Turbo FAQ

Turbocharging is just another type of forced induction. That is, forcing more air into the engine, allowing more air for fuel to mix with for greater combustion. The same applies to superchargers and spraying nitrous oxide. They all just do it by different methods. Nitrous oxide has a higher percentage of oxygen than air, so basically you are spraying more oxygen into the engine than the normal intake would take in. A turbocharger or a supercharger adds air under pressure which increases the amount of oxygen per volume amount. Just to throw some science around: PV=nRT if volume (V) and temperature(T) are constant, than an increase in pressure(P) leads to an increase in amount of oxygen (n). That also goes to show you how temperature can add or reduce performance.

On another note: Frequently you see people designate the boost setting in lbs., psi, and Bar. This is the pressure above the standard atmospheric pressure of 14.7psi (sealevel). For conversion purposes: 1 Bar (barometric pressure) = 14.7psi 1 lb = 1 psi (lb/inch2)

So, if some one says they’re running 0.8bar: 0.8bar*14.7 = 11.76psi.

Due to combustion, we get exhaust gases. These exhaust gases flow out of the combustion chambers into the exhaust manifold. The turbocharger has two sides, a turbine housing (also known as the hot end) and a compressor housing (also known as the cool end). The turbine is placed in the direct flow of the exhaust gases which causes it to spin. This in turn spins the compressor which sucks in air (like an intake) and sends it toward the engine creating a certain pressure commonly measured in Bars or PSI. This is a simplistic explanation however. There are other optional mechanisms that can take part. They are provided later on in this FAQ.

The most basic parts to a turbo set-up are:
1. Turbocharger
2. Turbo Exhaust Manifold
3. 2 Oil lines: from oil pan to turbocharger and a return line
4. Charge pipes (to bring air from the turbocharger to the intake manifold)
5. Wastegate (to prevent too much boost)
6. Blow off valve (to relieve boost buildup in the charge pipe when the throttle body disc is closed)
7. Modification to the fuel system (dependent on use, explained later on)

You are better off talking to a professional on choosing a turbocharger because it is pretty dependent on what you are trying to achieve, how you plan to use the vehicle, and the specifications of the engine. Because we are interested in a small displacement engine ~100CID (1668cc), we would want to choose a smaller sized turbo. We want a smaller size because we only have a small amount of exhaust gas to spin the turbine. The smaller the turbine = lighter turbine wheel = less flow to make it spin faster. A T3, T25, or T3/T04 hybrid are three good choices in my opinion. There are other sizes as well. The T28 is placed size-wise between the T25 and T3. And larger than the T3 is the T4. The T25 is good but can get hot really fast and is usually only able to handle up to 14psi. The T3 and T3/04 hybrid are good because they can handle the low displacement, and a higher boost setting should you want to upgrade your setup sometime. T3 and T3/04 hybrids are among the most common turbochargers used. When talking about hybrids, it means that it has different parts put together from different families of turbos. A T3/T04 uses a T3 hot end and a T4 compressor. There are other hybrids such as the T25/28 and the T25/T3. The limits are really endless to build a hybrid. Another thing that has to be looked at is the A/R ratio. A smaller number generally is better for low end power, and a higher number is better for high end. For a mostly street and occasional race application I would suggest somewhere around a .48. For more high-end power, maybe a .63.

Some turbochargers have a water-cooling option. This prevents the oil from “coking” and the turbo from overheating. Plus, you don’t have to change the oil as often (~2000 miles regular, ~3000 miles with a water-cooled turbocharger).

Some turbochargers are Variable Nozzle Turbos (VNT). This is an awesome idea whoever came up with the idea. Just to put it simply, there are blades on the inside of the turbine housing. When the turbo starts spooling they are closed which decreases the volume of the housing and allows the turbo to spool faster. When it has spooled and the turbine gets fast enough, the blades open up, increasing volume, and allowing more flow for more power.

Another thing helpful in choosing a turbocharger, is using compressor maps. These are readily available from such manufacturers as Turbonetics Inc. This works like this:

You need to calculate your engine’s airflow at your target boost setting: Airflow (lb/min) = .2219 (RPM/HP)(1+Bar)

RPM = operating engine RPM This is where you want the power laid down HP= Naturally aspirated HP 1+Bar = The amount of boost (in bar) you plan on running + 1.

Plot Airflow on the x-axis (bottom for you special people) and 1+Bar on the y-axis (left side). Hopefully the lines intersect in the 60-70% efficiency region. If not, it probably isn’t the right turbocharger for you, so move on to a different one.

A wastegate allows excess exhaust gasses to bypass the turbochargers turbines so boost doesn’t “creep”. It allows the compressor to maintain a stable boost. Without the wastegate, the turbine could spin faster and faster with more exhaust gas flow, creating too much boost. Basically, when a certain pressure is reached, the wastegate vents off the excess pressure that builds up. The wastegate is also what is used together with a boost controller to limit boost.

BOV stands for "Blow Off Valve". When the throttle plate closes the engine still supplies a few extra pulses of exhaust gas to the turbo and the turbo still spins because of that and the inertial force of the turbine and compressor. This causes the turbo to compress the air in the charge pipes, but since the throttle plate is closed, this air has nowhere to go. The BOV opens up at a set pressure to ventilate this air to the atmosphere. The ventilated air can be routed back into the intake (before the turbo) to pre-spool the turbo after the throttle plate is closed and opened up again. This gives you a slight performance boost when shifting and letting off the gas between shifts.

Because a regular manifold doesn’t provide the correct flow that is needed to spin the turbine. More importantly, you can’t generally just fit a turbocharger on a regular manifold. A turbo manifold is about half the length of a regular manifold and it ends with a flange made to fit a turbo. Also, equal length exhaust pipes on the turbo manifold and smooth mandrel bends make for good flow so that you don’t get any hot spots and lose heat inside the turbo header. You want to exhaust as much of the heat from inside of the combustion chamber as you can to drive the turbo. You can also wrap the turbo manifold with header wrap to keep the heat within it. Then there are issues such as keeping the surface area of the turbo manifold as small as possible to preserve the heat within it until it reaches the turbo; the thickness of the pipes is also important. The thinner the gauge, the less heat it soaks up and therefore the less heat it looses. Then there are certain issues with turbo manifold materials; stainless steel holds heat better than plain old steel for example. Ceramic coating a steel manifold is a good cheap option though. Then there are separate issues with heat damaging the turbo manifold material itself, so you have to compromise between manifold integrity and heat retention.

It doesn’t matter. A D17 is a D17. They all share the same manifold bolt pattern. The only difference is that you need to relocate a catalytic converter after the down pipe for the LX/DX/HX. Basically, convert your car to an EX exhaust system.

The fuel pressure regulator and fuel pump are combined to a single unit located in the fuel tank. This means that they aren’t easily upgraded. Let me explain a returnable system first. A returnable fuel system pumps out a certain pressure. The fuel is brought to the fuel rail and the injectors allow what volume and pressure is needed based on the signal from the MAF or MAP sensor. The unused fuel is sent back to the tank through a return line. So, the extra fuel makes it to the rail and is readily available for the taking. A returnless fuel system pumps a constant pressure and is adjusted by the fuel pressure regulator only to allow what is needed. So a small amount of fuel reaches the fuel rail and it all gets used. In order to get the fuel needed to maintain a proper air-fuel mixture, there are a few things we could do. We could convert the system to a returnable fuel system which is expensive and time consuming. It will require a stand-alone fuel management system too. The most common and economical way of taking care of the fuel is to get a “piggyback” fuel manager like the GReddy E-manage, Haltech F5, Motec, etc. to intercept the signals from the various sensors and up the fuel delivery, and add the control of extra injectors if need be. The fuel injectors atomize the fuel and that optimum atomization is variable and depends mainly on the fuel pressure entering the injector and the time for which the injector opens. The ECU varies the fuel pressure and the injector pulse width (time for which it opens) based on the MAP sensor. Better atomization means a more complete burn of the fuel for more power and fuel economy and reduced emissions.

For an EX, most commonly people have been running 5-8 psi. The LX and DX have a lower compression so they might be able to handle a little higher. At 10psi our head gaskets blow out. Therefore head studs and a better head gasket might allow you to run even higher boost on stock internals with a good intercooler.

There are different types of boost controllers. Electronic boost controllers control the actuator on the wastegate by a solenoid. There are also manual boost controllers. These work by turning a screw that allows a certain amount of pressure to the wastegate. The wastegate activates based on how much boost pressure the turbo is producing. There’s usually a little tube running from right after the compressor housing to the wastegate. There’s a spring in the wastegate which holds the wastegate valve closed until a certain pressure. The manual boost controllers are placed in between the turbo and the wastegate and the wastegate spring is made as small as possible to allow the boost controller the largest possible adjustment of boost. Boost creep is a condition where the wastegate valve cracks open before the onset of full boost. This bleeds off exhaust gases that the turbo could use to spool up, so it takes a longer time for the turbo to spool up. This boost creep can be controlled with a pressure regulator valve and a pressure relief valve. The downside to a manual boost controller is that you have to get out of the car, open the hood, and turn the knob if you want to adjust the boost. An electronic controller allows you to do this in the car and most offer a fine adjust knob. All in all, I think it depends on laziness. I’m lazy… I’ll take an electronic one. Thanks.

By going further, I mean building up your turbo setup. Obviously you want to get the best flow possible. A good “cat-back” exhaust (2.25-3”) is a good idea if you don’t have one already. An intercooler would be a good idea. Gauges are especially good for monitoring your setup. A turbo timer is good if you are lazy like me, or generally in a hurry. An aftermarket clutch like ACT is good. Some internals will help you support higher boost settings without killing your engine.

An air/fuel gauge is good to keep an eye on your fuel system and make sure it is delivering the correct amount of fuel for the air that is inducted. An oil temperature gauge is important so you know that you aren’t running your turbo or engine too hot. A boost gauge is almost a necessity so you know how much boost you are actually running and making sure it corresponds with what the boost controller says. You could also go with a pyrometer (EGT gauge) to monitor the exhaust temperature. This usually helps you monitor if there is something wrong with air/fuel mixture.

It just allows you to take the key out of the ignition and let your car idle for an allotted amount of time. It does it so the turbo gets a chance to circulate oil as it cools down so it doesn’t have an instant “shock” from hot to cold, which lowers the life of the turbocharger. I would recommend one. They are relatively cheap ($100). The GReddy Full Auto Turbo Timer is good. It offers a speedometer, voltage meter, lap timer, and more. It also recommends a countdown based on how much you have driven, voltage, etc. It also has a safety feature so that if it is in countdown and the engine RPM’s go up, the engine will shut off.

An intercooler isn’t always necessary, but highly recommended. It adds power by cooling the air and prevents detonation. It cools down the hot air from the turbo in the intercooler, and sends it to the charge pipes. This allows you to run a higher boost setting because the charge is cooler and gives a less chance of detonation. It works exactly how a radiator works: convection. There are air-air and air-water intercoolers. On our cars, air to air intercooler piping is hard to route due to space, but it still can be done. Air to air intercoolers work by passing cool outside air through the intercooler, while the hot gasses are inside. The air cools the metal which in turns cools the charge. An air to water intercooler uses a “water jacket” to store the liquid. The air passes through the jacket cooling the liquid which cools the aluminum which cools the charge. It will require a separate pump to flow the water through. Water can stand, but there would be little or no benefit.
FYI: TMIC stands for Top Mount Intercooler and FMIC stands for Front Mount Intercooler.

Under a higher boost setting, more pressure is put on your transmission to deliver more power than it was originally manufactured for. This causes it to heat up and wear out fast. Also, the stock clutch simply won’t lock together past a certain torque setting. It’ll just spin and you won’t be able to accelerate. Basically, your torque output will be limited by your clutch’s torque holding capacity. You’ll want to estimate how much power you’ll produce with your turbo and buy a clutch that can hold at least that much power. ACT offers a clutch kit for the D17 engines. You probably want to stick with a street application for drivability purposes. As far as I know, the Xtreme is the best for this application. The part number is HC5-XTOO. OO means you are using your factory flywheel. You could also swap that out if you want.

It depends how high you want to go. You could lower your compression with different pistons. Arias offers custom fabrication. Some companies have them for out cars. You can upgrade your intake manifold to handle more pressure. You could get a block guard made for turbo applications. KMS offers the manifold and block guard for the D17. You could change the connecting rods. Valve springs, valves, head gasket… The possibilities are endless. But before you say that you want to run this incredibly high boost setting, you have to make sure you have a fuel system that is going to support it.

HAVE FUN! Boost your brains out!