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Engine turbo systems 


West Coast Fiero turbo charging systems and parts
 

Turbochargers make torque, not horsepower; horsepower is a function of how much torque the engine produces at a given RPM.  In order to increase HP without increasing torque, you will need to increase the engine RPM.  Most of the wear, tear, and abuse in an engine is going to come from increasing the RPM because of a simple law of physics:  Force increases with the square of the speed increase.  In simpler terms, as you double the speed of an object, its force increases fourfold. These are the forces that tend to tear an engine apart.

A much safer and cheaper way to increase the engine’s power output and staying in the same RPM range is done by increasing torque.  With a properly sized turbo you could double the torque of the motor at a given RPM while only increasing the peak force on the engine 20% or so.  It sounds far fetched, but here's how it works:

 
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Keep in mind that the pressure in your combustion chamber is a combination of how much pressure your piston created when it compressed the fuel mix and the pressure from the burning mix. This fuel mix will burn in your combustion chamber at a certain speed depending on mixture, pressure, and other factors, but it does not burn instantly.   In a combustion engine the peak pressure is reached near the top of the stroke when a small portion of the fuel mix has burned.  After that point the piston is accelerating downward and the cylinder pressure drops off rapidly while the fuel is still burning.

In a turbo engine under boost, you may have twice as much fuel and air mix in the combustion chamber.  Since the fuel does not all burn at the same time, this additional pressure does not add much to the total cylinder pressure that would have existed in a normally aspirated engine.  As the piston is accelerating downward there is more burning fuel and air in the combustion chamber which pushes harder on the piston. This is where the real power increase in a turbo engine takes place.  At about 90 degrees crank angle, the turbo engine's fuel mix can push 3 or 4 times harder  on the piston than a normally aspirated engine would push. The pushing pressure is still less than the peak pressure which occurred near the start of combustion so it does not create the "overload" to the engine.


While the peak pressure in the cylinder has not been affected, the average pressure pushing on the piston over the entire stroke has doubled. This higher average pressure translates into more torque.

A properly designed turbo engine will be more drivable at low speeds than an equally powerful non-turbo engine with the same cubic capacity because the basic engine is more radical than a turbocharged engine.
 

A-R ratio is the ratio of the port diameter (A) to the port to housing radius (R).

 
 
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The point where the turbocharger starts to make boost depends on cam size, compression ratio, design of intake and exhaust manifolds and the turbo itself.  Different compressor housings have different compressor maps.  The maps of the compressor will show when and how the compressor will respond.  The lower the AR number (.42, .48, .6, .8 etc.), the less CFM it takes to make boost.  The disadvantage of too small of an AR number is that you will exceed the limits of the compressor at higher engine RPM.  There are only maps for the compressor housing, not the turbine. Turbine size selection is a variable based on RPM, the size of the engine, the weight of the car, and desired engine response.

Turbine power is used to drive the compressor and is varied by the A/R ratio and the wheel trim.  This will increase or decrease the power to drive the compressor for the desired response.
 
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For an example, a 2.8 engine using the T-3 with an A/R of .48 turbine and with a small turbine wheel, the engine will be at full boost at about 2400 RPM.  By the time you get to a little above 5000 RPM, the engine starts to quit pulling.
The exhaust pressure will go too high, and start to back up due to a to an undersized turbine housing and small turbine wheel.  To go to over 6000 RPM, a larger turbine housing is needed.  Changing the exhaust turbine from an AR ratio of .48 to .62 or using a larger turbine wheel or both will decrease the back pressure and solve the problem.  The result of this change is that the turbo will not make full boost until about 3300 RPM and run all the way through 6000 RPM.  Exhaust wheel trims (size of the turbine wheel) for a given a given turbine housing size will give the exhaust flow steps between the different size turbine housings.
 
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Please note that turbochargers such as T03, T04, and T70 are "family" names.  Within that family, there will be max air flows, and different boost characteristics.  There is no best turbo for any given engine because it depends on the driver, the cubic capacity of the engine, RPM range of the engine, and the volumetric efficiency.

For each turbo there is an option of different A/R ratios, different wheel trims and different housings for the compressor and turbine. These options will change the air flow and efficiency characteristics of the turbo to suite a particular application.
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Another important factor to having your turbo system functioning correctly is to have the entire exhaust system sized properly for the particular engine and application.  The header system to the turbo should be kept as small and short as possible to decrease the amount of turbo lag and wasted heat energy.  For the exhaust side of the turbo, it is important to keep the back pressure to a minimum.  A substantially larger piping system is needed to keep the back pressure as low as possible.  Smooth mandrel type bends are necessary on the exhaust side of the turbo to maintain low back pressure.

With the information we have given, it makes it very difficult to build a “standard” turbo kit.  Yes a standard kit will work but will the turbo system respond with optimum performance in the way the car is driven?  Most people don’t know how a good working turbo system should respond, so any turbo system will seem impressive.  The secret to having a good working system is to have proper fuel control, spark control and turbo size which will make or break a turbo system.

All of our systems are made in a fixture using the same engine/transmission combination that the customer is using.  All mounting hardware and the turbo system is test fitted before shipment.

 
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The turbo systems we produce are priced from $ 3000.00 to $6000.00 depending on customer needs.  The systems come with the air intake system from the air cleaner to the intake throttle body.  The ECU (stand alone computer) or a piggy back ECU (used in conjunction with your stock computer) is also included.  The exhaust system from the exhaust manifold to the tail pipe and all related hardware can also be furnished.

The customer will have to call WCF to discuss the specific needs of the turbo setup and installation to obtain pricing. Remember, each turbo system is manufactured to fit the customer’s specific needs.

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Copyright © 1999-2011 Erv Fleckstein ( West Coast Fiero ). All Rights Reserved.