Go Back   HondaShowOff.com Forums > Getting Started > FAQ - Read First

Closed Thread
Thread Tools Display Modes
Old 06-10-2005, 09:00 PM   #1
Regular User
Join Date: Jul 2004
Posts: 1,057
4doorfamilycar is an unknown quantity at this point
Send a message via AIM to 4doorfamilycar
Default FAQ - Turbos and Almost Everything to Know About Them

Source: http://www.d-series.org/forums/showthread.php?t=14212

Yes, there already is a Turbo vs. Supercharger thread, but this FAQ goes a little more in depth on Turbo alone.

Main topics and questions are bolded to make easier to find, enjoy

What is a turbo?

Quite simply, a turbo is merely an exhaust-driven compressor. Imagine a small shaft about the size and length of a new pencil. Now rigidly attach a pinwheel to each end of the pencil. One pinwheel (called the turbine) is placed in the path of the exhaust gases which are exiting the engine. These gasses are 'caught' in the turbine, causing it to spin. This in turn spins the whole shaft, along with the pinwheel on the other end (called the compressor). The compressor is placed in the intake air's path; once it begins spinning, it actually compresses the air on its way into the engine.

Why is this beneficial? Well, normally aspirated engines have to work to draw in their intake air. In other words, as the intake valves open, the piston's downward movement creates a vacuum which 'sucks in' some air through the intake system. Ideally, the piston's movement would suck in 100% of the air that could fill the combustion chamber. In the real world this is not the case; the typical engine will draw in only about 80% of the total volume of the combustion chamber. There are many reasons for this--intake restrictions, valve timing, camshaft design, and much more.

Now imagine that the engine mentioned above has a turbocharger. When the turbo compresses the air it builds up pressure in the intake manifold. Now when the intake valves open, air is actually forced into the combustion chamber. (This is one reason why turbocharged engines are sometimes referred to as 'forced-induction' engines.) As you might imagine, this allows more air to fill the chamber.

Okay, so now we have more air entering the engine. To benefit from this, we need more fuel to match. On computerized vehicles such as these, various sensors will "see" this amount of boost pressure and increase the amount of fuel accordingly. Now that we also have more fuel entering the engine, more power is made. (When you get right down to it, the only way to make more power--on any engine--is to shove more of the proper air/fuel mixture into the engine.)

How do turbochargers and superchargers differ?

While they perform the same function, turbochargers and superchargers go about it in completely different ways. As has already been mentioned, a turbo is driven by the exhaust gasses which are already being expelled from the engine. So, in effect, turbos add 'free' power since their compression is created by what was already discarded.

Superchargers, however, are different: they are belt-driven. They feature a pulley whose belt is directly attached to the crankshaft, this allowing them to spin in direct proportion to the engine itself. The upside is a near absence of lag (see below); at least some boost is typically available the instant you crack the throttle. The primary drawback to a supercharger, however, is that they take power to make power. The overall result is more power than there would be without the supercharger; it's just that they aren't as efficient as a turbocharger from an energy standpoint. Other drawbacks include lower mid-range power than a turbo, lower thermal efficiency than a turbo, (sometimes) much harder to incorporate intercooling, etc.

My new turbo is installed, now what?

Before starting the motor, it is important to get an adequate supply of oil through the turbo. To do this, disable the ignition or injectors (different for various cars) so the car is able to crank without firing. Crank the motor over for 30-45 seconds in 10 second intervals. This will pre-oil the turbo, and prevent premature thrust bearing failure.

What's the difference between 6cm2, 7cm2, and 8cm2 turbine housings?

Contrary to what your friend told you, a 7cm2 turbine housing does not have an inlet that is 7cm across. The 6cm2, 7cm2, and 8cm2 designations given to Mitsubishi turbine housings refer to the area of the cross section of the housing, known as the nozle area. In unported form, the 6cm2 and 8cm2 turbine housings have a 54mm "step bore" inlet, and the 7cm2 housing has a 60mm step bore inlet. When porting any of these housings, the step is removed, and the turbine housing is matched to a standard 7cm gasket, which has an opening that is 60mm in diameter. When porting your turbine housing, it is a good idea to port your exhaust manifold to 60mm as well.

What's the difference between internal and external wastegates?

Internal wastegates are comprised of a flapper door which is built in the turbine housing, usually operated pneumatically by a mechanical actuator. These flapper doors are limited in size, but work well in certain applications. Usually found in smaller turbos, internal wastegates are relatively inexpensive, simple in design, and very durable. Larger turbo can be fitted with internal wastegates, but boost control can be tricky. If you are looking to run high boost (20+ psi) all the time, then an internal gate may be fine. If you are looking to run lower boost levels, you will need an external wastegate.

External wastegates are generally mounted to the exhaust manifold or to the O2 housing, and are self contained units. External wastegates have the ability to bypass large amounts of air, and can provide steady boost control at any pressure level. A common myth is that in order to run higher boost pressures, you need a larger wastegate. This is incorrect. Larger wastegates are necessary to run low boost levels on large turbos.

I just bought Turbo-X, how much boost can I run?

This is a question we cannot answer for you. The amount of boost your car can handle is dependant on the rest of your setup, as every car has different flow properties and fuel capabilites. The best advice is to start low (5-8psi) and work your way up, paying close attention to your air/fuel and EGT gauges (you DO have these, right?).

What are twin scroll or divided inlet turbine housings? What are the benefits of using a twin scroll turbo?

A "twin scroll" or "divided inlet" means that there are two separate volutes within the turbine housing. The main reason for doing this is to isolate the pulses coming from each exhaust port and maintain more of the pulse energy from each cylinder all the way down to the turbine wheel. There are no differences between the turbine wheels used in open or single inlet turbines compared to those used in twin or divided inlet turbines.

Generally speaking, a divided inlet turbine setup will respond faster and produce boost quicker than single or open design of the same nozzle area, of course this is dependent upon proper execution. The simple fact that a divided housing is used does not guarantee these results.

While it does not cause any problems or harm to run a divided inlet turbine housing on a manifold that is an "open" design, none of the benefits of the twin inlet will be seen.

Why do people say it's not good to get oil feed for the turbo off the cylinder head? Should I use a filter on my oil supply line to my turbo?

There are plenty of people who have oiled their turbo off the head and not had any problems, there are just as many if not more that have done it and had recurring turbo failure that was only vaguely described by the repair shop as "poor lubrication".

Oil pressure in the cylinder head on a stock 4G63 engine can be less than 5psi at times, while this may be enough oil for a factory 14b, T25 or even 20g it isn't enough to feed the high volume oil passages of the modified thrust setup in your FPGreen or FPRed model turbo. The Garrett severe duty 360 thrust setups also have an increased appetite for lubrication. Think twice before feeding either of these type turbos from the head.

Remember that you aren't just trying to keep some oil on the bearing, you are trying to float one piece of metal above another piece of metal on a pressurized film of oil, and at the same time keep the whole mess cool enough not to melt. A constant high volume stream of oil does just that, a measly trickle will send you back to the turbo shop.

One exception to this is the Ballistic Concepts Ball Bearing CHRA from Garrett. These turbochargers are totally different internally. Their operation is actually impeded by too much oil. It is fine to supply these turbos with oil from the head. In fact the oil line we offer comes from the head and features a .8mm orifice to restrict the oil flow to the turbo . These turbos require water cooling in the absence of the typical high volume of oil that would normally provide stable temperatures.

As far as filters go, you're damned if you do and you're damned if you don't. You shouldn't need one in your oil line. Failures occur due to dirt/grit in the oil making it into the turbocharger. Failures also occur due to plugged filters. We have seen it both ways. If you are going to use a filter, check it often. The most important thing you can do to avoid oil contamination of you turbo is to THUROUGHLY wash everything more than once before assembling your engine. Avoid sandblasting anything that goes inside or onto the engine. Specifically avoid sandblasting your valve cover. If you suspect that the machine shop that did your valve job sandblasted your head then make sure you remove the 4 plugs from each end of the head that cover the ends of the oil gallies and wash the gallies out with HOT SOAPY WATER. If you do this you will be amazed at what comes out of your beautifully machined freshly rebuilt head.

If you think all that is a bunch of crap, at least spin the engine over to prime the oil system without the turbo attached so that anything in the gallies has a chance to flush out instead of flush into your new turbo.

The shaft in my turbo feels loose. How much freeplay should I have?

While this specification does vary from one brand to another and rule of thumb is less than .030" radial freeplay and less that .002" axial freeplay.

This amount of freeplay is required to allow the bearings to "float" in a pressurized film of oil while the engine is running. The flow of oil through the clearance around the bearings is what helps the bearings stay cool. This oil film around the bearings also help dampen vibrations that occur to the rotating assembly as it moves through it range of RPM. Ball bearing turbochargers do not have this pressurized film of oil around the bearings; this is why they are somewhat more noisy than floating journal bearing turbos.

My tubo is smoking and it's brand new. The shaft has normal play in it so is one of my seals blown?

The term "blown seal" is widely used to describe a turbo that has oil coming out of it. In reality a turbocharger seal cannot become damaged until the freeplay of the shaft has increased to the point where the blades of the turbocharger have been rubbing against the housings. Blade contact usually requires more than .035" of side to side movement of the shaft. In some cases it is even possible to rub the blades and still not damage the seals.

If the turbo is new and the shaft isn't loose and bouncing off the housings, but oil is coming out of it chances are you can correct the problem without even taking the turbo back off the car.

The seals within the turbo are not meant to hold back a bearing housing that has become full of oil. They are designed to sling the oil mist and spray within the bearing housing away from the point where the shaft comes out each end. If the bearing housing becomes full of oil it will ooze out past even brand new seal rings.

The oil should freely drain out of the bearing housing as quickly as the engine supplies it. This is why the drain tube is so much larger than the supply tube. Gravity is the only force moving the oil out of the turbocharger. Any slight restriction in the oil drain tube, even a small silicone dingle berry, can slightly impede the draining of the oil and cause oil to back up into the bearing housing.

The crankcase vents are the second largest cause of oil loss from a good condition turbocharger. The seals in the turbocharger were designed with expectation that the pressure inside the compressor and turbine housing will always be greater than the pressure in the bearing housing. If this is ever not the case then oil will come out pass the seals. A restricted crankcase vent will cause this to happen. If the amount of ring blowby exceeds the ability of the crank vents to release the pressure positive pressure will build within the crankcase. This pressure within the crankcase can exceed the pressure inside the compressor and turbine housings under some operating conditions resulting in oil being driven pass the seals by the improperly biased pressure gradient across the seal rings. In severe cases it may be necessary to introduce vacuum pumps to deal with crankcase pressure, but these would be very severe high boost applications where even low percentages of blowby produce a high volume of crankcase vent flow.

What is turbo lag (and how do I avoid it)?

The majority of turbochargers feature a waste gate--a valve which allows some of the exhaust gas to be directed around the turbine. This allows the turbo's shaft to spin at a reduced speed, promoting increased turbo life (among other things). Think of it as a 'stand by' mode. Since the turbo isn't needed during relaxed driving anyway, this effect is harmless...

...until you suddenly want to accelerate. Let's say that you are loafing along, engine spinning 1500 rpm or so. You instantly floor the throttle. The exhaust gas flows through the turbo and cause it to spool (spin up to speed and create boost). However, at this engine speed there isn't very much exhaust gas coming out. Worse still, the turbo needs to really get spinning to create a lot of boost. (Some turbos will spin at 150,000 rpm and beyond!) So you, the driver, need to wait for engine revs to raise and create enough exhaust gas flow to spool the turbo. This wait time--the period between hitting the throttle at low engine speed and the creation of appreciable boost--is properly called boost response. Many people incorrectly call it lag, which is really something different. Lag actually refers to how long it takes to spool the turbo when you're already at a sufficent engine speed to create boost. For example, let's say your engine can make 12 psi at 4000 RPM. You're cruising along at a steady road speed, engine spinning 4000 RPM, and now you floor it. How long it takes to achieve your usual 12 psi is your turbo's lag time. Between the two, slow boost response usually causes the most complaints.

There are two aspects to consider when dealing with boost response: engine factors and driver factors. As far as engine factors go, there are many things which affect turbo lag... although most are directly related to the design of the turbo itself. Turbos can be designed to minimize lag but this usually comes at the expense of top-end flow. In other words, you can barter for instant boost response by giving up gobs of horsepower in the upper third of your RPM range. (Behold the catch-22 in designing one turbo for all uses.)

Driver factors are another matter. You basically need to understand how a turbo works and modify your driving style accordingly. To sum it up, don't get caught with your pants down! If you feel that there may soon be a sudden need for serious thrust, downshift until your engine speed is at least 3000 RPM. This way there will be noticable boost almost as soon as you hit WOT. If you are going up a hill at WOT around, say 1800 RPM and your speed is dropping, you'll need to downshift just like any other car in the same situation. Remember: turbos need exhaust gas in order to spin. Let them have some when they need it.

What's an intercooler and how does it help?

To answer that question, a discussion of thermodynamics is involved. Turbos, as has been mentioned, compress an engine's intake air. By laws of physics, compressing air also heats it. For an engine, heating the intake air is a bad thing. For one, it raises the combustion chamber temperature and thus increases the chance of detonation (uncontrolled combustion which damages your engine). Another bad thing is that air expands as it is heated. So in other words, it will lose some of the compression effect and the turbo must work harder to maintain the desired level of compression.

Thus enters the intercooler into the equation. An intercooler is a heat exchanger--sort of like a small radiator except that it cools the charge (your intake air) rather than the engine coolant. Now that the charge is being cooled, two benefits appear: combustion temperatures decrease (along with the detonation), and the charge becomes denser which allows even more air to be packed into the combustion chamber. Exactly how much heat is removed varies greatly; some factors include the type of intercooler used, its efficiency, and its mounting location. From what I've seen, getting your intake charge temperature within 20 degrees of ambient is excellent; consider this a practical limit for a street-driven car (meaning you might get closer but not without spending tons of money).

There are two types of intercoolers: air-to-air and air-to-water. Air-to-air means that as the charge passes through the intercooler, the intercooler itself is cooled by air flowing through its fins. Picture your car's radiator but substitute the intake air where the coolant goes and you'll have a rough idea of how it works. In an air-to-water intercooler, the intercooler is cooled by a liquid rather than air; this liquid has its own radiator placed where it can receive airflow, hoses connect this radiator to the intercooler itself, and the liquid must be circulated throughout the entire system.

Each type of intercooler has its strength and weakness. Air-to-air units tend to require longer ducting to route the air from the turbo through the intercooler then back to the engine; this extra tubing might increase lag slightly on some engines and may also present interesting packaging challenges. Air-to-water units, however, can have significantly shorter intake plumbing; the intercooler can be placed in hot under hood areas where no airflow is present since the liquid coolant circulates to its radiator. This allows for simpler installation but at an expense of reduced cooling efficiency. Note that both kinds cool better when air is flowing through the intercooler (air-to-air) or the radiator (air-to-water); both kinds can benefit from the installation of a fan for low-speed operation.

Which type is better? Depends on your goal. From where I sit it seems that air-to-water intercoolers are used either for convenience--to eliminate the possible ducting nightmare of the intake--or for drag-only vehicles where a "one shot" setup uses ice to actually drop charge air temps below ambient... for a very short while. I think it is telling that a number of street cars which featured air-to-water intercoolers from the factory--such as the GMC Cyclone and Typhoon--are almost always converted to air-to-air units when upping performance is the goal. Check out an issue of Turbo magazine; you'll see these cars with huge air-to-air units mounted below the front bumper (or else behind the grill and in front of the radiator). There's a message here somewhere....

For very detailed technical information on intercooling, I recommend you visit this Buick-oriented web page. There are math formulas and lots of technical explanations which will really open your eyes to what makes for a good intercooler.

Can I mount more than one intercooler?

Sure you can; your limits will be defined by the room you have to work with and your budget. If you try this, should you mount your intercoolers parallel or in series? The correct answer is simple: in parallel. ALWAYS. Mounting intercoolers in series doubles your pressure drop, which is very bad, while mounting in parallel cuts your pressure drop in half while also allowing for more thorough cooling. Twin intercooling will cause great results; a racer's rule of thumb states you can never have too much intercooler. Here is a web page showing how one FWD Mopar fan set up parallel intercoolers in his Daytona Turbo Z.

Can I make my air-to-air intercooler more effective?

Certainly! What can be done? For starters. maximize airflow through the intercooler. This means remove anything between the incoming air and the intercooler's fins--the A/C condenser, funky ducting, or anything else that actually impedes airflow. If your intercooler isn't directly in the path of air, relocate it so that it is. If you are unable to move it around, create some sort of shroud/airdam to redirect air through the intercooler (tin or plastic should be great for this).

Another idea for you creative types is to make a mister. Get a windshield fluid reservoir, mount it where it will stay cool, and fill it with water. Now run the output tube to the intercooler. Mount a few spray nozzles aimed at the front of the intercooler's core, then join them to the output line with tees and such. Rig up this reservoir pump to a switch or button inside the car so that you can momentarily enable it when desired. The water evaporation will help draw even more heat off the intercooler, further lowering the temperature of the intake air that flows through it. You can get really fancy here; I had a friend that rigged the on/off switch to the throttle body so that the mister would activate at WOT. You can decide how to do it, but this is a neat little trick for just a few bucks.

Tips on choosing a turbine

Turbines are actually a very simple science. The turbine powers the compressor because it is a physical restriction in the exhaust flow. The more it restricts (ie: the smaller the turbine) the faster it spins the shaft... but the more it chokes the engine and robs you of top-end horsepower. The less it restricts (ie: the larger the turbine) the slower it spins the shaft... but the less it chokes the engine and the more top-end horsepower you can make. That's the key to understanding a turbine.


Select the point where the turbine housing begins and measure the cross-sectional area A at that one point. Now measure the distance between the center of this area and the center of the turbine wheel--that's the radius R. Do some division and you come up with a measurement. Now move to a different point in the turbine housing and do it again--the calculated ratio remains constant because the housing constantly gets smaller in diameter the closer it gets to the turbine wheel. When upgrading from the .48 to the .63 A/R, it's the area that changes; the radius is essentially identical. This is precisely why the .63 housing flows more air--the passage is larger!

Now you've decided your turbine's A/R ratio. Next, choose your exact turbine wheel. Turbine wheels are typically referred to in stages: StageI, StageII, StageIII, etc. One very important fact is that these stages are not universal! A Turbonetics StageII wheel is far different from a Garrett StageII wheel, for example. Make sure you know what you're getting when you ask for it.

What's the big deal about stages? This is how turbo manufacturers refer to the differences from one wheel to another. What changes, exactly? The shape, curvature, pitch and "overlap" of the wheel's blades, primarily. For a great example, look at the picture below. See how the stock wheel's blades "fold over" one another, preventing you from seeing through them? By contrast, check out all the open area between the blades of the aftermarket wheel

Factory Garrett turbine wheel verses aftermarket Garrett StageII turbine wheel:

All those open areas on the aftermarket wheel result in far less turbine backpressure, which paves the way for lots more top-end horsepower... but remember: this aggressive turbine will spin more slowly than the stock one. The slower shaft speed means the compressor spins more slowly, also. When the compressor speed slows down, your boost output falls off as well. This is why large turbines need large compressors to match!

Tips on selecting a compressor

Now that you've selected a turbine, it's time to choose a compressor to match it. You will have a variety of options. However, it won't be a case where only one exact wheel will work--instead, it's a matter of one (or two) wheels which will work best. This is where you'll need to do some math, come to grips with a few technical terms, and so on... but it still isn't outrageously difficult to do, so don't sweat it.

Speaking of technical terms, let's get right to a few of them. To understand why and how one compressor wheel flows differently than another, you need to understand the anatomy of the wheel itself. Let's take a look at the following picture:

Compressor wheel terminology:

Two key parts of a compressor are the inducer and the exducer. The inducer (sometimes called the minor diameter) is the part of the wheel that first takes a "bite" of ambient air. The exducer (sometimes called the major diameter) is the part of the wheel that "shoots" the air--now compressed--out of the turbo. Just remember that the inducer is where the air comes in and the exducer is where the air exits. Got it? Good.

You need to understand those two terms in order to grasp the concept of trim, a bizarre bit of tech-speak which is often thrown about. Trim is simply a term to describe the size of a specific compressor within a family of wheels. It can be expressed in abstract ways (such as when Turbonetics says they have P-trims, Q-trims, etc) or you can use the actual numeric measurement (50 trim, 57 trim, etc). Here's how you calculate the measurement:

Trim = (minor diameter / major diameter) ^2 * 100

So now we have a way to perform some math and get a number. What does it all mean? Generally speaking, the larger the trim the more flow the wheel will have. Nevertheless, one should not rely solely on a trim measurement when selecting a compressor wheel! Find out specific wheel measurements (inducer and exducer), understand how subtle differences will affect airflow and response, and then choose a wheel accordingly.

Speaking of subtle differences, let's take a look at them. First, the inducers:

Compressors with different inducers and identical exducers


What happens when you upgrade to a larger inducer while retaining the same exducer? The most notable change is more airflow capability; since the turbo is taking a bigger "bite" of air in every revolution, it can obviously "spit out" more air as well. Gee, more airflow sounds great... so why not go to the biggest inducer you can find? Because that creates two main problems, one much more important than the other. The smaller problem--really it's just a nuisance--is the turbo will now have a little more lag during spool up (because the bigger wheel weighs more, plus it has to do more work with each revolution, etc). While this extra lag might not be noticed on a dyno--all the bystanders will be oohing and ahhing at the huge top-end horsepower such a turbo would produce--it would make for dissatisfaction in your day-to-day drive and could even cause you to lose a drag race to a car with less peak horsepower but more area "under the curve" due to his turbo that spools sooner. The real trouble with a large inducer increase but no exducer increase, though, is it makes the turbo much more likely to surge. Surge is the situation when the compressor "spits out" more air than the engine can swallow, which causes a backup of air at the intake and it actually creates reverse-flowing pressure waves that can be very damaging to the turbo. You want to avoid surge at all costs.

Okay, so maybe we won't go hog nuts wild with the inducer. How 'bout the exducer? Let's take a look:

Compressors with identical inducers and different exducers


When you upsize the exducer without modifying the inducer, the exact opposite effect happens: your spool up time is reduced. Why does this happen? Remember that a compressor "spits out" the air in a radial fashion. The larger exducer gives a higher wheel edge speed for a given shaft speed, and that higher edge speed means the compressed air exits at a higher speed than before... and thus it builds boost faster. Another effect of this upgrade is an increase of the compressor's pressure ratio capability without a significant increase in its maximum flow rate; we'll discuss these more later on.

So now let's tie it all together. If you want more power with similar response, look for an upgrade of both diameters. The larger inducer will net you more airflow and thus greater power capability, while the larger exducer keeps boost response within reason and lessens the chance of surge.

Blow Off Valves...

Pressure release valve or more commonly known as a "Blow Off Valve", releases turbo pressure when the throttle plate is closed. The turbo is still spinning and still creating pressure. The forced air will hit the throttle plate and return where it came from. When a BOV reads vacuum from the manifold, it either opens a valve, or softens the valve. This lets the pressure escape from its opening. In order to work correctly the air must go back into the intake before your turbo because the Air Flow Meter has accounted for it. If not you will have a temporary rich condition which will upset your idle slightly. Proper tuning can get around this hassle. Most choose to vent to the air, as they love the sweet sound the air makes when it runs to the atmosphere. If the pressure release valve (as some call it) contains a horn or small holes/vents it will cause the air to make a louder/higher pitched sound depending on what is used.

Q: What is the difference between a blow off valve and a bypass valve?

A: A blow off valve will release pressure to the air, while the bypass valve will releasethe pressure into the intake system between the turbo and AFM.

Q: I installed a blow off valve, it sounds really cool but my car stalls when I let off. Why?

A: First of all, the reason this is happening is because the Air Flow Meter on our cars measuresthe air coming in through the flapper door. It senses this air and adjusts the fuel mixtureaccordingly. When you let big rush of air out of the intake system, you are letting out a bunch of air that was just measured. The fueling will still dump the fuel associated withthat air and cause an over rich condition. This will cause your car to stall momentarily orin some cases actually turn off. Once the BOV has closed and the intake system will returnto its normal state and work again.

To fix this, you need to adjust your BOV. Most BOVs have a screw or nut to adjust the tension. You can turn the screw/nut to the right and increase the tension. Do this several times with a test drive in between. If your BOV stops letting out the pressure, you haveadjusted it too tight. You will then need to start adjusting soft again. You must keep playing with this adjustment until you get it just right. A good adjustment will allow the BOV to release pressure after slight boost, and not stall afterwards. It is not necessary forthe BOV to release pressure when you rev the car.

Q: I have heard of a bypass valves being vented to air, is this possible?

A: Yes, but not right away. If you vent the bypass valve to air, your car will stumble andmost likely turn off between shifts. The reason for this is that once all the pressure isreleased the bypass valve will still be open and create a huge air leak which the AFM does not like. If you put a one way check valve on the end of the output, this will only allow the air to go out, but not in. Be sure to seal the other side of the intake where the air would normally be vented. This makes for some interesting sound effects!

Q: How can I make my blow off valve LOUDER?

A: There are a few possibilities. The first thing to remember is that there is more boost located in the piping between the turbo and intercooler, yet most blow off valves are placed near the throttle. Now, you want it by the throttle for response, but you can place it closer to the turbo for a louder sound output. Another thing to consider is to amplify the sound. You will notice that blow off valves with basic air holes are not as loud as blow off valves with horns (blitz) or air splitters (HKS). If you have a Greddy type S, the most common BOV out there, you can find something similar in style to the horn on a blitz BOV and that will make the sound output far greater. Finally, if you (or the people on the street) want to hear your bov, then you need to place it in a location that would let the sound travel out. In most cars the sound is muffled by the hood lining. Placing them out side of the engine bay on intercooler piping or similar methods will make your BOV loud and scary!

Q: Where do I get the vac/boost feed for my BOV?

A: While using the small nipples on the left/back side of the intake manifold may work, I suggest that you use the larger A/C idle adjuster hose. This will increase the response and thus the sound of your BOV. In addition to this, this hose is much closer to your BOV location.

This next question doesnít pertain to us but here you go anyways.

Q: Can I use my new BOV in conjunction with my stock type BOV

A: Yes you can but it requires some fancy fabrication. This would be the ideal setup. The stock bypass valve could handle low boost / flow situations. Which means you can tighten the main blow off valve so that it only opens under high boost. This way you have created a "double valve" system. This is not as necessary these days since twin valve designs exist.

Fuel Management

What is Stoichiometry?

Before we start upgrading a fuel-management system, it is very important to understand the dynamics of why an engine makes power. Simplified to a level that even a ricer-boy can understand, an engine requires three things to run: air, a certain percentage of fuel, and spark. An engine is most efficient when it burns every molecule of air and fuel that enters the cylinders. "Stoichiometry" is a chemical term that means the most complete combustion will take place. For gasoline, stoichiometry is 14.7 parts of air to one part of fuel by weight. Keep in mind this is only for gasoline. There are many cases where an engine will not have a 14.7:1 ratio. Start-up and warm-up are prime examples, as more fuel is needed in cold temperatures. Even when warm, an engine will only use a stoichiometric ratio in cruise or light-throttle conditions. At full throttle or for maximum power an engine will use a richer ratio. A turbo engine under boost will also use a richer mixture. A 14.7 mixture would cause a turbo motor to detonate.

TDC +/- Why is this important?

OK, so we have air and fuel in the combustion chamber. Now what? It's time to light it off. The idea here is that expanding gasses and the pressure of the burning fuel and air will push the pistons down in the cylinder, turn the crank-shaft, and transmit power to the wheels. But when, during the combustion cycle, should the pressure occur? At some point in the history of the internal combustion engine, someone figured out that the best time for maximum pressure to occur is between 12 and 14 degrees of crankshaft rotation after top dead center (TDC). If something isn't set up right and maximum pressure occurs when the piston is at TDC, the rod journal of the crankshaft will be aligned with the centerline of the crank. The result is energy directed at the main bearings, rod bearings, the block, and the cylinder head instead of making the crank rotate. This means the engine will be trying to push its crank out of the bottom or lifting the head off the block. If maximum pressure occurs beyond 12-14 degrees after top dead center (ATDC), the piston will be too far away, the pressure will be lost, and the engine will not be efficient.

What Is EFI?

An engineís fuel injection system must manage three things: how much air an engine has, how much fuel is needed to mix with the air (dependent on conditions), and what the proper timing for the ignition of the mixture will be. All the basics of power that dictate how well an engine performs are controlled by a modern carís EFI system. For example, letís say your car has a turbocharged engine and at 4,000 rpm with full boost it will require 18-20 degrees of timing. The extra amount of air and fuel provided by the turbo result in a faster burn of the mixture. But with no boost and light throttle at the same rpm, 40 degrees of timing would be needed for the engine to operate properly. Thatís quite a bit of timing range to cover and itís up to the carís EFI to figure it all out. Thatís why todayís cars are so efficient. Old vacuum-advance distributors simply donít have that type of range.

MAS and MAP?

We've discussed timing a little, so now we'll blab about air. The computer must know how much air is entering an engine so it can tell the injectors how much fuel is needed. There are a few different ways for an engine to measure the amount of incoming air.

Mass-flow fuel-injection systems use a mass air sensor (MAS) to measure the mass of the air entering the engine. Most MAS devices measure the amount of air by directing air past a heated wire that is part of an electronic circuit. Air flowing across the wire draws away some of its heat and an increase in electrical current is required for it to maintain its fixed temperature. The current necessary to heat the wire is proportional to the mass of air flowing across the wire. Most mass-flow fuel-injection systems measure the air directly, so there is no need for the engine's computer to correct for air density. Once the computer knows the amount of air entering the engine, it looks at the other sensors to determine the engine's current state of operation (idle, acceleration, cruise, and deceleration). It then refers to an electronic table or map to find the appropriate air/fuel ratio and selects the correct fuel-injector pulse width. A couple of drawbacks to a mass flow system include its price and overall design, which can restrict airflow in high-horsepower engines.

The other popular method of determining airflow is a speed density system. Unlike mass flow systems, there isn't an airflow meter that can cause airflow restriction. Speed density fuel injection systems use the speed of the engine, a measurement of manifold vacuum, and the density of the air to calculate engine air flow. This is accomplished by using a manifold absolute pressure (MAP) sensor and a pre-determined table of how efficient an engine is at flowing air in all conditions. The inherent problem with the table is that it's created at the factory and is based on a new, stock engine. The table of volumetric efficiency does not take into account wear-and-tear of an engine or if an intake or exhaust manifold was changed. To compensate for this, a speed density system uses an oxygen sensor to measure the air/fuel ratio. If the sensor is reading any errors, then the computer will correct fuel delivery of the injectors.

An injector is the engine component that allows fuel to be applied into the combustion chamber. Most import cars have one fuel injector for each cylinder. An injector works by having an internal plunger that is activated by the application of voltage. When the plunger is activated, an opening is created, allowing pressurized fuel to flow past it. An injector's primary concern is fuel delivery in all types of conditions. Fuel flow is controlled by varying the pulse width or duty cycle of the injector. Pulse width is the time in milliseconds that the injector is open, while duty cycle is the injector's overall percentage of open time.

That's a basic overview of the components in a fuel-injection system. It's important to have a background on how it works, but it's also pretty boring. What can be done with fuel injection to give your car more power is much more interesting.

Let us preface this by saying that the fuel-injection systems on modern cars are very efficient. Honda, Mazda, Mitsubishi, and everybody else have spent a lot of money and time perfecting their fuel delivery systems. A stock car and a stock EFI system work very well together. There's no real reason to modify the combo. But when you start adding aftermarket parts, things change. A stock computer should be able to handle the first steps to increased engine performance like an air intake or header. But what about a turbo or nitrous? Did the engineers who created the EFI system on a Civic foresee an owner bolting on such a thing? Don't think so. At this point an aftermarket EFI system must seriously be considered.


An aftermarket chip works by optimizing the timing and air/fuel ratio of an engine. Some car models will benefit more from a chip because they have more conservative EFI programming. German cars like VWs and BMWs are stereotypically conservative and will respond better to a chip. But if a car already has an optimized EFI setup, it will be difficult for a chip manufacturer to improve the stock EFI programming. Chips are also somewhat limited since they are only as good as the car they were programmed on. Every engine is different. If you change the setup of your car, such as adding camshafts, then the chip will no longer be calibrated properly.

Chipping your Stock Honda ECU?

This reliable way of controlling your engine can be tedious at times, yet very effective. This cheep yet effective system allows you to use your stock OBD-0 and OBD-1 ECU converted to your own needs. As you may or may not already know, your stock ECU already controls the injectors, timing, and MAP/MAS to a certain extent. Chipping your ECU allows you to change the stock settings to meet the requirements of your aftermarket components. For example; if you add a turbo (forced induction) you would need to change a few items that go with just that ďbolt onĒ! As stated above more air = more fuel, which in turn means bigger injectors. With programs like Hondata, Urberdata or Chrome you can control things like bigger injectors and timing with ease.

What are Hondata, Urberdata, and Chrome?

In short this is the software that allows you to modify your stock settings, then you to burn the program to the chip so your stock ECU can read the modifications. Then the chips go into the stock computer to make it not so stock anymore. There are many programs available, and some not so available. Hondata is one that is sold and could be quit costly with all the components. Urberdata and Chrome are free programs that are widely distributed over the internet. Yes free, even though you donít need to pay for the program you do need to pay for the burning equipment and chips.

Here is the tedious part. If you burn a chip and find the settings were not effective enough you will have to make the changes on a computer in the desired program, burn the chip and then insert it to your Honda ECU. This is where a EFI had its advantages over chipping, a few key strokes and you are done.


An aftermarket air intake or header will require the computer to add more fuel. Stock injectors can add more fuel but only up to a certain point. Increasing fuel pressure is an option, but increasing the fuel pressure changes the calibration of the injector. An EFI system bases its calculations on the known calibration of the injector. If the injector calibration is changed, the computer wonít know this and will create a fuel curve most likely detrimental to performance. The only way around this is modifying the stock computer or adding larger injectors.

Choosing the correct-size injector is always difficult. A balance must be struck between having enough fuel for full-throttle acceleration runs and being able to cut fuel output for part-throttle puttering around town. More fuel is not always better. If there is too much fuel, the engine will idle poorly or possibly even refuse to start. This is because many larger injectors will not operate with an adequately short duty cycle to lean the air/fuel mixture enough at idle.

Lucas injectors are a popular aftermarket choice for upgrading injectors. Instead of having a pintle-type design that factory injectors have, Lucas injectors have a plate-type design. The plate design allows the injector to operate with a much shorter duty cycle while still being able to provide enough fuel for maximum power. Lucas injectors also work much better with turbocharged engines because they are more resistant to the heat that a turbo creates.

Even if your engine is stock, increased performance can come from balancing and calibrating the injectors. Injectors can be defective right from the factory or become clogged after a few years of use. A clogged or improperly adjusted injector will create an uneven distribution of fuel mixture between the cylinders. If one cylinder is lean, the computer will retard the timing for the entire engine, meaning the engine will lose a lot more power than it should.

Aftermarket EFIs?

Stock computers do have limitations. The engineers of a Honda Civicís computer probably never thought that a turbo would be bolted on. Consequently, the computer doesnít recognize the changes that a turbo creates and problems will arise if the engine is boosted too much.

This is when an aftermarket EFI system should be used. Aftermarket systems allow the complete customization of an engine's timing, air measuring, and fuel delivery. For example, consider you have added a 90hp nitrous system. As we said earlier, maximum cylinder pressure should occur at 10-14 degrees after top dead center. With nitrous, more fuel and oxygen will be added and cause the flame front to travel faster, meaning the timing must be retarded, but only when the nitrous is flowing. Driving around town without nitrous and with retarded timing will translate into a pig of a car. Now consider the same car but with ACCEL's DFI system installed. The DFI system can be setup to progressively retard the timing as nitrous and fuel are applied.

Some of the more popular aftermarket systems are ACCEL's DFI system, Electromotive's TEC system, or a Motec system. With any of these systems, changing the air/fuel ratio and timing can be done with just a few computer keystrokes.

So why doesn't everybody need an aftermarket system? Because they are customizable, aftermarket EFI systems are not emissions-legal. They also require an extreme amount of knowledge to install and program. That's right, program. It's not like an air filter that you take out of its box, bolt on, and you're good to go. They must be told how to operate the engine, meaning an intimate understanding of how an engine works is required. A laptop computer and special software are needed for operation. Of course, they are quite expensive, too. So, do you think your ride is a candidate for an aftermarket EFI system? If you want more information, call the companies or check out books like Car Tech's High Performance Honda Handbook.

piggy back / piggybacking

First the definition of piggyback in computer terminology...

"The gaining of unauthorized access to a system via another user's legitimate connection." (AFCERT Computer Glossary)

Now how it works...

You will have to have a secondary computer of some sort to feed the primary computer with data. For example Apexi SFAC, Turbolink, greddy blue box, Greddy E-Manage are just a few to start. These computers will wire into your existing wire harness going from various sensors to your Honda ECU. We all understand that most of these wires are running off of electronic signals from various sensors inside of your engine bay. These different signals (from the sensor and computer) are interrupted by the ďpiggybackĒ computer and given a new signal to fool the stock Honda computer and sensor into thinking something else (bear with me here)! Now the stock Honda computer and sensors react as if the piggy back wants it to.

Letís get specificÖ

We will take your VTEC for example. Your VTEC sends an electronic signal to your stock Honda computer; we will call this signal 5 to make things easy. Keep in mind I donít know the exact #s that the signal uses, to find these exact #s use a multimeter. So, back to the 5; we will call this signal 5 at idle when VTEC is not engaged. Normally when you accelerate past a certain RPM your signal will change lets say 10. This 10 means VTEC is engaging at 6,000 RPMS. In order to change your VTEC from 6,000 RPMS to 4,500 RPMS your piggy back computer will do a few things.

First at 4,500 RPMS it will interrupt the stock signal going from the computer to the VTEC sensor and tell it to engage using the new signal 10.

Second it will tell the computer that everything is okay by giving it the 5 signal so you donít throw any engine codes.

Simple right? Well not reallyÖ

Where things get hairy is when you involve Fuel and Ignition multiplied by RPMS and Boost. This is why people say stay away from piggy back computers with lots of boost. Piggy back computers work well; well enough for changing your VTEC or Rev limiter. But when you try and change fuel maps and ignition maps things get a little crazy. Some times the piggy back canít keep up with all the signals itís taking in and processing and with a lot of boost and at high RPMS it could be catastrophic (trust me I know 1st hand, 18psi and 2 cracked pistons later).

Alternatives to piggy back computers?

There is ECU chippingÖ read about it here and thank Makku for making this up for us.

Then there is ECU replacement, AKA Standalone systems. Very complicated and super $$$, but if you have the money itís a great tool.


Piggyback computers are cheap (relatively speaking) for simple applications (VTEC or REV limiter) and a good alternative to a FMU or nothing at all. But when you spend a lot of money on a motor and plan on running a lot of boost (over 12 PSI) consider an alternative or take your chances (like I did, and lost)!
93 Ford Escort GT (Daily Driver)
Soon to come . . . 92-95 EG8
4doorfamilycar is offline  
Closed Thread


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump

All times are GMT -6. The time now is 01:18 AM.

Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
Copyright © 2003 - 2008, HondaShowOff.com