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Turbo Tech....The Real Deal.
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Special Thanks:
To- SHO members; MatT3T4,Boosted3g,Turboman,Gr3Mlin,Texan,Greyzone.
All these guys know their shit. All this info is GREATLY appreciated, and I hope they don't mind me using it here... mad props to thee guys.
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Ain't that the truth....
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TURBO TECH....FAQ and more...
Turbos Explained
-by Texan
COMPRESSOR SECTION: The compressor section is identical in function to any centrifugal supercharger, the only difference is that the turbine section of the turbo drives it. One thing to know is that turbocharger compressor sections are (generally) significantly smaller than their supercharger cousins. This all has to do with efficiency and the chosen method of powering the compressor, so just know it's the reason why you see turbochargers spinning such high RPM when compared to their centrifugal supercharger cousins. It's all about necessity.
TURBINE SECTION: This section bears a strong resemblance to the compressor section for a reason; it basically functions the same but backwards. The two main parts are the turbine housing and turbine wheel, and if this is an internally wastegated turbo, the wastegate also resides here (there will be more on that later). As exhaust gasses quickly move out of the cylinder and into the exhaust manifold, they are routed into the turbine housing's scroll. If you understood the flow of air through the centrifugal compressor design discussed earlier, here it's just the opposite occurring. As the hot and rapidly moving gasses attempt to find an airflow path through the turbine housing (with the ever decreasing scroll area), they come in contact with the turbine wheel on their way to the center outlet of the housing. As they rush through this airflow path and into the exhaust downpipe, they spin the turbine wheel, imparting a portion of their kinetic energy to the turbocharger. Especially notice that with this design comes variable RPM, the turbocharger itself is not physically strapped to any rotating part of the engine. This makes many different turbo shaft speeds possible at a single engine RPM, which is where the system's basic performance characteristics and tunability are born.
CENTER SECTION (aka bearing section): The center section is definitely the most complex of the three portions. This is what connects both the compressor and turbine sections, and where all of the cooling and lubrication of the unit occurs. Inside the center section is the main shaft, which is what the compressor and turbine wheels are directly connected to. This main shaft undergoes a great deal of pressure, RPM and heat, so the center section is unsurprisingly very specifically engineered to deal with these. The most common and basic center sections use what's called thrust bearings to keep the shaft spinning, and oil flow from the engine to both lubricate and cool the unit. Two common updates to this proven design are becoming more affordable and widespread; ball bearing center sections and water cooling in addition to oil. The ball bearing center is both more durable and more efficient at transmitting power to the compressor wheel, making it better for performance and longetivity. The water cooling is more for reliability than anything else, helping to stabilize temperatures and prevent oil coking in the housing. Both are worthwhile additions to your turbo purchase if at all possible.
TURBO KIT BASICS: Although I say "basic" here, know that this is pretty much an oxymoron when dealing with turbos. There is nothing basic about a turbo system, as many different things concerning engine operation need to be addressed. The basic turbo system should come with a bunch of different things, and few systems effectively address all these unless your car was originally equipped with the system. Here they are, in no particular order (with the little things like vacuum line omitted), and notice I left out engine management from the list, because I want to deal with that separately:
1- turbo
2- exhaust manifold for turbo
3- wastegate
4- blow-off valve (aka bypass valve)
5- lines for oil supply and return
6- intercooler (optional)
TURBOCHARGER: We've already gone through the basic explanation, but one more thing bears mention here. Ever hear the T25, T3/T4, T04e turbo designations? Well, these refer to the size and basic flow potential of the turbocharger. Garret and other manufacturers created turbo families, ones in which all members prescribed to certain physical characteristics. A T3 compressor section is one that prescribes to a specific characteristic set, such as overall size and design features. Generally speaking, larger numbers and higher letters mean a larger (and sometimes newer) family of turbos, meaning a potential increase in flow ability, power production and possibly even efficiency. The T3/T4 designation is an example of a hybrid turbo; one where a T3 turbine section has been mated to a T4 compressor section. This popular hybrid attempts to combine the excellent low RPM spool characteristics of the smaller T3 class turbo with the big flow potential of a sizable T4 compressor. Really it's a "best of both worlds" attempt, which seems to be very successful on smaller displacement, high RPM engines. Now there are a few other considerations to turbo sizing, such as A/R ratio and wheel trim, but I won't go into those unless someone really needs to know everything. The point here is simply to get a basic feel for turbo function and sizing, as the experts who designed the turbo kit or upgrade likely have already made an excellent choice in turbo size for your specific application.
TURBO EXHAUST MANIFOLD: In order to mount the turbo to the engine, the first step is to route exhaust gasses through it. This is where the special manifold comes in, dumping exhaust gasses directly into the turbine housing (provisions for mounting an external wastegate should also be found here). Usually these are fairly crude looking log style cast iron manifolds, instead of the nicely shaped and finished stainless steel header piping. But there's good reason that virtually every car to come off the production lines with a turbo follows this example: it works. Turbos build up a tremendous amount of heat and pressure in the initial part of the exhaust system, and the thick cast iron manifolds are perfectly suited to reliable performance in this environment. Also, space considerations often prohibit the use of nicely tuned tubular exhaust primaries, so there's little reason to go to the expense of crafting them. The point here is this: there are possibly some finely crafted tubular manifolds available for your application if you want maximum performance and don't mind the extra money, but these are largely unnecessary for a typical street setup. Ugly cast iron manifolds are routinely found on 400-500hp cars.
WASTEGATE: In the most basic of terms, a turbo system is self-feeding. That is, as the system creates more boost, it also creates more exhaust flow. This exhaust flow is what powers the turbocharger, so if left unchecked the turbo system will quickly spiral out of control. Now it takes time and a specific amount exhaust flow to start creating boost, but once this point is reached (called boost threshold), either exhaust flow to the turbine is regulated, or the system keeps building pressure until something gives, usually a hard part in the engine. Which is where the wastegate comes in.
Controlled by vacuum signal from the manifold (or more correctly, positive pressure in the manifold), the wastegate's job is to re-route exhaust flow around the turbine wheel to control boost levels. Remember, the turbo creates boost by extracting energy from exhaust gas flow, so this is the prime location to regulate turbocharger RPM, and therefore boost levels. What a wastegate does is provide an alternate path for exhaust gasses to flow through that doesn't cause them to contact the turbine wheel. This prevents the exhaust gasses from contributing to boost production, thus regulating boost to preset levels.
There are also two main types of wastegates, internal & external. Both are there to perform the same task, the only difference is location and effectiveness. Internal wastegates are located inside the turbine housing itself, and although effective at re-routing exhaust gasses around the turbine wheel, they can impart a good bit of turbulence to the exhaust flow path. This increases exhaust system pressure and hurts performance. The external wastegate, the true performance choice, has provisions made for it's mounting before the turbo on the exhaust manifold. An entirely alternate flow path is created where exhaust gasses skip going through the turbine housing altogether, contributing much less to turbulence in the system. They also tend to be more accurate at controlling exhaust flow and turbo boost; combine these two attributes and you have a recipe for superior performance.
BLOW-OFF VALVE: this is both the insurance policy of the turbo system, and it's protector. Two things are governed by the blow-off valve; maximum boost levels and pressure spikes in the intake tract. While the first job is primarily handled by the wastegate, in the event of a big enough overboost, the blow-off valve will vent excess pressures to help maintain safe levels of boost. Basically, the blow-off valve is a springloaded poppet valve contraption that will bleed off and excess pressure that builds up in the intake system. This can occur due to either boost creep or a sudden closing of the throttle body when boosting (such as during full throttle, high RPM shifts), but either way it's the blow-off valve's job to prevent pressure spikes in the intake tract. This serves two functions: one, to prevent serious engine damaging overboosts, and two, to prevent airflow from reversing direction into the turbocharger itself. The second one is it's principle job, to keep the intake tract from building up large pressures during sudden lift throttle situations (such as shifting).
When the engine is at full boost and full song, the turbo is spinning madly to supply air to the intake system. The momentum of air and turbocharger are not easily stopped on a dime, so when the throttle body is suddenly slam shut, things tend to get interesting in the intake system. There is an immediate pressure spike between the turbo and throttle body, putting great stress on the compressor wheel which is still trying to pump air into a closed system. To keep the turbo's RPM up and the pressures in the intake tract down, the blow-off valve vents this excess pressure for maximum performance and reliability.
INTERCOOLER: This is the most important performance part you can add to a forced induction system, and is well worth its price if boost numbers rise beyond 8 psi. Compression equals heat, and blowing hot air into the engine is neither efficient or reliable. An 8 psi forced induction system can produce air inlet temps over 200 degrees farenheit, making the engine a detonation machine. The greater amount of space between the air molecules also lowers charge air density, meaning the 8 psi of air isn't as potent as it could be. The solution lies in cooling the air charge before it enters the engine, and that's precisely what the intercooler does. Two types of these are in production, air-to-air and air-to-water intercoolers. Air to air intercoolers are inexpensive and easy to maintain, but they can be very large and must be in a good airflow path to be effective. They are also rarely over 80% efficient, meaning the charge temps only get to within 80% of ambient during engine operation. Air to water systems are more compact but also more complex, their biggest advantages lie in placement freedom and efficiency. An air to water intercooler does not need a supply of fresh air and can be well over 100% efficient (when filled with a cooler than ambient liquid), but they do need an external reservoir of coolant and some means to extract heat from that coolant. Traditionally, air to air units are preferred for simplicity, reliability and effectiveness in street cars, while the superior cooling and placement possibilities of air to water systems are most at home in drag vehicles (or ones that only see occasional boosting, where heat soak isn't an issue). There are of course exceptions, and in fact the Jaguar XJR uses air to water intercoolers, but these are few and far between. At any rate, either system is universally a good thing if you plan on running even moderate levels of boost.
OIL SUPPLY: A lot of people pass this part up when explaining a turbo system, and yet it's one of the main things you will have to deal with on any turbo install. The turbo needs both a supply and return line, where the supply line is generally in the form of a sandwich adapter mounted between the oil filter and engine block. The return line is usually the pain in the ass, since the oil pan of the engine needs to be removed and fitted with provisions for this line to connect to. Some aftermarket oil pans have NPT bungs on them ready for this type of use; I highly recommend you think about buying one of these (which is always a good investment even without the turbo) if you are planning on a serious turbo buildup.
TURBO BUILD-UP
-by MatT3T4
Stage I: The Daily Driver
~~Light buildup, daily driveability/reliability, inexpensive, occasional racer, mostly street legal.
-Civic SOHC; VTEC & non-VTEC
Turbocharger
>GReddy turbo kit
>GReddy intercooler kit: small one
>GReddy Type-S blow off valve
Ignition
>MSD 6A
>MSD Blaster 3 Coil
>MSD Pro Cap
>NGK Blue Wires
Fuel
>Holley 255LPH In Tank Fuel Pump
>B&M Command Flo
Exhaust
>GReddy EVO
>Random Technology Hi-Flow Cat
Bolt-Ons
>AEM cam gear
Tuning
>A'pex V-AFC: for VTEC
>A'pex S-AFC: for non-VTEC
>GReddy 2mm Metal Head Gasket
>Missing Link Check Valve
Gauges/Electronics
>GReddy boost gauge
>GReddy air:fuel meter
>GReddy oil pressure gauge
>GReddy turbo timer
>GReddy Profec A or B boost controller
---E.T.A.---
Quarter mile times can drop to as low as low 13's depending on your setup. Good tuning, ample fuel & spark, with race gas, and about 14psi will net you 13's. Safe street driving with this setup well tuned should be around 10psi.
Stage II: The V8 Killer
~~Serious about being fast on the street, looking for at least 12 second runs. Does not care about street legality, reliability is still good, but must be cared for excellently.
-SOHC & DOHC HA Cars; VTEC & non-VTEC
Turbocharger
>Rev Hard Stage II; DRAG Gen III; F-MAX
Ignition
>MSD 6AL
>MSD Blaster 3 Coil
>MSD Pro Cap
>Aramaki or NGK
Fuel
>Holley 255LPH In Tank Fuel Pump
>AEM fuel rail w/ fuel pressure riser
>RC 370cc-440cc injectors
Exhaust
>Thermal R&D 3"
Bolt-Ons
>AEM cam gears
>ITR or Skunk2 intake manifold
>RC ported throttle body
>Web Cams; or some other sort of turbo cam
Tuning
>DFI
>InLinePro head gasket
Gauges/Electronics
>GReddy boost gauge
>GReddy air:fuel meter
>GReddy EGT gauge
>GReddy oil pressure gauge
>GReddy turbo timer
>GReddy Profec A or B boost controller
Clutch
>Clutchmasters; ACT; Clutch Specialties; etc...
---E.T.A.---
Easy low 12's, maybe even high 11's depending on your tuning, and the size of your cajones. Safe daily driving boost setting should be around 10psi with good tuning, and track spec, with race gas, can be anywhere from 15-19psi or so.
Stage III: I AM GOD!
~~You do not give a crap about laws, you have a fat wallet, and reliability is for the weak! You want to DRAG RACE. You don't care about twisties, and you don't care about cops. You want to own everyone!
-SOHC & DOHC HA Cars; VTEC & non-VTEC
Turbocharger
>Rev Hard Stage III; Custom
Ignition
>MSD 7AL
>MSD Blaster 3 Coil
>MSD Pro Cap
>Aramaki wires
Fuel
>Holley 255LPH In Tank Fuel Pump
>AEM fuel rail w/ fuel pressure riser
>RC 550cc+ injectors
Exhaust
>Thermal R&D 3"; or just downpipe
Bolt-Ons
>AEM cam gears
>sheet-metal intake manifold
>RC ported 70mm throttle body
>Web Cams; or some other sort of turbo cam
Internals
>JE Pistons
>Total Seal rings
>CROWER rods
>Bensons sleeves
>micropolished crank
>ARP rod bolts & head studs
>Bensons port/polish head
>Crower valvetrain (springs/retainers/valves)
Tuning
>Accel DFI; Haltech; Motec
Gauges/Electronics
>GReddy boost gauge
>GReddy air:fuel meter
>GReddy EGT gauge
>GReddy oil pressure gauge
>GReddy fuel pressure gauge
>GReddy turbo timer
>GReddy Profec A or B boost controller
Clutch
>Clutchmasters; ACT; Clutch Specialties; etc...
Limited Slip Differential
>Quaife; KAAZ; JDM ITR tranny
---E.T.A.---
Sheeeeeeit!
TURBO TIPS!
-by MatT3T4
~Stay cool: Turbo's need turbo timers. When you are driving around town, 30-45 seconds really is ample time for it. What it does is it keeps the motor running, which keeps pumping oil through your turbo. The longer it runs, the cooler the oil will be that is going through it. The reason you want cooler oil in it when it finally stops is that if you just shut it off, the hot oil will cake onto the surface, and in time, the oil seal will break, and you will need a turbo rebuild.
~Aftermarket Hoods: Hoods with vents are good! Especially during the summer. Our turbocharged cars run slow during hot summer days, and that's a fact. One way to partially remedy this is the use of a vented carbon fiber, or fiberglass hood. I used to have one on my car, and I did see results. I'd even pull up at a red light, and I could see the heatwaves rising up out of it, allowing my engine bay to cool down. Heat-soak sucks!
~Windshield wiper sprayer...no, INTERCOOLER SPRAYER!: Who needs windshield wiper sprayers with so many gas stations with squeegee's?! Re-route your windshield wiper sprayers down to your bumper right above and in front of your intercooler. During hot summer days, when you are sitting at a red light baking, hit the sprayer, and douse your intercooler. The evaporation aids in the heat exchange process, and helps cool your intercooler, in turn, helping to cool your intake charge slightly.
Engine Blow Diagnostic
-by MatT3T4
~blue smoke:oil burning. Possible piston ring failure, wear and tear. Could also be the valve guide seals.
~white smoke: Water/Coolant entering into the combustion chamner. This could be caused a many things such as a cracked head gasket, cracked block or head, etc...
~milky coolant: cracked head gasket, cracked block or head.
~severe knocking in motor: Spun rod bearing. Car will most likely stall out. Oil light will probably come on, and reservoir around oil cap and/or breather will be leaking oil.
TURBO MATCHING:
1. Calculate the airflow for the engine in naturally aspirated form. Use this formula for standard atmospheric pressure: (CID x RPM x 0.5 x VE) / 1728. The airflow rates will be in CFM VE stands for volumetric efficiency usually 0.8-0.9
2. Knowing the desired boost level, calculate airflow rate under boost by multiplying the pressure ratio by the airflow rate (NA-CFM). To figure out the pressure ratio take (14.7 + boost) divided by 14.7.
3. If you are runnning twin turbo divide the total cfm under boost by 2.
4. To convert CFM to lbs/min, use (CFM x 0.076= lbs/min).
5. Use compressor maps to find the turbo best suited to the airflow rate and pressure ratios you have obtained.
Heres a low and a high range for horsepower expectations:
Low: 0.052 x CID x (psi boost + 14.7) = bhp
High 0.077 x CID x (psi boost + 14.7) = bhp
All information was obtained from HKS USA
ECU CODES
Code & Meaning
1.....O2A - Oxygen sensor #1
2.....O2B - Oxygen sensor #2
3.....MAP - manifold absolute pressure sensor
4.....CKP - crank position sensor
5.....MAP - manifold absolute pressure sensor
6.....ECT - water temperature sensor
7.....TPS - throttle position sensor
8.....TDC - top dead centre sensor
9.....CYP - cylinder sensor
10.....IAT - intake air temperature sensor
12.....EGR - exhaust gas recirculation lift valve
13.....BARO - atmospheric pressure sensor
14.....IAC (EACV) - idle air control valve
15.....Ignition output signal
16.....Fuel injectors
17.....VSS - speed sensor
19.....Automatic transmission lockup control valve
20.....Electrical load detector
21.....VTEC spool solenoid valve
22.....VTEC pressure valve
23.....Knock sensor
30.....Automatic transmission A signal
31.....Automatic transmission B signal
41.....Primary oxygen sensor heater
43.....Fuel supply system
45.....Fuel system too rich or lean
48.....LAF - lean air fuel sensor
54.....CKF - crank fluctuation sensor
58.....TDC sensor #2
61.....Primary oxygen sensor
63.....Secondary oxygen sensor
65.....Secondary oxygen sensor heater
All ECU info gathered from HonDATA.com
Tuning With An EGT Gauge
-by MatT3T4
The process of carburetor tuning is greatly simplified with an EGT gauge (Exhaust gas temperature gauge). An EGT does not tell you exactly what the mixture ratio is, but it does give you a pretty fair indication of what is happening inside of the engine. If the mixture is rich, the temperatures will be low, and if the mixture is lean the temperatures will be high. There is no exact number to aim for, as exhaust gas temperature is affected by many things. A typical race engine seems pretty happy at about 1650 to 1700 degrees Fahrenheit, and turbo engines seem to run best with temperatures 150 to 200 degrees less.
After installing your gauge, make a run at full throttle in third gear, and monitor the temperatures throughout the rpm range. If for example, the gauge reads 1400 at 4000 rpm, and creeps all the way up to 1850 at 8000 rpm, the engine is running rich at low rpm, and lean at high rpm. At some point in the range, the engine will feel strongest, and the temperature at that point should be your target, give or take maybe 100 degrees. It is normally best to correct the low rpm mixture first, and then correct the high speed mixture. The first step would be to decrease the fuel jet one size, make another run, and see what happens. If at this point, the temperature throughout the low and mid range is steady, and the high rpm still reads lean, decrease the air bleed and make another run. Continue making changes, and monitoring the results. This will involve a fair amount of trial and error, but after a few runs, you will get a feel for the effects of the jet changes, and the temperature that seems most appropriate for your engine. This is much easier than it sounds, and after a while you will begin to predict the effect of jet changes
Tuning With An Oxygen Sensor
-by MatT3T4
An EGT gauge is a great tool for tuning full throttle mixture, but it is not at all helpful for tuning idle and cruise mixture. An oxygen sensor, or lambda sensor can be used to properly tune the fuel delivery system for gas mileage and driveability. An O2 sensor works by sampling the amount of oxygen present in the exhaust gasses. An oxygen sensor responds much quicker than an EGT gauge, and its output is extremely accurate at mixtures of 14.7:1 and leaner. At mixtures richer than that, the output becomes temperature dependant and loses its accuracy. While all of the O2 sensors on the market have a display that reads from about 16:1 to 12.5:1, they simply cannot be relied upon at richer mixtures. Dyno testing has shown that a difference between 11:1 and 13:1 is almost unnoticeable in the output of the sensor. While full power is achieved at a ratio of 13:1, optimum gas mileage and emissions output occur at a mixture of 14.7:1.
Now that you know how fuel changes affect the mixture, you can monitor the output of your sensor and change idle and fuel jets to achieve optimum mixture at idle and cruise. The idle circuit continues to supply fuel to the engine at cruise, or any time the throttle blades are only slightly opened. After installing the unit, simply drive the car as you would during normal driving, and monitor the output of the sensor. If the mixture is richer than 14.7:1, simply decrease the fuel supply. You can also increase your fuel mileage by making the mixture lean under light acceleration. The engine will make slightly less power during light acceleration, but gas mileage will improve (this is not a good idea with turbo charged engines because they will still enter into boost under light acceleration). Full power mixture can then be tuned with the EGT gauge. If you have both units installed in your vehicle, you can tune your fuel delivery system to work exceptionally well.
EGT Monitoring
-by MatT3T4
EGT monitoring can be a very effective tool in tuning, but “ideal” EGT can vary from engine to engine dependant upon combination. Usually, 1300 to 1500 degrees F is optimal for normally aspirated engines on gas, while gas turbos will run optimally @ 1500 to 1650. An important note: this is measured before the turbo, not after, as the turbo will reduce EGT by an average 200 degrees F.
Finding the optimal EGT signature for your engine is a trial and error (hopefully more trial than error!) procedure, and other factors such as power output, plug readings and air fuel ratio equipment should be used to corroborate the data. Once you have ascertained this ideal EGT, it should be repeatable regardless of climatic conditions: simply tune for the same previously determined optimal EGT, and your engine should perform at full available output under any ambient conditions.
A common mistake made by new users of EGT: high temps indicate lean condition. Not always true! Excessively rich conditions will result in “after burn”, where the fuel, which was unable to completely combust due to insufficient oxygen in the cylinder, lights off in the exhaust system, causing an unusually high temperature reading. If all other indicators still suggest a rich mixture, try leaning in small steps, and you will likely see the EGT go down. Just be sure that the power does not also go down from the changes. If you are on the right track, power should go up noticeably as you lean towards optimal mixture while EGT drops. As you approach and then pass the optimal mixture point, the EGT will begin to climb again. STOP! Richen by one step and you are there! Now, when climatic conditions worsen (i.e.: hotter temperature, more humidity, less air density), lean until you get that optimum EGT again. If conditions improve (colder weather, lower altitude, less humidity), richen for optimal EGT. Bear in mind: if EGT suddenly changes for no apparent reason, you may have an aggravating factor (ignition problem, fuel pressure wrong, clogged air inlet, etc.) which is unrelated to tuning. Be observant, and the indicators should guide you to the right tuning decision.
Important: Air fuel ratios, which are not optimal throughout the entire available RPM and manifold condition range, will mislead you. In other words, an optimal EGT signature at high RPM may not show an incorrect condition at lower RPM or different manifold pressure. Although perplexing, this problem is truly the difference between a happy, powerful and long-lived engine and one that is trying to destroy itself slowly but surely. It is one reason why the precision of fuel injection is usually superior to carburetion in both power production and engine life. Just watch ALL the indicators, and remember: lean is mean, and fuel is power. Instead of continuously trying to lean it for maximum HP, try to find ways to get more air to the engine, and thusly support the combustion of more fuel. There’s only so many BTU’s in a gallon of fuel, no matter how you burn it. Just try to burn more fuel!
AIR/FUEL METERS
-by MatT3T4
It is possible to monitor the output from the O2 sensor using a volt meter between the sensor and ground. Even people with non-fuel injected engines can install an O2 sensor in the tail pipe and use the readings for tuning purposes. If memory serves, most people are looking for about .82 volts under maximum acceleration. Since the O2 sensor is relatively insensitive in that part of its range, the reading is best used in conjunction with other indicators to find that perfect mix. A more elegant choice is to buy an Air/Fuel meter.
The first problem in talking about A/F meters is that there are two classes of instruments out there. Laboratory grade A/F meters are costly, and not meant for permanent installation. They are accurate in all ranges, and not bothered by changes in exhaust gas temperatures. Thus, their sensors can be temporarily placed in the tail pipe. These instruments have digital readouts, and are the ONLY reliable way to do fine tuning on an engine if you are looking for absolute information about high performance A/F ratios.
Inexpensive Air/Fuel meters express the output voltage of the car’s O2 sensor as an A/F ratio displayed with LEDs. These meters come in several shapes and sizes. The primary flaw in their usefulness is that they cannot be more accurate than the information coming from the O2 sensor. However, they are small enough to mount permanently on your dashboard, bright enough to glance at when driving assertively, and cheap enough to be a worthy addition if you start messing with your car. They respond very quickly, alerting you if your latest “improvement” causes lean running, or if something in the fuel supply system malfunctions.
What the inexpensive A/F meters won’t do is to give you a high resolution, accurate reading of a performance oriented A/F ratio. The range of most of these meters is about 16:1 on the lean side, to about 12:1 on the rich side, and most of the LEDs are unmarked. Two factors become obvious here: First, if you are looking for an A/F ratio near 12.5:1 an A/F meter of this type will be close to the end of its range (where the information coming from the O2 sensor is least sensitive). Second, if the “rich” side of your A/F meter only contains five or ten LEDs above stoichiometric, you won’t have enough resolution to see very small changes. While these limitations seem to damn inexpensive A/F meters to near uselessness, that is not the case. The information they give you, when combined with other observations and experience with the car, can be very valuable—especially if you have some manual control of your fuel delivery system via the typical add-ons (additional injectors, boost dependent fuel pressure regulators, fuel computers, etc.) associated with aftermarket turbos, or with upgrades for stock systems. The resolution on the meter is consistent with the quality of information coming to it from the O2 sensor. So, even though the absolute readings may not be reliable, seeing if the reading stays constant as revs and boost build is very valuable.
FUEL
-by MatT3T4
There are several excellent sites on the web about gasoline, so comments here will be limited to octane and its effect on knock. One of the reasons the original question (less octane equals leaner running?) was so hard to answer is that you are unlikely to find two fuels that differ only in octane—especially when you are dealing with racing gas. The notion several people had was that higher octane fuel gives off more energy. Thus, if (for example) a teaspoon of higher energy fuel explodes, it will burn more oxygen. This will result in less oxygen in the exhaust. The O2 sensor will develop more voltage and the A/F meter will give a richer reading. It certainly seems logical.
The problem is that octane is simply a measure of a fuel’s resistance to knock (more on knock later). There is no implication I could find that by changing octane alone you would also make a fuel release more or less energy. So, if everything else was left alone, and you put a bottle of octane enhancer (like 104+) into a tank of 93 octane fuel, your A/F meter would not change its reading.
In the real world, high octane racing fuels are denser and pack more energy in each “teaspoon.” A lab grade A/F meter will display the difference as a richer reading. Thus, there are at least two advantages to racing fuel. You have access to more energy at the same fuel flow, and the extra octane will allow you to run at higher boost levels. An off-the-cuff comment by someone in the know was that you need to raise the octane rating by three points to accommodate one additional psi of boost. This echoed another comment—that a 3rd gen running at 14 psi on pump gas could get as high as 18 psi on the highest octane race fuel. Don’t try this at home, kids.
Interesting Note: The “Reference Library” section of http://www.lubrizol.com states that cars need additional octane as they age due to the buildup of deposits in the combustion chamber. These deposits take up space, which effectively raises compression. This explains the knocking observed on a number of aging cars. All responded positively to
higher octane fuel
EXHAUST GAS TEMPERATURE GAUGES
-by MatT3T4
Many swear by these gauges because they get an “absolute” reading of temperature. On the positive side, EGT gauges are not subject to the non-linearities of an A/F meter. If you can repeat the same scenario, you should get comparative readings. So, for instance, if you note the EGT reading after doing a full throttle run from 3000 rpm to red line at 10 psi, then do the same thing at 12 psi, you should be able to see the difference on an EGT gauge. The same can be said for altering your fuel mix, installing a bigger intercooler, and maybe even changing your timing (retarding timing results in higher exhaust temps). Further, there are known parameters out there for exhaust temperatures. Some race engines run between 900 and 954 Celsius (1650-1750F). An ’89 fuel-injected pro SCCA car was happiest at 773 Celsius (1425F). Because of the wide range of “best” exhaust temperatures, anyone who assumes his or her engine is happy based solely on the number appearing on an EGT gauge is taking a risk.
This brings us to the “down side” of EGT gauges. The temperature reading is influenced by the location of the probe: usually on the manifold, but sometimes aft of the turbos or even further aft than that. A second problem is the response speed of the unit. A race car, running “full out” on a track, has plenty of time to develop a stable exhaust temperature. Running on the street, most of us can’t tell whether the gauge is registering the real temperature, or if it was just on its way up there when we had to let off the gas to keep from ramming the nice person in the SUV who pulled out in front of us. For street use, you have to get used to what the EGT gauge is doing, and be aware of differences when you change something on your car. A third area of concern is that the EGT gauge (like the A/F meter) will tell you when something has changed, but neither will tell you exactly what it might be.
Example: After an autocross run, the “peak-hold” feature on an EGT gauge showed it was only reading about 775 Celsius. Normally on the street it would read about 825C after spirited driving. The water temperature gauge showed that the car had heated up by almost 10 degrees (F) during the run, so it is likely that the EGT gauge did not have time to come up to temperature. In this example, if you leaned the A/F mixture based solely on what the EGT gauge was showing, you would have been taking a risk.
PRE-IGNITION AND KNOCK
-by MatT3T4
Detonation; Knock; Ping; Preigintion. You hear these terms mentioned all the time, so we might as well straighten them out. Let’s get preignition out of the way first. Nothing mysterious about it. The A/F mixture (intake charge) explodes before the spark plug fires. You would figure the intake charge would have to get pretty hot to do that, and you would be right. The pressure from a high compression engine is enough to generate that kind of heat. (In fact, diesel engines are designed to fire on the heat from compression alone.) Higher octane fuel is the antidote, so in general, a higher compression engine will need higher octane fuel. Cramming more intake charge into the combustion chamber has the same effect as raising compression, so in general, the higher your boost, the higher the octane requirement to avoid preignition. Finally, premature ignition occurs more readily if the intake charge is hot when it enters the engine. This is why larger intercoolers add a margin of safety in forced induction engines—at least until you turn up the boost.
Another cause of preignition is a hot spot in the engine. Maybe some of those carbon deposits are glowing red hot. Maybe the spark plug itself is hot enough to ignite the mixture before firing. This is almost certainly the case if you have ever experienced a car that kept trying to run after you turned the key off. The more tricky term is “knock.” Although most of us prefer to talk about “detonation,” it turns out that “knock” is the correct term as used in automotive texts. “Detonation” is actually slang, and “ping” is not a well defined term at all. That having been said, we will stick with the term “detonation” for this discussion.
Detonation differs from preignition in that it occurs AFTER the mixture starts to burn. Normal burning involves a flame front—a relatively slow, controlled explosion—which marches along in a calculated fashion. As you would expect, normal burning raises the pressure in the combustion chamber. Sometimes this is enough to get the last bit of intake charge (called the “end gas”) so excited it explodes before it is supposed to. It is a very hot explosion, on the order of ten times the heat of controlled combustion. But there is more to it than that. If you graph the amount of pressure in a combustion chamber during normal burning, it shows a relatively smooth event. The occurrence of detonation shows up as a sharp spike on the graph—a sudden shock wave if you will, with pressures on the order of several thousand psi. The duration and strength of the explosion is too fast to contribute to the rotational output of the engine. Like a slap in the face, the full impact must be absorbed within the combustion chamber itself. Damage is most likely to occur at the weakest points. Piston engines designed for high stress situations can have the piston rings further away from the crown of the piston. The shock of repeated detonation will eventually weaken anything it can, and the heat generated will take care of the rest.
Question: How would this show up on standard gauges?
This is where we get into speculation. Changes in the engine happen so quickly that any hint of knock must be accompanied by getting off the gas. Yet even this is not simple. What happens if your exhaust (or music) is too loud to hear the knock? And what happens if, say, only a very small amount of the “end gas” detonates? Would you see the results on a gauge? Could you hear it? Could it damage your engine if it was allowed to continue? How about the specter of preignition combining with detonation? Answers to most of these questions would include so many qualifying statements (“...it’s possible that maybe under certain circumstances...”) as to be of little use, but we can still deal with knock in a direct manner.
KNOCK SENSORS
-by MatT3T4
Some engines come with knock sensors integrated into the electronics. Knock sensors use a microphone—usually on the engine block or intermediate housing. The mike feeds electronics which are tuned to recognize knock from the engine. Once identified as knock, the computer intervenes by retarding the ignition timing. Why does this work? Gasoline engines are usually set to fire the spark plugs before the combustion chamber reaches its smallest size (maximum compression). On a piston engine maximum compression is when the piston is at the top of the compression cycle. In other words, the mechanical compression cycle is not complete at the time the plug fires. Thus, during combustion, the total pressure in the chamber is a combination of the remaining part of the mechanical compression cycle plus the pressure from expansion caused by the burning fuel/air mixture. If you delay the firing of the spark plug, more of the mechanical compression cycle will have passed at the time the intake charge is lit, so the overall amount of pressure (and heat) in the combustion chamber reduces. This reduction in pressure should be enough to ease the tendency for the end gasses to detonate. This is why the more you retard the spark, the more relief you get from detonation.
Those with aftermarket turbo kits can add a knock sensor. J&S makes one that intercepts the firing signal going to the leading plugs and delays it in proportion to any knock that is sensed. The unit is very sophisticated, and can identify which cylinder is associated with the detonation. It then retards the spark to that cylinder only. If more than one cylinder is involved each one is treated independently. Owners of highly modified factory turbo cars can also benefit from such a device since the range and capabilities of stock knock sensors may not be enough to fully protect an engine that is exceeding factory output.
Home Compression Test
-by MatT3T4
Think you messed something up? Think you may have lost compression in one of your cylinders? Well, there is one easy way to tell without having to drive to your mechanic to get a compression test. Do as follows:
1- Turn on ignition and start motor.
2- Let the car idle until warm, and have a steady idle.
3- Starting with cylinder 4 on the left side of the motor, pull out each spark plug wire one by one, and listen for idle drop. Replace spark plug wire before testing next.
What should happen is the following:
1- If your motor is alright, when you pull out the spark plug wire in each cylinder, the idle should drop significantly.
2- If the motor is damaged, and one or two cylinders in particular are the culprit, then when you pull out that spark plug wire from that cylinder, the idle will NOT change, but it will remain constant, and that means that you are NOT getting compression in that cyldiner, and that is the root of the problem.
If you try this, and the idle drops each time, then your bottom end is not the root of your problem. If it does not drop in any particular cylinder, then that cylinder could be cracked, scratched hard, or that piston ring could be burnt beyond belief.
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All I can say is "holy shit" and thanks ALOT....
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