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Tuning turbo engines.
"A lot of hot air."
What is a turbo. If you go back to your childhood you probably remember those windmills sold at the seaside. Imagine a windmill with 2 propellers back to back.
As the wind blows the first propeller a shaft turns the second one and it will blow air in your direction.
A turbo contains 2 impellers which are located in the exhaust flow and along the intake path. The exhaust side rotates as the exhaust gases flow and this turns the impeller on the intake effectively sucking in fresh air.
So the turbo essentially generates power from the waste exhaust gases. Although sticking a propeller in the exhaust flow will reduce the exhaust efficiency the power gains on offer more than make up for this.
So who invented the the turbo? Aircraft running on fuel were altitude restricted due to the thin air and lack of oxygen this contains. By using a turbo the air could be forced into the engine and allowed the aircraft to run at higher altitudes or faster at lower altitudes.
It was not long before someone saw the application in car engines and we started to see turbos arriving in popular cars. In recent times manufacturers have been forced to produce more economical cars. With a turbo you get more power per cc making an engine more efficient. It is the power gains that TorqueCars members are most interested in, although the economy is nice to have.
Turbos allow small and light engines to produce the same power as a large engine twice its size but with lower fuel consumption.
The potential for turbo tuning power gains is massive. Most engines are over engineered for reliability and can take increases in power of 30-50%. Some engines can support even larger power gains. There is little surprise that in our 2 most tunable engines report, both are turbo driven.
With the advent of modern engine computer control we get a method of maximising the power produced by the turbo.
For example the exhaust gases are vented away from the turbo when certain levels of boost are reached. With a remap you can overcome this limitation. Fuel delivery also needs to matched to avoid running a lean mixture so the computer controls the timing and quantities of fuel delivery. Please review the articles on Remaps,BOVs, Boost controllers for more detailed information.
Are there any drawbacks to turbo engines? Until the exhaust gases start to flow quickly enough there is little the turbo can do. This is manifest in what is referred to as lag where the engine seems lifeless until the turbo kicks in. The bigger the turbo the greater the lag problem. Also when you compress air you heat it up and as we all know hot air carries less oxygen than colder air. This is easily solved with an intercooler.
No longer are we limited to a single turbo. Many cars now come equipped with Twin Turbos such as the GTO and Nissan 300zx. Big turbos are also on offer and this is the usual path an upgrader will take. We also see triple and quad turbo setups with boost controllers kicking in each turbo as exhaust flow increases for a steady power delivery.
Uprating turbos.
Adding a turbo to a standard engine is another option but there are quite a few considerations so read our turbo uprating article for a brief overview of some of the obstacles you will encounter.
Turbos are one of the best innovations in automotive engine technology.
They allow a small engine to produce similar power to much larger engines.
This enables the engine to be more efficient and with the move away from large V6 and V8 engines the turbo enables a manufacturer to build a car which has both economy and performance.
Your main aim in tuning a turbo is to enhance the airflow through the turbo. This applies equally well on the exhaust and intake side. Enlarging the intake channel and polishing the internal surfaces will dramatically reduce internal friction.
Many turbos and exhaust manifolds are cast and the casting process leaves seams and pits which dramatically affect air flow.
Using ball bearings instead of thrust bearings will allow the turbo to spool up more quickly. Ball bearings also last longer than trust bearings. Ceramic bearings have also been used for their heat resistant properties.
We should add that the larger capacity engines including the V6 and lazy V8's will produce phenomenal power gains if they were turboed as some of our serious drag racing members have discovered.
A 2.5 litre engine in NASP form will usually produce around 200-260 bhp. When the same engine is setup for a turbo we see power figures from 400 to 1000bhp.
Just a word of warning from TorqueCars - the turbo is spinning at 100,000's of RPM so be cautious when you switch off it needs oil if it is going to survive. If you switch off the engine whilst the turbo is hot you will burn off the oil inside the turbo causing excessive friction and wear.
Switching off the engine also stops the delivery of fresh oil. So allow the turbo to cool down by slowing up towards the end of your journey. Sadly people are generally ignorant of the oil and heat problem and will just switch off their engine after a spirited run.
Adding an aftermarket turbo to a car.
"Fully charged"
The basic reason for forced induction (turbo or supercharger) is not to increase compression or the maximum pressure in an engine cylinder, it is to increase volumetric efficiency (the efficiency of the engine at drawing in air) although forced induction is the most effective method of upping compression.
Put a turbo on an engine with an 10:1 compression ratio and watch it go bang!
Things to take into account when adding a turbo to a non turbo car (NASP or naturally aspirated engine).
When a naturally aspirated engine sucks air in, it can only draw so much in before the intake valve closes and seals the cylinder. The average N/A engine will pull in around 60% of its volume, so as a result is only 60% volume efficient. The more highly tuned an engine is the more efficient it will be, a typical Torquecars member will have already spend much time and effort tuning their engines but still struggle to get anything approaching 85% efficiency. The best way to improve this is to force the air/fuel mixture into the cylinders (forced induction) thus filling them more. The average forced induction engine runs from 110% to 150% volumetric efficiency.
Some examples of the result. a 2.0 N/A motor will use effectively around 1200-1300cc of its capacity. A turbo'd or supercharged 2.0 will use much more of it capacity, producing more power as it is able to burn more fuel. The more boost you run, the more efficient the engine hence we have 1.4 litre turbo engines producing as much power as large v6's. But the main benefit from increasing boost is to increase the final compression ratio and getting a better bang from the air/fuel mix in your cylinders (the actual engines compression ratio stays the same but as there is more air coming into the engine it will become more compressed).
If you increase the amount of air/fuel in the cylinders, then as a result you will increase the compression, which could be too much. In order to keep the final running compression the same, the initial compression (without boost) has to be dropped to compensate. More air will enable more oxygen to be available for burning and with the addition of additional fuel the engine will release more power. Turbo charging is the best way to increase the efficiency of an engine. When adding a turbo to an engine which was not originally designed for a turbo there are some major complications to take into account.
Detonation or knock - this is where the fuel ignites under pressure before the spark happens. This will cause a piston to move in the opposite direction if it has not reached the top dead center and will have disastrous consequences for the engine. As the intake valve will also generally be open the whole intake manifold, injectors and air filter will effectively carry the exhaust of the combustion and the movement of the piston in the wrong direction will cause internal damage and many components of an engine will be ruined.
To avoid this from happening you will need to lower the compression of the engine, and or restrict the turbo to a low boost threshold. (Low compression engines plus a turbo will also avoid some of the turbo lag problems inherent in most turbo applications.) The best turbos to add to a non turbo NASP (Naturally aspirated) engine are small. To lower the compression you can go with a re bore and fit lower compression pistons, you can add a stroker kit to alter the compression ratio or you can get a larger head and thick head gasket thus increasing the cylinder size and reducing the compression ratio. You need to aim for around a 7:1 compression ratio if you are adding a turbo, anything above 9:1 you will have problems. In all cases you should use the highest octane fuel that you can find as the higher the octane the more resistant the fuel is to engine knock.
If you can reduce the boost pressure to 5-7psi (as opposed to 25-35psi), and used the higher octane fuels available (e.g. Shell Optimax) you should be able to run a turbo on a standard engine with around the 9:1 compression ratio. For information on Octane and its effect on engine knock read our octane article.
When adding a turbo, for maximum performance gains, you should also get the head flowed increase the port size, fit bigger valves and go with a larger exhaust header and system as there will be a much larger volume flowing through the engine. Fitting a boost controller will allow you to experiment on a rolling road while attached to diagnostic equipment to find the optimum boost pressure.
Particular attention should be paid to fuelling. More air requires more fuel or you risk the danger of burning too lean. You also want to avoid overfuelling when the boost from the turbo drops as this can destroy the engine. On most turbo applications it is not likely that the cars existing fuel delivery system will be able to deliver sufficient fuel so you will need to uprate the fuel pressure with a new pump and fuel pressure regulator, the injectors will also need uprating. The car computer will also need to take into account the new fuelling requirements of a turbo, especially with regard to throttle position and wastegate control and rapidly changing fuel requirements between on and off boost conditions.
Most kits contain only the necessary parts to physically get the turbo onto the engine such as an exhaust header and the necessary intake plumbing to the air filter.
Turbos are expensive but will add the most power for your money. You should allow about 40 hours for fitting.
Source from : www.torquecars.com
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