Turbocharging

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Page created by T Jan 23 2007,

submissions by John (Arsewipe):
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Many dollars spent on lots of after market components. Click to Enlargen. Image by John (Arsewipe).
 

Turbocharging:

Theory:

Click to Enlargen. Image by V-EIGHT.

Turbocharging forces compressed air into an engine to achieve improved engine performance and fuel efficiency, with reduced exhaust emissions.

Operation:

The turbocharger is driven by waste exhaust gases, forced through an exhaust housing onto a turbine wheel. The turbine wheel is connected by a common shaft to a compressor wheel. As the exhaust gases hit the turbine wheel, both wheels rotate simultaneously. Rotation of the compressor wheel draws air in through a compressor housing, forcing compressed air into the engine cylinder.
The increase in air fed into the engine creates more combustion force and power.

Disadvantages:

Click to Enlargen. Image by V-EIGHT.
Not without disadvantages;
One of the main problems with turbochargers is that they do not provide an immediate power boost when you hit the throttle. It takes a second or two for the turbine to get up to speed before boost is produced. This results in a feeling of lag when you are waiting for the boost to happen, and then the car lunges ahead when the turbo gets moving.
One way to decrease turbo lag is to reduce the inertia of the rotating parts, mainly by reducing their weight. This allows the turbine and compressor to accelerate quickly, and start providing boost earlier. One way to achieve this is to make the turbocharger smaller. A small turbocharger will provide boost more quickly and at lower engine speeds, but may not be able to provide much boost at higher engine speeds when a really large volume of air is going into the engine.
A large turbocharger can provide lots of boost at high engine speeds, but may have bad turbo lag because of how long it takes to accelerate its heavier turbine and compressor.

Wastegate:

Click to Enlargen. Image by V-EIGHT.
Most automotive turbochargers have a wastegate, which allows the use of a smaller turbocharger to reduce lag while preventing it from spinning too quickly at high engine speeds. The wastegate is a valve that allows the exhaust to bypass the turbine blades. The wastegate senses the boost pressure. If the pressure gets too high, it could be an indicator that the turbine is spinning too quickly, so the wastegate bypasses some of the exhaust around the turbine blades, regulating the pressure supplied to the turbine.

Bearing Types:

Some turbochargers use ball bearings instead of fluid bearings to support the turbine shaft. But these are made of extreme materials to handle the speeds and temperatures of the turbocharger. They allow the turbine shaft to spin with less friction than the fluid bearings used in most turbochargers. They also allow a slightly smaller, lighter shaft to be used. This helps the turbocharger accelerate more quickly, further reducing turbo lag.

Turbine Blades:

Click to Enlargen. Image by V-EIGHT.
Ceramic turbine blades are lighter than the steel blades used in most turbochargers. Again, this allows the turbine to spin up to speed faster, which reduces turbo lag.
Some turbos, (Nissan), have plastic compressor blades to futher reduce weight.

Dual Turbochargers:

Some engines use two turbochargers of different sizes. The smaller one spins up to speed very quickly, reducing lag, while the bigger one takes over at higher engine speeds to provide more boost. EG: Nissan GTR

When air is compressed, it heats up; and when air heats up, it expands. So some of the pressure increase from a turbocharger is the result of heating the air before it goes into the engine. In order to increase the power of the engine, the goal is to get more air molecules into the cylinder, not necessarily more air pressure.
Mock fit up of new turbo and manifold, before fitting exhaust wrap.
Click to Enlargen. Image by John (Arsewipe).

Intercoolers:

An intercooler or charge air cooler is an additional component that looks something like a radiator, except air passes through the inside as well as the outside of the intercooler. The intake air passes through sealed passageways inside the cooler, while cooler air from outside is blown across fins by the engine cooling fan.
The intercooler further increases the power of the engine by cooling the pressurized air coming out of the compressor before it goes into the engine. This means that if the turbocharger is operating at a boost of 7 psi, the intercooled system will put in 7 psi of cooler air, which is denser and contains more air molecules than warmer air.
With any high performane engines, you need money, you are looking at around $5000 worth of upgrades, including electronics, and that is just bits that bolt on, no engine mods!!!
Click to Enlargen. Image by John (Arsewipe).

Pinging, Detonation and Pre-Ignition:

With air being pumped into the cylinders under pressure by the turbocharger, and then being further compressed by the piston, there is more danger of knock. Knocking happens because as you compress air, the temperature of the air increases. The temperature may increase enough to ignite the fuel before the spark plug fires. Cars with turbochargers often need to run on higher octane fuel to avoid knock. If the boost pressure is really high, the compression ratio of the engine may have to be reduced to avoid knocking.
Other things can be done also to address this problem, like an intercooler, water or methanol injection, etc..
I like the idea of using a Nitro/Methane mix, (Petrol R/C car fuel), as this fuel contains a high oxygen content and therefore will aid in a more complete combustion of the fuel mix, while having the added bonuses of cooling the fuel/air charge, and being a highly volatile mix itself. :)

I will take individual photos of specific components over time and add them with descriptions when I get time,
Cheers for now.
John
186S Engine with Garrett-Normallaire Strata II turbo kit with 2 175CD carbs. Click to Enlargen. Image by Mick.
 
HIF type SU Carburettors with Garret Strata II, TO4E 12 psi Waste Gate Turbo Charger. Click to Enlargen. Image by V-EIGHT.
 
Stromberg CD Carburettors with Garret TO4B Turbo Charger. Click to Enlargen. Image by A Holden Van.
 


SU Carburettors 

Links:

John (Arsewipe's) Shed

V-EIGHT'S ShedGarret Thread 1


Garret Thread 2

Hiy_po's Shed

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