Before we get too deep into this one, I really suggest reading my very first lesson if you haven't, Car accessories and performance parts - part 1, the basics of fuel pressure. I'm going to stress again the most important part, if you're adding or removing at least 5% across the entire band, a fuel pressure change is needed more then MAF or MAP adjustment. If your fuel system has been increased so much that you've lowered fuel pressure past acceptable limits, and still pulling fuel, then you my friend need to stop playing with piggybacks and put a real standalone EMS system in the car. Limiting your sensors range is inviting problems in driveability and ultimately your car's computer from being able to adjust correctly to further changes from performance parts and various accessories.
AFC's, and the highly more configurable D-tec and e-manage allow you to smooth out those air/fuel ratio inconsistencies in your vehicles maps. For the novice with a modified fuel system that really needs some tweaking, I actually think the d-tec and e-manage are far more user friendly, though they aren't the most popular or normally people's first pick over the AFC. The AFC was one of the first, easy to use, digital controllers in that performance part segment, and the other car accessories like it have been growing up in it's shadow. One of the main features I personally like about the dtec is it's interface with a gameboy, and the ability to incorporate a wide-band air/fuel sensor into it. All of these parts work off of throttle position and rpm correlation, but the d-tec has a nice interface that makes it easy to find that part of the table, realtime, or afterwards in a log file of the run. Air/fuel dips in a certain area, go back to the log, find the highlighted box in the table, and make your adjustments to it. Very easy, very simple.
As for further walkthroughs you will have to look elsewhere for those. At this point I'm not going to do a step by step tuning guide for each and every piggy-back on the market, but jump into the problems that arrise when you're using these performance parts on most modern vehicles.
Most common problem I run into, especially on my earlier example of the SRT-4, is the fact that some people try to ADD fuel with a piggy-back. This can and cannot work in some circumstances. The main reason why it fails to work, is that most people are trying to add fuel at the top of the sensors value range already. All ECM's and PCM's have a value that is not supposed to be crossed, this is referred to as the limit easily enough. The most common rookie mistake, and one that I fix weekly from competitor shops in the area that don't know better, is taking a car that's slightly lean, but with a smooth fuel curve, and adding 5-10% to the map or maf value. The control module sees this as a problem, and possibly an open short to the 5v line or loss of resistance in the sensor, sets a check engine code, and ultimately puts the car into a 'limp mode' meaning it's running off of a pre-determined map and no longer taking said sensor into account for critical calculations.
Another common problem with increasing fuel is the computer trying to protect itself. When manual control of the boost has been taken over, and you push a value far too high through the air metering sensor, the computer will cut fuel to protect itself. No fuel = no combustion, and highly against what we're trying to accomplish here with tuning the car for more power.
That's not it for problems, oh no, not when using piggybacks. Here's 2 more that people almost never even glance at when installing car accessories and performance parts. Long-term and Short-term fuel trims, and ignition timing. Oh boy lets look at ignition timing first, as this one can be a killer when not monitored.
Vehicles use their air metering devices to calculate load on the motor. When these values are decreased, the engine simply thinks it's not working as hard, and some, but not all decreased injector duty (yay what you wanted to lean the car out) and then raised ignition timing for better combustion and performance at lighter loads. As we get into further articles, you will definitely learn, that as horsepower goes up, timing needs to go down to prevent detonation which will damage pistons and other portions of the rotating assembly on the motor. Many OBD-2 monitoring devices can datalog these crucial values so that you can see the changes as the air metering device has been altered. This is just one more reason that when installing car accessories and performance parts, you should always go back to the most basic adjustment first, fuel pressure and get it as close as possible with just that alone.
We're not done yet though. While not as deadly as the ignition changes to the motor, the short term and long term fuel trim changes can wreak some major havoc as well too. You may THINK you have the perfect tune, but be miles away from it. These 2 values are actually very self explanatory here but I'll do it anyways for somebody not following. The short-term fuel trim monitors the o2 sensors on the vehicle, and make adjustments based on their readings to accomodate for things such as clogged injectors, changes to the fuel system, or anything along those lines. This value alone can add or subtract 25% injector duty in most modern cars. If this value stays in a certain range for long enough, the vehicle then converts some of that to long-term fuel trim, which gives an additional plus or minus 25%. So lets get to an example here to make this easy to follow.
You've just installed your new car accessory, this fancy performance part is letting you make all kinds of changes to your fuel delivery so you're driving around, correctly might I add, with a wideband air/fuel sensor to monitor your changes. After about 20 minutes of driving you feel like you have it, that the tune is finished and you're all set. Here's what 99%, yes I'm saying 99% considering how many cars I've ran into this on never checked, is your STFT and LTFT. When you started your car was extremely rich, so it ran for a bit as you made fuel pressure adjustments and got it close, correctly might I add, then you started working in your AFC while driving some more. This ENTIRE time the car was rich, and the computer knew this and was making adjustments of it's own. It pulled all 25% of your STFT on first startup to get the car to an acceptable level, and then needed more as you tinkered with it, so it started to pull LTFT as well too. By the time you were done, in REALITY, and I'm not making this up, your vehicle pulled 30% of the fuel and you did 5-10%. Don't believe me, I dare you to run the same situation on a fresh tune and not get any STFT and LTFT during it.
Once your tune is complete in your head, you should ALWAYS go back and read the obd-2 data to see where the factory computer is resting at. It is very easy to fix this, and does not take much work other then the fact that there is more time involved. If your car is resting with negative fuel trim values across the driving range, then help it along some by pulling just a tad bit more with your AFC. These values do not react as fast as your performance part does, so you may have to drive for 5-10 minutes to see a change in LTFT, though STFT normally reacts very fast, damn near on the fly. Also remember that STFT is taking into account LTFT already, so if you see STFT at 0, but your LTFT is at -20%, the car is still pulling -20% at that point, the short-term just doesn't feel the need to do anymore adjustment.
Ideally when all is said and done, your LTFT and STFT should be within +/- 5% of 0, and your new performance part should only be pulling at max 10% in some areas, and not across the entire band. If you're obviously out of this value range, regardless of how good you think you are, something was done wrong. Sometimes it isn't necessarily the tuning, but certain performance parts just don't work with the application as well as other accessories do (i.e a larger set of fuel injectors, higher flow fuel pump, rising rate fuel pressure regulator compared to static). All those items can drastically alter the fuel curve in the vehicle, and if not matched properly, is very hard to overcome.
If you're still a dedicated reader from part 1, you'll notice I said piggyback systems suck, and that's mainly because of the misinformation floating around about what they can and cannot do. In the grand scheme of things, for lightly modified cars, they can do wonders, and even if you use one yourself on a modern efi vehicle, trying to avoid cockiness here, I'm sure 95% of you never even knew to look at these other values and just assumed all was good. Another reason why I don't put all faith into them as that they're limited, and some cars just can't use them as they pull from too many different sensors and revert changes you make (or adapt, however you want to look at it).
Again, use the comments section to let me hear your stories, nightmares, or triumphs with these systems, or if you found this article helpful and informative, even if it is a long read.
In part 3 of Car Accessories and Performance Parts, I want to touch on some of the myths of various power adders. What they can and cannot do for your car, I'm even going to break into some of the ebay power chips, how some of them really can benefit you in the power department, but why to still avoid them with the real facts as to how they work.
Wednesday, August 13, 2008
Monday, August 11, 2008
Tuning your car for performance - The basics
I'm going to start this lesson on car performance with a quick basic rundown on some of the terms that will be used and their application.
Imports as they are commonly referred to do not indicate simply cars from overseas manufacturers. In the larger sense, the industry sees them as all sport compact and foreign vehicles. This means that for all intensive purposes, it includes cars such as the Dodge SRT-4 (both neon and caliber platform), Chevrolet cobalt, Saturn Ion, Saturn Sky, Pontiac Solstice, Ford Focus and Fusion, and various other makes and models. In a larger sense, Dodge is now considered an import company since most vehicles are manufactured overseas and foreign hands hold a large chunk of the company these days. On the other hand, Toyota is now seen as an American manufacturer since they have put a huge effort into getting their stateside operations going (and one reason why they are also now allowed to race in Nascar).
Tuning, as most would say, is getting the most available horsepower and torque out of a vehicle for it's intended purpose. Whether this may be drag racing, drifting, scca racing or rallycross, most people do not look into the future and think of things such as reliability, repeatability and dependability. Gathering 4-5 extra wheel horsepower out of a car is nice and all, but doing it at the expense of the motor 45,000 miles earlier isn't very productive for most novices.
Performance, in it's basic sense, is how a vehicle performs over a certain course. This may include items such as elapsed time, top speed, cornering g's, braking and acceleration.
Import tuning and related performance parts and accessories has been a growing trend for the past 15 years, and has really boomed as of late. Though the industry is hurting with giants such as Nopi suspending operations for the 2008 season, the passion that drives these enthusiasts hasn't changed for 50 years. I know what you're thinking, I just said it hasn't changed for 50 years, but that this has only been going on for about 15. Present day import tuners are nothing more then the hot rod builders of the days of old. Sure those guys were the forefathers, they're definitely still around, hell my father is one of them with his 1932 Ford 3 window hi-boy. Fact of the matter is, in their youth, they took cheap, inexpensive, preferably lightest cars they could find and throw as much power into them as they could. Sounds familiar doesn't it? Same thing you're doing. Before it was a Chevy Nova having a 454 big block crammed into it, now it's a Honda Civic taking the B20 block from a C-RV, the b18 cylinder head from an Integra GS-R, and various other models parts. Funny part is both cars are running low 13's to high 12's down the track. We have an advantage, and that's the technology that is available to our newer cars, and using that to pull unheard of power levels out of smaller displacement engines. I for one believe there is a replacement for displacement, and that's boost, juice, and rpm's. Sure the same power adders on a larger motor will still make more power, but with those, the import tuning culture has produced some incredibly amazing cars, and an amazing accessory and performance part line-up tailored to it.
So, now that we have the defined terms for my articles, we can now dive further into them and figure out what really makes these things tick and maximize your car's performance.
Import tuning's most basic fundamental hasn't changed from the good old days. Fuel Pressure. Having control of the fuel pressure on a vehicle is one of the most fundamental keys to any succesful setup on a modified import or sport compact. Stock fuel systems in cars these days are amazing. Direct fuel injection, returnless, ability to calculate injector duty based on various sensors around the motor to reduce emissions, increase driveability, and increase fuel economy. This system is great for stock cars as they can rely on the vehicles engineer to give them a trouble free map that accounts for everything that car goes through stock.... STOCK being the key word.
As you get into more modifications on your performance car, the need to modify the fuel trims increases more. Most piggy-back systems (apex-i AFC, greddy e-manage, HKS V-afr) simply modify either the mass air flow signal or manifold absolute pressure signal (map), and some cars such as the Mazda 3 utilize both. A simple and very effective tool to see where the fuel tables need to be overall is a wide-band o2 sensor. These are far more accurate then conventional narrow-band o2 sensors, and can display your air/fuel ratio across your entire RPM band. My favorites are innovate products, they're simple to use, cost effective, and highly accurate with repeatable results from car to car. These don't do anything to directly give you power, and are simply a tuning device for any vehicle and give you feedback on the performance of the car. Anybody making changes to a vehicles fuel map should have one of these or at least be on a REAL (god damnit I mean real, not a dynojet) Dyno. I'll touch on my hatred for dynojet in an article later, just avoid them.
But back to the fuel pressure. As the most basic and fundamental import tuning point on the vehicle, it is critical to get this correct before any other adjustments are made. Fuel injector flow is based off of a fixed pressure value of a standard viscosity fluid. Some manufacturers rate them differently, but the most common rating for the aftermarket is 43psi, while some vehicle manufacturers rate them much higher. The reason this is important is because the base fuel pressure behind the injector itself will increase it's basic flow rate. A 550cc injector running at 34psi at the rail is putting out far less fuel then a 550cc injector running at 52psi at the rail.
After doing a few pulls with your vehicle, take a look at your overall air/fuel ratio for the duration of your run. If you've reduced the backpressure of your exhaust, opened up your intake air flow, or basically anything to increase the performance and VE (volumetric efficiency) of the motor, the motor will be leaner (Air/fuel ratio is higher then before) then when you started. If there is a noticeable deficiency overall in the ratio, then simple fuel pressure adjustments can fix that. At cruising speeds, the air/fuel should always be 14.7:1, an all-motor car under full load should be about 13.5:1, and a forced induction car under full load should aim for 11.2-11.9:1. The higher the number, the leaner (less fuel) the car is. To raise your numbers to hit the ideal points, decrease fuel pressure, and if you're lean and need to lower the air/fuel ratio, increase fuel pressure.
Depending on your car, you may not see a change, but this is where the twist comes in with all that new fangled technology we deal with compared to our fathers. Modern EFI systems also use LTFT (long term fuel trim) and STFT (short term fuel trim) as values in their table to adjust for changes in the motor. In the beginning they're not much of an issue, but if you don't keep an eye on them as you progress into modifying the vehicle they can severely bite you in the ass down the road and hinder performance.
Most vehicles produced today will let either value increase or decrease by about 25%. Most also are not extremely happy about the change either, and certain side effects such as timing changes, reduced throttle on cars with electronic throttle bodies, and also fuel cuts and limp modes can arrise. This is where that fundamental fuel pressure change really comes into play.
After datalogging your car for a bit with any obd-2 software, you will clearly see where these values are for your tables. Your air/fuel ratio might be spot on for your motor, but if you're trims are already 15%-20% out you're going to be in trouble with a few more performance additions. Make adjustments slowly to fuel pressure, about 1-2psi at a time, and give the car a half hour of driving under normal conditions. Recheck your values and ultimately get them within +/- 5%. This simple change has worked with your computer instead of against it, letting it stay within it's optimal maps and still giving plenty of overhead for changes due to weather, altitude, or anything along those lines. Believe me when I say when it comes to import tuning, understanding this one little concept can save you tons of headaches down the road, and is very important to even the most mildly modified cars.
In my next article on car performance, I plan to touch base on piggy back systems and their effects on MAF and MAP sensors. I'd also love to hear from you on your own adventures with modern sport compacts, problems you've run into and conquered or just simply need help with.
Stay tuned for Tuning your car for performance part 2 - piggy-backs and why they suck.
Imports as they are commonly referred to do not indicate simply cars from overseas manufacturers. In the larger sense, the industry sees them as all sport compact and foreign vehicles. This means that for all intensive purposes, it includes cars such as the Dodge SRT-4 (both neon and caliber platform), Chevrolet cobalt, Saturn Ion, Saturn Sky, Pontiac Solstice, Ford Focus and Fusion, and various other makes and models. In a larger sense, Dodge is now considered an import company since most vehicles are manufactured overseas and foreign hands hold a large chunk of the company these days. On the other hand, Toyota is now seen as an American manufacturer since they have put a huge effort into getting their stateside operations going (and one reason why they are also now allowed to race in Nascar).
Tuning, as most would say, is getting the most available horsepower and torque out of a vehicle for it's intended purpose. Whether this may be drag racing, drifting, scca racing or rallycross, most people do not look into the future and think of things such as reliability, repeatability and dependability. Gathering 4-5 extra wheel horsepower out of a car is nice and all, but doing it at the expense of the motor 45,000 miles earlier isn't very productive for most novices.
Performance, in it's basic sense, is how a vehicle performs over a certain course. This may include items such as elapsed time, top speed, cornering g's, braking and acceleration.
Import tuning and related performance parts and accessories has been a growing trend for the past 15 years, and has really boomed as of late. Though the industry is hurting with giants such as Nopi suspending operations for the 2008 season, the passion that drives these enthusiasts hasn't changed for 50 years. I know what you're thinking, I just said it hasn't changed for 50 years, but that this has only been going on for about 15. Present day import tuners are nothing more then the hot rod builders of the days of old. Sure those guys were the forefathers, they're definitely still around, hell my father is one of them with his 1932 Ford 3 window hi-boy. Fact of the matter is, in their youth, they took cheap, inexpensive, preferably lightest cars they could find and throw as much power into them as they could. Sounds familiar doesn't it? Same thing you're doing. Before it was a Chevy Nova having a 454 big block crammed into it, now it's a Honda Civic taking the B20 block from a C-RV, the b18 cylinder head from an Integra GS-R, and various other models parts. Funny part is both cars are running low 13's to high 12's down the track. We have an advantage, and that's the technology that is available to our newer cars, and using that to pull unheard of power levels out of smaller displacement engines. I for one believe there is a replacement for displacement, and that's boost, juice, and rpm's. Sure the same power adders on a larger motor will still make more power, but with those, the import tuning culture has produced some incredibly amazing cars, and an amazing accessory and performance part line-up tailored to it.
So, now that we have the defined terms for my articles, we can now dive further into them and figure out what really makes these things tick and maximize your car's performance.
Import tuning's most basic fundamental hasn't changed from the good old days. Fuel Pressure. Having control of the fuel pressure on a vehicle is one of the most fundamental keys to any succesful setup on a modified import or sport compact. Stock fuel systems in cars these days are amazing. Direct fuel injection, returnless, ability to calculate injector duty based on various sensors around the motor to reduce emissions, increase driveability, and increase fuel economy. This system is great for stock cars as they can rely on the vehicles engineer to give them a trouble free map that accounts for everything that car goes through stock.... STOCK being the key word.
As you get into more modifications on your performance car, the need to modify the fuel trims increases more. Most piggy-back systems (apex-i AFC, greddy e-manage, HKS V-afr) simply modify either the mass air flow signal or manifold absolute pressure signal (map), and some cars such as the Mazda 3 utilize both. A simple and very effective tool to see where the fuel tables need to be overall is a wide-band o2 sensor. These are far more accurate then conventional narrow-band o2 sensors, and can display your air/fuel ratio across your entire RPM band. My favorites are innovate products, they're simple to use, cost effective, and highly accurate with repeatable results from car to car. These don't do anything to directly give you power, and are simply a tuning device for any vehicle and give you feedback on the performance of the car. Anybody making changes to a vehicles fuel map should have one of these or at least be on a REAL (god damnit I mean real, not a dynojet) Dyno. I'll touch on my hatred for dynojet in an article later, just avoid them.
But back to the fuel pressure. As the most basic and fundamental import tuning point on the vehicle, it is critical to get this correct before any other adjustments are made. Fuel injector flow is based off of a fixed pressure value of a standard viscosity fluid. Some manufacturers rate them differently, but the most common rating for the aftermarket is 43psi, while some vehicle manufacturers rate them much higher. The reason this is important is because the base fuel pressure behind the injector itself will increase it's basic flow rate. A 550cc injector running at 34psi at the rail is putting out far less fuel then a 550cc injector running at 52psi at the rail.
After doing a few pulls with your vehicle, take a look at your overall air/fuel ratio for the duration of your run. If you've reduced the backpressure of your exhaust, opened up your intake air flow, or basically anything to increase the performance and VE (volumetric efficiency) of the motor, the motor will be leaner (Air/fuel ratio is higher then before) then when you started. If there is a noticeable deficiency overall in the ratio, then simple fuel pressure adjustments can fix that. At cruising speeds, the air/fuel should always be 14.7:1, an all-motor car under full load should be about 13.5:1, and a forced induction car under full load should aim for 11.2-11.9:1. The higher the number, the leaner (less fuel) the car is. To raise your numbers to hit the ideal points, decrease fuel pressure, and if you're lean and need to lower the air/fuel ratio, increase fuel pressure.
Depending on your car, you may not see a change, but this is where the twist comes in with all that new fangled technology we deal with compared to our fathers. Modern EFI systems also use LTFT (long term fuel trim) and STFT (short term fuel trim) as values in their table to adjust for changes in the motor. In the beginning they're not much of an issue, but if you don't keep an eye on them as you progress into modifying the vehicle they can severely bite you in the ass down the road and hinder performance.
Most vehicles produced today will let either value increase or decrease by about 25%. Most also are not extremely happy about the change either, and certain side effects such as timing changes, reduced throttle on cars with electronic throttle bodies, and also fuel cuts and limp modes can arrise. This is where that fundamental fuel pressure change really comes into play.
After datalogging your car for a bit with any obd-2 software, you will clearly see where these values are for your tables. Your air/fuel ratio might be spot on for your motor, but if you're trims are already 15%-20% out you're going to be in trouble with a few more performance additions. Make adjustments slowly to fuel pressure, about 1-2psi at a time, and give the car a half hour of driving under normal conditions. Recheck your values and ultimately get them within +/- 5%. This simple change has worked with your computer instead of against it, letting it stay within it's optimal maps and still giving plenty of overhead for changes due to weather, altitude, or anything along those lines. Believe me when I say when it comes to import tuning, understanding this one little concept can save you tons of headaches down the road, and is very important to even the most mildly modified cars.
In my next article on car performance, I plan to touch base on piggy back systems and their effects on MAF and MAP sensors. I'd also love to hear from you on your own adventures with modern sport compacts, problems you've run into and conquered or just simply need help with.
Stay tuned for Tuning your car for performance part 2 - piggy-backs and why they suck.
Import tuning and maximizing performance... the good life
So you've got it made. Or so you think... 25 years old, married, bought a house, doing your dream job, tuning imports day in and day out. Making $750/week and everybody that's older then you says damn you're doing good. That is until you figure in your $1650/mo mortgage, $375/mo truck payment, $220 credit line payment, about $600 in credit card bills, you inherited another $30,000 in debt from you wife's school bills and previous credit cards, and on top of it all, $100 for cable and $125 for utilities. You're behind on basically every bill you have and you just seem to wonder where the money can come from.
Yes, that's my life. It's depressing, but in the same uplifting. At one moment it piles you into the ground near the point of desperation, and the very next, makes you extremely grateful for everything that you do have.
I mean, at least I was able to get this far. I've gotten a taste of the American dream, what everybody wants to have. I'm certainly not wealthy beyond imagination, but everything I have is special, and everything I've done in the past 2 years of my life has at least had purpose. Where once I was happy throwing a few thousand dollars into my car, I'm now perfectly content to eat $.25 noodles 3 times a day to keep my food costs down. I've sold my race car, looking to get rid of my truck as it's horrible on gas, yet looking forward to putting a completely paid for, liability only on insurance low budget Nissan or something on the road. It won't be flashy, it won't be a record setter, but it will be one of the few things I can call my own and not the banks.
My life has had twists, success brought me friendships, and when it failed, I lost them. Not because it was a mixing business with friendship type deal, but I myself failed and walked away from them humiliated. I could not face them with what had happened, no way out, no way to fix it. They knew the situation, but ultimately, I had deserted them.
I still live my passion through my work. I get to wake up every day and go into work happy. I work at a very small shop, only 4 employees, where I am the shop manager and lead technician all at the same time. The economy has hurt us, Import tuning and modification has slowed, but unlike much of our competition, we're not folding and still making a profit. There's plenty of frustrations, which you will read quite a bit about in posts to come.
This will probably be quite an unusual blog in the months and years to come. There will be plenty of days that you may read about me ranting on life's more important matters, and others where I am just sharing knowledge on tuning imports from basic EFI fundamentals to forced induction and other car performance setups. I really don't know where this will all end up on the internet, but hell, if it helps one person in life then it was worthwhile. I know I'm not alone in these deals, but I will make it through them, and hopefully my writings and rants will help others with it as well.
Yes, that's my life. It's depressing, but in the same uplifting. At one moment it piles you into the ground near the point of desperation, and the very next, makes you extremely grateful for everything that you do have.
I mean, at least I was able to get this far. I've gotten a taste of the American dream, what everybody wants to have. I'm certainly not wealthy beyond imagination, but everything I have is special, and everything I've done in the past 2 years of my life has at least had purpose. Where once I was happy throwing a few thousand dollars into my car, I'm now perfectly content to eat $.25 noodles 3 times a day to keep my food costs down. I've sold my race car, looking to get rid of my truck as it's horrible on gas, yet looking forward to putting a completely paid for, liability only on insurance low budget Nissan or something on the road. It won't be flashy, it won't be a record setter, but it will be one of the few things I can call my own and not the banks.
My life has had twists, success brought me friendships, and when it failed, I lost them. Not because it was a mixing business with friendship type deal, but I myself failed and walked away from them humiliated. I could not face them with what had happened, no way out, no way to fix it. They knew the situation, but ultimately, I had deserted them.
I still live my passion through my work. I get to wake up every day and go into work happy. I work at a very small shop, only 4 employees, where I am the shop manager and lead technician all at the same time. The economy has hurt us, Import tuning and modification has slowed, but unlike much of our competition, we're not folding and still making a profit. There's plenty of frustrations, which you will read quite a bit about in posts to come.
This will probably be quite an unusual blog in the months and years to come. There will be plenty of days that you may read about me ranting on life's more important matters, and others where I am just sharing knowledge on tuning imports from basic EFI fundamentals to forced induction and other car performance setups. I really don't know where this will all end up on the internet, but hell, if it helps one person in life then it was worthwhile. I know I'm not alone in these deals, but I will make it through them, and hopefully my writings and rants will help others with it as well.
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