Author Topic: Basic Turbo Tech  (Read 2349 times)

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Offline Thundercat

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Basic Turbo Tech
« on: May 19, 2009, 11:33:01 am »
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 Standalon e 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 Standalon e setup. Apex-i's AFC's sell for less than half the cost of the standalon e system, but, the tuing capabilit ies are extremely limited. Like stated above, there are two major things you should concerned about when tuning an engine. This is some of the informati on 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 stoichiom etric air/fuel ratio, which is the chemicall y correct ratio of air to fuel for complete combustio n to take place. The stoichiom etric 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 separatel y. There are many strategie s 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 detonatio n 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 subtracti ng 1-2 degrees timing will make very little differenc e 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 associate d with a turbochar ger system. Im not going to go crazy and define everythin g as most of you probably have a good understan ding as to what everythin g 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 additiona l segments over time.

A/R- A/R means area/radius. It is a formula to determine the size of the compresso r and its turbine-housing confirura tion. 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 experienc e 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 turbochar ger and the throttle plate that bleeds off extra boost pressure. Under certain condition s 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 compresso r 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 compresso r blades or even break the turbo shaft. A BOV will release this excess pressure. Another name for a BOV is a compresso r bypass valve.

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

Intercool er-An intercool er is a heat exchanger in the intake tract that is used to cool the air that has been heated by a turbochar ger or superchar ger. There are several types including air-to-air and water-to-air intercool ers of which each has its pros and cons.

Trim-Trim is simply the size of the compresso r wheel. There are many different variation s 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.

Volumetri c Efficienc y 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 percentag e and the higher the percentag e the better.

Wastegate-A wastegate is a devise that is used to regulate boost pressure. It is done by controlli ng the speed at which the turbochar ger 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 compresso r maps (any reputible manufactu rer will supply them). Its a lot of calculati ng but it works.

1. Calculate the airflow for the engine in naturally aspirated
form. Use this formula for standard atmospher ic pressure:
(CID x RPM x 0.5 x VE) / 1728. The airflow rates will be in CFM
VE stands for volumetri c efficienc y usually 0.8-0.9

2. Knowing the desired boost level, calculate airflow rate under
boost by multiplyi ng 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 compresso r 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 horsepowe r expectati ons
Low: 0.052 x CID x (psi boost + 14.7) = bhp
High 0.077 x CID x (psi boost + 14.7) = bhp
~CREW LEGIT~JJ AUTOWERKS
~IMPORTALLIANCE.ORG~All IN FAB~BISIMOTO~

Offline Thundercat

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Re: Basic Turbo Tech
« Reply #1 on: May 19, 2009, 11:34:39 am »
How Turbos Work??-
Turbochar gers are a type of forced induction system. They compress the air flowing into the engine. The advantage of compressi ng 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 turbochar ged engine produces more power overall than the same engine without the charging, which can significa ntly improve the power-to-weight ratio for the engine.

In order to achieve this boost, the turbochar ger uses the exhaust flow from the engine to spin a turbine, which in turn spins an air pump. The turbine in the turbochar ger 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 temperatu res in the turbine are also very high.
Here is a picture to help you with this info..... ..
~CREW LEGIT~JJ AUTOWERKS
~IMPORTALLIANCE.ORG~All IN FAB~BISIMOTO~

Offline zorjin

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Re: Basic Turbo Tech
« Reply #2 on: May 22, 2009, 02:16:11 am »
cool info.. thanks


 

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