Turbocharging Info

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18-Apr-2006, 10:01 AM

91Civic_Joe

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Turbocharging Info

Ok well alot of people always have questions about Turbocharging there vehicles.Hopfully this thread can answer some if not all of there questions.. Enjoy!!

What is Octane ??-
To explain it simply, Octane is commonly know as a measurement of how much heat a given fuel can withstand before it ignites itself. When crude oil is removed from the ground and sent to be refined it is seperated into differant hydrocarbons. The most common ones are known as methane, propane, butane, pentane, hexane, heptane and octane. Some of these are fuels used on an everyday basis by many of us. Each one of these fuels has a differant point of which they become vapor or better known as their boiling point. This is the process that is use to refine the crude oil and seperate the carbons into many of the differant fuels mentioned. As well as each one having a differant boiling point; they also have a differant temperature of which they ignite themselves. Out of the fuels listed, Octane can withstand the highest temperature before it detonates. The octane rating we see on the pumps is the percentage of Octane that is present in the fuel. Most of the remaining percentage of fuel is Heptane. This percentage became known as the "Octane rating." Heptane has an Octane rating of 0. In the early part of 1900's during WWI there was a subsutite found that would artifically increase the "octane rating" of fuel without an actual increase in the percentage of Octane present. This subsutite is known as Tetraethyl lead. Fuel with Tetraethyl lead is simply known as leaded fuel.

Why leaded or unleaded??-
As explained above Tetraethyl lead was added to fuel as a subsitute during WWI to increase the Octane rating of the fuel. Tetraethyl lead was commonly used until the mid to late 1980's. The additive was removed from the fuel because lead is toxic to animal and human life. During the Late 70's and early 80's it was common to see fuel with the Octane rating of 104 at the pumping stations. The removal of lead from fuel drastically increased the cost of fuel. This increase in cost was because more extentive refining was required to obtain a higher Octane percentage or rating without the addition of lead. It also reduced the amount of emissions from the vehicle by utilizing catylitic converters. Catylitic converters can not be used with leaded fuels. The lead will clog them in minutes during operation.

Is higher octane fuel "The good stuff" ??-
The common answer to this question is yes, many cars on the market now require a higher Octane rated fuel to operate properly. Your vehicle owner's manual will designate what Octane rated fuel is required for your perticular model. Fuels that are on the market now that have a higher octane rating and actually consist of a higher percentage of Octane, not a subsutite that increase the Octane rating. Although, because the fuels octane rating is lower does not mean that it is of lesser quality than one of a higher Octane rating. You may say define quality.
The quality that is being referred to is the cleanliness of the fuel in regards to heptane present. So, the only main differance is not the purity; one can just withstand more heat before igniting itself than the other.

Is it worth the extra money for higher Octane fuel ??-
In some cases, YES !! But in others, no it is not required. Consult your owner's manual to see what the recommended Octane rating its for your model car. Performance cars tend to require a higher octane fuel than commuter cars. Cars with high mileage should use fuel that has a higher octane even though an owners manual may say it is not required. An engine's compression ratio may increase with age. This occurs when carbon deposits build up on piston domes and combustion chamber walls. An engine's compression ratio directly reflects what octane fuel is required. If a fuel is used that has a lower Octane than is required severe engine damage may occur in a short period of time. Pinging is commonly heard when the fuels octane is to low. This is really bad. If this occurs fill up with the higher Octane fuel as soon as possible. If you have a full tank, get some Octane booster at your local autoparts store.
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Piston Deburring Tech Info-
Boost is nothing but compressed air that is forced into the engine. Boost can increase engine HP. Although, there are several drawbacks from boost. Anytime a gas is compressed heat is a by product. This also works in reverse. When a gas is decompressed it reduces temperature. Such as Nitrous oxide. When it is decompressed to bar it is approximately -130 degrees.

Obviously compressed air has a considerably higher oxygen content than non compressed air. That extra oxygen allows for increased fuel to be added to the combustion chamber resulting in higher peak cylinder pressure on the power stroke. When tuned properly higher cylinder pressure directly relates to more HP. There are two different types of compression. Static compression and effective compression. Static compression is the division of the cylinder stroke volume by the combustion chamber volume. Effective compression is measured by taking bar ([14.7lbs/square inch]which is absolute atmospheric pressure)and dividing it by the how many pounds of boost the engine is under. Lets use 10lbs in our figure. 10 / 14.7 = 0.68 Add one; 0.68 + 1 = 1.68 Then multiply by the static compression. 1.68 X 10 = 16.80. As you can see the engine's compression ratio is 68% higher than it's static at 10 lbs of boost. This is a very important fact to realize.

During the compression stroke of our engine the air and fuel mixture is compressed to 10 times it's size. Remember we learn earlier that when a gas is compressed heat is a by product. This is where the fuel's octane comes into play. Octane is a rating of how much the fuel can be compressed before it ignites itself via the heat from compression and combustion chamber temps. A fuel that is suited for a 10:1 static compression engine may not be suited for an engine that has a higher effective compression ratio. The more the mixture is compressed the more heat that is generated and in turn the higher octane fuel that is required. High cylinder temperatures have an effect on the compressed gases temperature. Cooler cylinder temps enable more compression or more boost to be had for a given octane fuel.

There are several different ways to keep cylinder temperatures lower. One is to remove all carbon deposits that are built up on the pistons and combustion chamber. Second is to remove all sharp edges in the combustion chamber and on piston tops. Third is to create a thermal heat barrier in the combustion chamber to prevent the cylinder from heating up. This can be done by ceramic coating all combustion chamber surfaces and piston tops. Sharp edges and deposits are the first to heat up. These can become so hot that they can ignite the air and fuel mixture upon introduction to the cylinder. Or they can increase gas temps during compression to beyond the fuels ignition point, then detonation or preignition occurs. Here is a picture of a JE piston the way they came from JE.

The deburring of the pistons can be done at home with some supplies from or your local hardware store. You want to pick up some 200 grit sand paper. The cloth stuff is the best to use because it is a lot more durable then the paper. Basically your goal is to smooth all the sharp edges and burrs from the piston. You want to try and not remove much material just to smooth over the edges without leaving any grooves. Then, after the rough edges are gone you want to take a piece of scotch bright and make the final finish. Smooth over all the surfaces on the pistons to ensure an even finish. Here is a picture of a deburred JE piston.

There are several different companies that coat pistons. There are also kits they sell to apply your own ceramic coating. You should try to steer clear of these for the reason of the coating not being durable. It is fairly inexpensive to have them coated.Here is a picture of the same piston after coating. This piston received the Gold coat dome finish and the PC-9 low friction coating on the skirts.

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Turbo Tuning??-
There are a couple differant ways of being able to 'tune' for boost. One is a piggy bad fuel computer like Apex-i's AFC. Or a Standalone setup like Hondata or Accel DFI. Hondata's system is excellent for it's cost. Hondata's S200 is around $495. To be able to fine tune each rpm you would need a Standalone setup. Apex-i's AFC's sell for less than half the cost of the standalone system, but, the tuing capabilities are extremely limited. Like stated above, there are two major things you should concerned about when tuning an engine. This is some of the information that I gathered from the Hondata site.

Fuel is the most important. For the tuning of the fuel, the ignition timing should be set at the factory setting (16 degrees before TODC). There is a ratio of what we call Air/Fuel mixture. This is the ratio of how many parts of air there are vs how many parts of fuel there are or as a lambda value. The lambda value is derived from the stoichiometric air/fuel ratio, which is the chemically correct ratio of air to fuel for complete combustion to take place. The stoichiometric ratio is 14.7:1 when expressed as an air/fuel ratio, or 1 when expressed as a lambda value. A richer mixture will have a lower air/fuel ratio and lower lambda value. e.g. an air/fuel ratio of 13:1 equals a lambda value of 0.88, and is a typical value for a naturally aspirated engine under full load. Boosted engines need to run a little more rich that NA ones. When tuning you should set it to run rich first then lean the mixture out till you start gaining power. Once you stop gaining power, increase the mixture a little bit to the rich side to give yourself a margin for error. Then, look at the dyno chart and adjust the mixture at the rpm where you have dips in power.

Tuning of the ignition timing is the second major thing that should be adjusted. Like mixture, at first it is best to adjust the whole of the ignition table. With VTEC engines it is a good idea to do this for each cam separately. There are many strategies when tuning ignition timing, but one which works on nearly all engines is to simply advance or retard the whole ignition table 2 degrees and perform a dyno run. The tuner should keep a close watch on the Knock sensor output to insure that detonation is not setting in when the ignition timing is advanced. If the torque curve moves upwards, keep adding ignition timing until there are no power gains. If the torque curve moves downwards, then apply the opposite change to the ignition table. When retarding the timing the tuner should keep a close watch on the Exhaust gas tempature. You should find a point where adding or subtracting 1-2 degrees timing will make very little difference to the torque curve. Once this is completed the tuner should look for dips in power again and adjust the timing at that rpm.
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Glossary of Common Terms-
Here are a few of the most common terms associated with a turbocharger system. Im not going to go crazy and define everything as most of you probably have a good understanding as to what everything already is. If you would like something added feel free to contact me and i will see that it gets put in. I will be adding additional segments over time.

A/R- A/R means area/radius. It is a formula to determine the size of the compressor and its turbine-housing confiruration. Sounds like a lot but to make it simply put, the smaller the A/R the faster your spool up time and the better your throttle response. But the down side is that the top end will suffer and choke off. If you have a large A/R you will be able to flow more air but you will experience a longer spool up time and poor response also known as turbo lag.

Blow Off Valve or BOV-A BOV is simply a valve between the turbocharger and the throttle plate that bleeds off extra boost pressure. Under certain conditions like when you shift gears or when you back out of the throttle the turbo keeps spinning yet the throttle plate is closed and the air is trapped. This will lead to the air pressure getting so great that it will actually force air backwards through the turbo causing what is known as compressor surge. This will cause a huge lag the next time you hit the gas or if you are boosting high enough it can actually bend compressor blades or even break the turbo shaft. A BOV will release this excess pressure. Another name for a BOV is a compressor bypass valve.

Compressor Surge-Compressor surge is when the air pressure in the charge pipes becomes so great that it forces air backwards through the turbo.

Intercooler-An intercooler is a heat exchanger in the intake tract that is used to cool the air that has been heated by a turbocharger or supercharger. There are several types including air-to-air and water-to-air intercoolers of which each has its pros and cons.

Trim-Trim is simply the size of the compressor wheel. There are many different variations and they are not only diameter but also height, weight, curvature, fin shape and several other factors. Just remember this, in general the larger the wheel the more more volume the turbo is capable of flowing. Whether it is on the intake side which will allow higher boost levels or on the exhaust which will create less back pressure in the exhaust system.

Volumetric Efficiency or VE-VE is the volume of the intake charge on the intake stroke versus the volume of the cylinder. This is always expressed in a percentage and the higher the percentage the better.

Wastegate-A wastegate is a devise that is used to regulate boost pressure. It is done by controlling the speed at which the turbocharger spins. The easiest way to do this is to route the exhaus tthe exhaust gases around the turbine whether it be back into the exhaust or vented to open air. Also by doing this a properly sized turbo will remain in its most effective speed range. A wastegate can be set to any boost level and will remain closed until that level of boost is reached. By doing this the turbo can use all of its available exhaust energy to reach maximum boost pressure.
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How to figure out which turbo and what to expect
Because of all the quesions as to which size turbo should I use heres a little info I found on how to get a rough idea as to which size turbo to use and how much power you can expect to get from it. All you need is a little basic info and the compressor maps (any reputible manufacturer will supply them). Its a lot of calculating but it works.

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
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How Turbos Work??-
Turbochargers are a type of forced induction system. They compress the air flowing into the engine. The advantage of compressing the air is that it lets the engine squeeze more air into a cylinder. More air means that more fuel can be added. therefore, you get more power from each explosion in each cylinder. A turbocharged engine produces more power overall than the same engine without the charging, which can significantly improve the power-to-weight ratio for the engine.

In order to achieve this boost, the turbocharger uses the exhaust flow from the engine to spin a turbine, which in turn spins an air pump. The turbine in the turbocharger spins at speeds up to 150,000 rotations per minute (RPM) -- that's about 30 times faster than most car engines can go. And since it is hooked up to the exhaust, the temperatures in the turbine are also very high.
Here is a picture to help you with this info.......