A80Girl

THIS WRITE UP IS IN THE PROCESS. I AM ADDING TO THIS DAILY.

Basically, this write up includes definitions, proper selection, purpose descriptions, and configuration tips/methods.

Generally, a lot of people I come across don’t pay as much attention to the details of turbos, wastegates, blow off valves, intercoolers, and piping as they should. So, I thought I would enlighten those who wish to learn and get full comprehension of everything turbos and to dismiss common misconcenptions/mistakes.

DEFINITIONS:

Turbine (Turbo) – A compressor driven by flowing exhaust gases used by internal combustion engines to increase the power output; Temporarily raises compression in which more air + more fuel burned = more power.

Compressor – The front side of the turbo through which intake air passes; aka “cold side”
Turbine – The rear section of the turbo through which exhaust air passes; aka “hot side”
Cartridge – Both wheels and shaft assembly (all but the housings).

Wastegate – A boost pressure actuated valve that allows enough exhaust gas into the turbine to achieve desired boost; It routes the remainder of the exhaust gas around the turbine and out the exhaust.

Boost – Pressure above atmospheric (14.68 which is rounded to 14.7), measured in the intake manifold; Generally measured in pounds per square inch (psi).

Boost Threshold – Lowest RPM in which boost from the turbo will increase power over the engine’s atmospheric equivalent (naturally aspirated compression); In other words, the lowest RPM at which noticeable boost (1-2 psi) is achieved.

Bypass Valve (Blow Off Valve) – Relieves pressure through a bleed of flow around the turbo when the engine is not under boost.

Compressor Surge – Occurs when the throttle is slammed shut and air is caught between a pumping turbo and the throttle plate. The air is pumped back into the spinning turbo, and blasts back out through the compressor. This continues until the compressor loses speed (which causes the fluttering air sound like the HKS SSQV bov).

Compressor Efficiency – The ratio of what really happens to what should happen. In the case of the compressor: measurement of the temperature gain caused by compressing air exceeds what thermodynamics says it should be. Compressor efficiency converts calculated temperature gains to real temperature gains.

Example: Raising the boost on the stock twins past efficiency raises the inlet temperature too high, over-spinning the turbos, and therefore not compressing the air efficiently to properly raise the compression in the combustion chambers. The hot air cannot cool down enough, which can cause detonation. Over spinning the turbos can also lead to shattering.

Intercooler – A heat exchanger placed between the turbo and engine to remove heat from air exiting the turbo when operating under boost.

Intercooler Efficiency – Measured by how much heat it removes relative to the heat added by the compressor.

Lag – The delay between a change in throttle and the production of noticeable boost when engine rpm is in a range in which boost can be achieved.

Thermal Load – Heat added to the system by the turbocharger; Comes from heat produced in the air that is compressed by the turbo and the mixture of heat increase due to reversion.

Reversion – Occurs when some of the burned exhaust gases are pushed back into the combustion chamber and intake system during valve overlap; Caused by exhaust manifold pressure exceeding intake pressure or by shock waves in the exhaust ports and manifold(s).

Air/Fuel Ratio (AFR) – The ratio of the weight of air to the weight of fuel in a combustible mixture.

Ambient – Refers to the surrounding atmospheric pressure and temperature.


THE BASICS:

Power Output:

So the age old debate of which method of forced induction is better: the turbo or supercharger, has been debunked for a long time. However, the common misconception that a turbocharger does not rob power from the engine still stands. This is far from true. The turbo is driven by heat and air through exhaust flow gases. When air is forced through the turbine section of a turbo, reduced flow areas built in to the system create back pressure. This creates a small loss in power. The larger the turbo, the less back pressure will occur, therefore less power loss.

Simply explained, any type of forced induction is driven by an air pump that always heats air it compresses. This is a thermodynamic law. Different kinds of air pumps heat different air amounts for the same flow rate and pressure ratios. These differences are in direct relation to the different efficiencies of various types of pumps, which is directly related to the size.

Generally a supercharger’s efficiency is around 50%, whereas a turbo runs efficiencies in the mid 70’s. The higher the efficiency, the less heating effect on the air. When you raise the boost on very small turbos past their threshold, the efficiency decreases and power actually decreases because there is increased heat, which lowers the density of the air, thus causing the engine to consume less air at the higher temperature, even if the pressures are the same. Meaning, at 20psi on a CT12, it will equal the intake air temperature density of 14psi (rough estimate). Heat in the intake charge is the enemy of performance. Consequently, the increased heat promotes detonation. Engines cant withstand the thermal and pressure shocks of detonation for more than very short periods being that the inertial load of detonation is thousands of times more powerful than combustion through a controlled flame-front.



Drivability:

It is often perceived that real power and nice drivability are not compatible. This is frequently true with NA engines but generally not with turbo engines.

So exactly defines drivability? Essentially: Get in, turn on, drive off smoothly. However, in more technical terms: A conservative cam profile, small intake ports, fuel system flexibility (as that with a deadhead setup), and calibration (the tune). Generally, a reliably, properly set up turbo car will have just that. A low profile cam that has short duration to minimize valve overlap, small intake ports to increase velocity and promote good cylinder filling at low speeds, as well as a very well calibrated electronic fuel injection system. So, its obvious that turbo cars are very economical when driven sanely. But, the turbo is there when you want to have a little fun too!


Boost Threshold:

This is a subject that really gets me going. Many people tend to judge the merit of a turbo system solely on low boost threshold. This is a serious mistake. Yes, boost at low rpms is obviously beneficiary, however that boost at low speeds achieved by small turbos is a potential problem, due to higher exhaust back pressure (and surmounting heat if you overboost!). A well designed system that has had great attention paid to all its parameters will display good low speed boost as one of its features, not its only perk!


Lag:

Rarely is there ever a conversation held about turbos without the mention of lag. However, it is equally rare that those holding the conversation are truly referring to lag, and are actually talking about boost threshold. In daily use of a turbo, sure, lag will essentially mean how long you have to wait to achieve boost after you nail the throttle. Yes, indefinitely it is a bad thing, however, lag has nothing to do with throttle response. In fact, consider this: if the car was NA, there would be “lag” from when you apply your foot to the throttle until redline!

Simply put, if you have no lag, you have no turbo. Enjoy the torque increase versus no torque increase, even if it does take a second or so. Its something to look forward to, right?

THE BASIC QUESTIONS

What kind of a power increase can you expect from a turbo?

On pump gas and a stock engine, 7 – 12 psi is a practical upper limit. Intercooling permits this when properly applied. Obviously not all turbo kits will give you the same gains on a given boost pressure due to the wide variety of engineering efforts, compilations, and/or quality of systems. Another large factor is the amount of cylinders the engine has and its compression ratio. You want to run lower boost on higher compression engines to ensure the safety of the motor by not applying too much inertial load without proper preparation. However, this mainly applies to motors with many cylinders, such as v8’s. Calculating actual horsepower gains is a challenging task without doing it mathematically. If you are unfamiliar with your motor, it is a bit difficult to predict power gains. But rest assure it will be enough.

Engines modified internally can permit frequent boost pressures of 15-20psi safely. However, this is all variable again. The 2JZ-GTE being a prime example of variance in comparison to a K20; Many different factors to consider.

__________________

My Myspace Page

A80Girl

Does the rated horsepower at a certain amount of boost of a kit have any merit? And how do I select a kit?

This is the tricky part. Many companies will promote a kit that claims to make a certain amount of horsepower. This can be true if, and only if, the conditions required to achieve that power are defined and accurate.

For Example:

-What octane gas was the car using? Is the gas available commercially?
-What was the air intake temperature?
-Is this kit setup for the same boost pressure advertised?
-Are there any other factors put in the equation (such as parts) that were used on the marketing car and are not included with the kit?
-What was the fuel pressure set at?
-What electronics/engine management software was being used at the time? What sort of tune was on it?


When considering a kit, here are some things to look for:

-Does it provide a correct AFR under all operational conditions?
-Does it provide a margin of safety over detonation (such as a knock sensor)?
-What efforts are extended towards quality control?
-Is there a warranty? If so, what are the conditions? Is it reasonable?
-Are proper instructions included or offered?
-Will consulting be provided after the sale? How reliable is customer service? Are they knowledgable?
-Are you able to do it yourself or does it have to be professionally installed?

These factors and more need to be considered when looking at a kit. Most of the time the variables for the marketing car are slightly tweaked to receive higher numbers. In other words, they tend to cheat, so be careful.

I personally prefer piecing out my own kit, however that takes time, patience, skill, and perfectionism that many people do not have. Its all up to the buyer, of course.



How do I go about with the maintenance of my turbo and the engine?

If you drive like a maniac all the time, you will obviously need to be more on top of your maintenance, otherwise expect your motor and/or turbo to blow soon.

Generally, it is recommended that you change you oil every 2000 miles. DO NOT skimp out on the quality of your oil, as this can adversely affect the life of you turbo and engine. If you use a poor quality oil, you’ll most likely develop what is known as “coking” in the oil feed line, which clogs it, thus causing either pressure build up or block oil from entering/exiting the turbo and ultimately the turbo will blow. “Coke” is basically charred oil residue that clogs in the oil feed line, or even the gravity line.

Being on top of the condition of your spark plugs is very important as well. For those running higher boost, you want the gap to be lower, while if your running lower boost you want to widen the gap. The importance of gapping is directly related to boost pressure because if the gap is too wide for the psi your running, it could blow out the spark causing rich combustion, therefor major power loss. The tell-tale sign of the gap being too wide in ratio to the boost is if once a significant amount of pressure above atmospheric is achieved (psi) when the throttle is pressed, the car will hesitate and/or break up.

Make sure you check your plugs every time you change your oil and based on your findings, decide whether you need to change them.

Another way to make sure your turbo is in good shape is to check for shaft play every once in a while. DO NOT check for shaft play while the car is on or after you ran it hard. The shaft is VERY hot, even if it is the "cold" side. I have witnessed idiots first hand sticking their fingers into a hot turbo. Not smart.

Also, it is suggested to turn your boost down a couple of psi in cold whether to reduce the risk of spiking, which could ultimately cause you to lean out. The reason for this is because air is denser in cold weather.



How can I tell if my turbo(s) is blown?

The easiest ways to tell would be:

A) If the exhaust is emanating blueish white smoke.

B) If there is shaft play

C) If the turbo has seized up entirely

Methods of checking for shaft play:

Move the shaft from side to side lightly.

Move the shaft in and out lightly.

Rotate the shaft lightly.

If you experience, any, or all of these movements, then it is blown.

The most common culprit of side to side and in and out movement is thrust washer failure, which is directly related to over-boost. Most of the time this is a very easy rebuild, however this may not be the case all the time. Over-boost can also snap the shaft entirely in half, and in the most severe cases, disintegrate the wheels. So please be conscious of what boost pressure you are running.

The most common culprit for all over shaft movement is a blown seal (there are several). This could be caused by too much or not enough oil pressure in the turbo. You can also tell a blown seal if there is blueish white smoke emanating from the exhaust, which is burnt oil. Once again, this is a relatively simple fix.

Now be aware that a VERY MINIMAL bit of shaft play is normal since the cartridge needs clearance from the housings in order to spin. However, mathematically speaking, the clearance may only be a couple thousandths of an inch.



What should I do if my turbo blows? What sort of precautions should be taken?

Believe it or not alot of things can go wrong when you blow the turbo(s).

- If the boost spiked (most common during cold weather), check your boost controller to see if it is hooked up properly.

- Depending which blow off valve(s) you are using, check the diaphragm(s) for damage. There have been many instances where the blow off valve caused turbos to blow because the diaphragm(s) had been damaged, not allowing pressure to be released from the system.

- Check your oil pressure to see if it is too high.

- Check your intercooler for oil. If there is oil, empty it out immediately. Most people do not even think of that, but it is important.

- Check your wastegate to see if it is hooked up properly. Many times people do not place the lines in the right places or T the lines which causes less pressure to leak from the wastegate promoting over-boost.

- Check your gravity line. If it is too big, then oil may be draining out of the turbo too fast. If it is too small, then oil may be backing up, building pressure. Another thing to make sure is that the gravity line does not have any kinks or bends in it; It should be a straight line down to the oil pan.


SELECTING THE TURBO

__________________

My Myspace Page