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Shaggy
 Post subject: GTX Fuel Cut System
PostPosted: Fri Sep 14, 2007 12:06 am 
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Found this tonight, well long but well worth a read




The Fuel Cut System
If you have ever experienced a very sudden drop in power while pushing your 323 Turbo really hard, almost like your car is 'bucking' back, you have likely encountered the factory fuel-cut system. Although there is normally a buzzer which sounds just before the fuel-cut engages at approximately 10.7psi boost pressure (some cars a little higher, some a little lower) there is a chance that a previous owner has disconnected it.

Why did Mazda include a fuel-cut system in 323 GTX and 323 GT ?
A very good question, indeed. In short it is there to prevent you, and Mazda in the case of warranty claims, from incurring huge repair bills replacing engine components damaged as the air/fuel mixture leans out and combustion temperatures soar. The factory fuel map, you see, does not maintain the proper air/fuel ratio above 11psi. At air flow levels above that, the ECU simply injects enough fuel for 11psi of air pressure and that's it. Remember, the car came preset from the factory running just 7psi of boost. Although Mazda's design team came up with an adequate ECU program for standard street use, once you begin modifying the car you get into this lean zone very quickly.

Why is my car hitting this boost cut ?
Normally, the excessive boost which triggers the fuel cut develops from one of 2 areas: either you are experiencing 'boost creep', a phenomenen in which the flow resistance of the turbocharger's turbine becomes lower than that of the turbocharger's wastegate, or else your car's breathing abilities have been improved enough to "fool" the factory wastegate into thinking you are running less boost than you actually are.

In the first scenario the excess exhaust gas that normally bypasses the turbocharger turbine finds a lower restriction exit through the turbine itself. This spins the turbine faster developing yet more boost pressure. In the second case, a very low restriction intake and exhaust system increases the pressure differential the exhaust gas flow sees across the turbocharger turbine when compared to the stock configuration. This has the effect of 'overspinning' the turbocharger before the wastegate can properly control the amount of boost. Both of these situations will be magnified on cold days -- when the denisity of the air being drawn into the engine is increased. These problems usually occur after removing the car's catalytic converter. So, here we find one answer: re-install any removed cat converters, or introduce sufficient back pressure to prevent boost from building that fast. Unfortunately, this undermines the goal of increased engine performance. In addition it can also affect the longevity of the engine, turbocharger, and exhaust manifold as the presence of the catalytic converter raises EGT's by about 200-300 degrees due to the significant back pressure they ad to the exhaust system.

Should I try to 'defeat' this automatic fuel cut ?
Well, the worst thing you can do is just remove or disconnect it -- unless you have taken steps to add the appropriate amount of additional fuel at elevated boost levels. When you consider that a 323 Turbo running 15psi of turbo boost and the correct air fuel ratio will develop an exhaust gas temerpature (EGT's) of 1,400-1,500 degrees Farenheit, you can see just how important regulation of air/fuel ratio is. At 1,400-1,500 degrees, the engine is already under enough thermal stress. When lean conditions prevail, combustion temperatures will soar -- upwards of 2,000 degrees -- causing pre-ignition of the incoming air/fuel mixture, detonation and thermal stress fracturing of the cylinder head. Typical casualties of frequent excursions into 'the lean zone' are burned exhaust valves, damaged valve seats, pistons with holes in them, and warped or cracked cylinder heads. The safest course is to leave the boost-cut functioning normally until you have installed an upgraded ECU, or a suplemental fueling system ofsome sort.

How can I deal with boost creep problems ?
Boost creep problems can be mild or severe. In a car which creeps to 12-13psi the easiest solution is normally to install an upgraded ECU, which will allow the engine to run with the proper fueling at these boost levels. However, boost creep that runs past the limit of the factory turbocharger and fuel system (16psi) can be much more serious. Boost creep is normally cured by installing an upgraded front pipe, one which not only has higher flow capacity from being much larger in diameter, but also provides a separate low restriction exhaust route for the turbocharger's wastegate flow which allows the wastegate to react faster, helping it control runaway turbo boost. Furthermore, to avoid degrading performance the secondary exhaust line for the wastegate needs to blend back into the main front pipe after the flame front has extinguished -- and that means at least 18 inches from the turbocharger outlet itself. Although there are some front pipe offerings on the market currently, they are all "hack" jobs which replace the short right-angle turbo outlet itself. These pipes do not help control boost creep and can actually degrade performance as they integrate the wastegate exhaust stream back into the main line in the middle of the flame front -- and this can severely disturb combustion and exhaust scavenging. Reich Racing is currently track-testing a high-performance front pipe replacement that replaces everything from the turbocharger right back to the cat-converter.

How can I run higher boost levels safely ?
As for people looking to run more than 11 psi of turbo boost safely there are basically 2 options. Both involve supplying some means of controlled enrichment of the air/fuel ratio above 11psi. This can be done either by adding a supplemental fuel computer, like the HKS PFC F-CON, or by installing the upgraded ECU we have developed. HKS's F-CON works by modifying the pulses the factory ECU sends to the injectors after taking readings off it's own MAP sensor and calculating the correct amount of fuel required. The downside here is that a PFC-FCON, complete with harness and installation kit, sells for over US$1,200. More importantly, HKS's long term support of this product is questionable. A more cost-effective alternative, at US$275, is our upgraded ECU, which modifies the fueling map to 1) remove a dangerous part throttle lean condition that occurs around 10psi of boost with the stock ECU; and 2) Provide a fuel map which extends up to 16psi. In addition, our ECU upgrade maintains all the factory diagnostic codes and testing procedures and does not utilize an external MAP sensor which can fail without warning or notice. The ECU upgrade for the 323 turbo is available in 2 configurations: The High Performance Spec variant is programmed to take advantage of a lower restriction exhaust and a higher flowing open-element type air cleaners while providing a fuel MAP which extends up to 16psi. For pure competition vehicles, where fuel mileage is not a concern and the exhaust system may simply consist of a straight pipe, the ultimate in response and power is needed. For that we have the Race Specvariant. Purchasing an uprated ECU is simple. You can either send us your ECU for upgrade, or else purchase an uprated ECU from our stock and then send us your stock ECU back. Please contact us for extreme competition applications involving larger fuel injectors and uprated fuel pumps.


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Why upgrade my ECU ?
Upgrading your ECU provides a low-cost solution to engine fueling problems caused by the stock ECU's programing, which runs the engine very lean at anything over 11psi of boost. Contrary to what others might tell you, all ECU upgrades are NOT created equal. Sometimes referred to as "new-tech tuning", reprogramming an ECU requires in depth knowledge of just how your engine management system works. Unlike the "other" 323 shops, Reich Racing is the only one who develops and sells their own ECU upgrades. Maintaining this kind of control enables us to be sure our customers are getting what they pay for, and allows us to customize upgrades by independantly setting controls like the rev limiter. Mazda made these cars with no less than 4 different ECUs -- and, unlike the others, we can upgrade all of them -- even EURO and Japanese-spec ECUs. ECU upgrading is a complex business and the people upgrading your ECU better know what they are doing. If a 'revision C' upgrade makes it's way into a 'revision A' ECU you've got problems. Unless the shop has developed upgrades for all these ECUs you run the risk of getting an incorrect upgrade installled, which will not work properly in your car and could casue serious damage.

Are all ECU upgrades created equal ?
Absolutely Not !! The Reich Racing ECU upgrade is the only one that addresses a part-throttle lean condition present in the factory computer at around 10psi. While this is not a huge problem for performance or longevity, we figure if you are going to do a job - do it right. The added time it took to fix this problem was minimal. Reich Racing prides ourselves on developing the best ECU upgrades as well as giving you the best value for your money. This can only be achieved once you fully understand the problems that exist in the stock ECU, and differences that exist revision to revision.

Some guy told me he would sell me a copy of a chip for less than a Reich upgrade sells for - should I go for it?

Well there are a number of concerns here: are you actually getting a real ECU upgrade ? Is it a quality upgrade ? Is it the correct upgade for my ECU ? If it is not the correct upgrade who will pay for a new engine when mine gets wrecked ? Lastly there is the issue of software piracy. The upgrade code is owned by the company the develops it. Any kind of copying or duplication is plain and simply theft. Selling ECU upgrades is one of the ways we make money - and as long as we make money we stay in business to sell you parts that not only help your 323's go faster, but also help keep them on the road affordably. In the past Reich Racing has not made a big issue out of the copyright issue as, more often than not, someone buying a hack job gets what they pay for. Even though it is not a prevalent problem, we have made thousands of dollars selling people used engines and cylinder heads to replace ones damaged from incorrectly upgraded computers.

What is an 'ECU' and what does it do anyways ?
In short, the ECU - which is short for Engine Control Unit - does just that. It controls the amount of fuel the engine gets, the timing of the fuel injections, and the timing of the spark. It also has a hand in adjusting the idle speed when the engine is cold, or heavily loaded. It also makes adjustments to the air/fuel mixture depending on the elevation you are driving the car at (air density changes with height above sea level), the prevailing engine temperature, and temperature of the intake air. In short, it does alot. It is this sophistication which allows electronic fuel-injection cars to generate more Horsepower and run more efficiently than their carburated counterparts.

Factory Turbo system: information, limits, & upgrades
Much like the factory fuel system, the stock turbocharger runs out of juice at anything above 15 or 16 psi. If you push it beyond this, expect dramatically elevated levels of bearing wear as the turbo over spins trying to keep up. If we appeal to the basic laws of thermodynamics, we can also see that as the stock turbo is pressed beyond it's performance envelope it will impart more and more heat into the incoming intake air. In fact, at 7.5 psi of boost with an ambient air temperature of about 90 degrees Fahrenheit the stock turbochargers' outlet temperature is around 225 degrees F. At 15 psi this figure increases to 290 degrees and at 20 psi skyrockets to almost 400 degrees (note: we are not reccomending running at 20 psi with the stock turbo - this number is just given for a comparison). As intake air density decreases with increasing intake temperature, so does the amount of power you are generating. The stock intercooler is barely up to the job of cooling an 8 psi intake charge little lone the dramatic increase in heat seen at these elevated boost levels. In addition, the increased temperatures impart more thermal stress on the engine and increase the chance of pre-ignition based detonation -- a recipe for a very large repair bill indeed.

How do you run elevated boost levels ?
Well, for starters you need to ensure ou have the correct fueling ratios to run past the stock boost cut at 10psi. As the factory ecu will not do this on it's own, you need to use a form of fuel enrichment, like our ECU upgrade. Running big boost without this is a recipe for disaster. Now, with that taken care of, using a hi-flow intake (one that removes the highly restrictive factory airbox and replaces it with an open element air filter), and a hi-flowing exhaust system will allow the engine to breathe better and results in a change of the pressure differential across the engine itself. This, in turn, 'fools' the wastegate into allowing the car to run more boost pressure than the factory setting. There is an upper limit to this gain, however. these mods normally won't get you past the 10.5-11psi mark. After that, we need to install some kind of boost controller to enable further increases. Although there are mechanical boost control valves available they are far from ideal. They do not give a stable boost curve and are not very convenient, requiring you to pull over and adjust them under the hood when setting the car up. This gets frustrating when you need to keep re-calibrating it as the seasons, and therefore average ambient temperatures, change. Although some customers have installed manual controls inside their car, the additional vaccuum line length that needs to be run can increase turbo lag substantially. When we say 'Turbo lag' we are referring to the amount of time it takes a turbocharger to go from generating a low level of boost to a higher rate of boost. In essence we are talking about the rate of turbocharger acceleration here. With all their inherent compromises and limits we do not reccomend these.

Instead, we reccomend the use of an electronic boost controller. These have many benefits when compared to manual boost controllers: a much more stable boost curve, convenient cockpit adjustment, lockouts to prevent passengers from playing with your presets, and - most important of all - FASTER turbo spool up. Electronic boost controllers function by intercepting and regulating the signal sent to the turbocharger's wastegate. A turbocharger wastegate is quite a simple device, really. A pressurized line from the intake manifold is run to a standard pressure diaphram which in turn pushes a rod that opens the wastegate to relieve excess exhaust flow. The problem is that a diaphram works in a quasi-linear fashion. The best that can be hoped for is one with logarithmic actuation. In a nutshell this means even a small amount of boost pressure will begin to force open the wastegate -- and this allows exhaust gases to exit without spinning the exhaust turbine faster, meaning slower boost buildup than the ideal situation. An electronic boost controller, however keeps the wastegate from seeing ANY pressure until it has almost attained maximum boost. In this way the turbocharger builds boost much faster - and that means running more boost at all lower RPM levels. That means more power and torque down low to help the engine accelerate faster into it's powerband. Although it is a difficult concept for alot of people to grasp, a car with excellent road traction, like the 4WD GTX, that has, say, a flat 165HP and 165lb-ft of torque from 2,000RPM to 7,000RPM will accelerate faster than a car like an Integra R which, even though it has 195HP, develops all it's power above 5,000RPM and has next to no torque (at any engine speed!). Top speed is another issue though. Once time is removed from the equation then it is solely engine HP and it's mechanical advantage (gearing) up against mechanical losses, mechanical drag, and aerodynamic drag -- in this situation, with similar drag values, the car with the higher horsepower will allways win -- but it is not often one finds themselves in a battle for top speed supremecy. Besides, the differences we are talking about here are well into the 120+ MPH range, meaning they are not really relevant for street-driven cars. In other words, you can make your 323 turbo accelerate faster by increasing it's low-rpm power as well as it's high RPM power. An electronic boost controller helps you do both.

Turbocharger upgrades and replacements
Now, if your 323 turbo is driven at 15-16psi levels for extended periods of time, or if you have the desire to go beyond 16psi, then it's time to look at upgrading the stock turbocharger. At 16psi the stock turbocharger is at the very outside of it's performance envelope. When delivering this amount of airflow it is not operating as efficienctly as either our upgraded turbocharger or our VJ-16 turbo replacement. Improved efficiency means these turbochargers heat the air less at that airflow level - meaning a cooler intake charge -- and that means more horsepower. As to whether an upgrade or replacement would suit you better that depends on useage. For sustained 15-16psi boost levels with occasional excursions to 18psi our turocharger upgrade is the best way to go. With only a minimal increase in turbo lag it extends the upper end of the performance envelope about 2 psi. With this turbo set-up you can run at 16psi for extended periods with no accelerated turbo wear. Pushing 18psi of boost it still heats the air less than the factory turbocharger does at 16psi. Our upgraded turbochargers are completely overhauled and professionally balanced. Rebuilt units are fully bead-blasted, have new bearings and seals installed, and have both the compressor wheel and housing upgraded. Basically it finishes the process as a new turbocharger. Our VJ-16 turbocharger, on the other hand, is a complete turbocharger replacement for even more demanding applications. If you need to constantly run in the 18psi range with excursions to 21psi then this is the turbocharger for you. Although it does have more turbo lag than the stock turbocharger (this can't be avoided as turbo size increases) this can be minimized with the use of an electronic boost controller. At 21psi the outlet temperatures on a VJ-16 are comparable to that of the stock VJ-14 turbocharger at 15psi -- and that means it is perfectly acceptable to run with the stock intercooler, although an intercooler upgrade will give additional performance benefits. While the VJ-16 does have a bit more turbo lag than the stock VJ-14 turbocharger it is THE turbocharger for top end street-driven power. The additional tubro lag can be compensated for by simply running an electronic boost controller. For the ultimate in power look to the VJ-17 full race turbo. Only for full-race applications, as it requires an external wastegate, the VJ-17 can be had for $1,499 and has sufficient airflow to support 350HP.

Do I need to upgrade my intercooler ?
For cars driven in the 13-15 psi boost range upgrading to a very efficient intercooler and providing a cold air induction system usually yield equal benefits. The difference here is that a cold-air intake system costs a fraction of what a proper intercooler upgrade does. With a 1% gain in power for every 10 degrees F you reduce your intake temperature it doesn't take long to get another 12-15HP on a highly modified car. Of course running with both an upgraded intercooler and a cold-air intake system is the best scenario if money is not an issue.

Intercooler upgrade guidelines
There is alot of talk around from people who have replaced the stock intercooler with one from a Probe GT or MX-6GT. Although this upgrade does offer some performance improvement, the benefits are minimal. In our opinion it does not improve the situation enough to warrant the time and cost required. Now - if you already have a Probe intercooler and all the required plumbing lying around, and have some spare time on your hands, it may be a good project to tackle, as the costs are minimized. For intercooler upgrades we prefer to work with professionally built bar-and-plate race cores 3" thick or greater. The effieincy differences between one of these and a budget concious production car one are like night and day. Reich Racing is currently developing a complete intercooler upgrade kit -- one that includes all hardware and piping required to properly mount and plumb a race-level intercooler. Early indications are that a car running our ECU, Super Power-flo intake, exhaust and cat pipe at 16psi of boost will see a gain of approximately 25HP. By contrast, a Probe/MX-6 intercooler yields less than 4HP gain

_________________
*******R.I.P - The Mystery Machine BA TURBO *******


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