Turbo FAQ

This FAQ was created to answer common questions people have about turbocharging. It was put together with information found all over the web and from previous questions.

What parts make up a basic turbo kit?
Most turbo kits come with the following parts, these are talked about in further detail later in this FAQ

Hot side exhaust
Turbocharger
Wastegate (If turbo does not have an internal wastegate)
Blowoff valve (if using moderate boost)
Silicone Connector pipes, Tbolt clamps
Intake piping, downpipe.
Boost referenced fuel pressure regulator

Optional parts are
Intercooler & Intercooler piping

Most kits do not come with fuel components, tuning software or wideband o2 sensors, all of which are a good idea for proper tuning.

What's up with methanol/alcohol/water injection?
Methanol injection is methanol (high octane fuel) and injected into the intake pipes, this helps prevent detonation when you are running on lower octane fuel and/or non-intercooled applications. Methanol injection systems can be had for a few hundred euros.
It can be mixed with water or run straight.

Alcohol is also a "high octane fuel" which helps suppress detonation like methanol, it to can be run straight or mixed with water.

Water injection cools the intake charge which allows you to run more boost with suppressed detonation.

What is "hot side exhaust"
Hot side exhaust is the exhaust piece(s) that bolt onto the heads and work their way to the turbo(s). These pieces can be purchased from several different kits if you are making your own custom setup or if you really want. Several members on here can make custom hot side exhaust to fit any application.

Parts of a turbo

Here is a basic cutaway image that shows different parts of a turbo, this image does not show the exhaust inlet which can be

seen under the Exhaust Turbine section of this FAQ

What is the downpipe?
The downpipe is a pipe that connects to the turbo on the other side of the exhaust turbine, this pipe generally connects to the factory exhaust system.

How is boost controlled?
The amount of boost generated by a turbo is controlled by a large valve called a Wastegate. The Wastegate is mounted on a flange that is generally welded onto the hot exhaust piece close to the turbo flange.

When boost reaches the desired level, a boost controller diverts pressure into the wastegate allowing the valve to open and vent exhaust gas out the other side of the valve, this prevents the turbo from spooling faster than it is already going and potentially slows it down some depending on how far the gate opens. There is a wide range of boost controllers manual and electronic available for fairly reasonable prices.

( Pictured : TiAL 46mm Wastegate )

Note : Some turbos have internal wastegates, which means the hot exhaust piece will not have a wastegate flange on it.

What is a blowoff valve?
Blowoff valves are to relieve pressure when your throttle plate closes, if your turbo is spooled up and pushing major air, and you let off the throttle without one, it can cause your turbo to backspin and cause excessive wear on the bearings. This valve is more important to cars with manual transmissions.

( Pictured : TiAL 50mm Blowoff Valve )

What is A/R?
The A/R of the exhaust is a ratio of the exhaust housing inlet area to radius. the smaller A/R will spool faster, but choke off sooner.
the higher A/R will spool later but make more power and higher in the RPM band.

What is the Exhaust Housing?
The exhaust side of the turbo is usually darker in color, this is where exhaust gas flows through the turbo to spin the compressor side. Inside the exhaust housing is a turbine, pictured in the cutaway view below.

( Pictured : Garrett GT42 Turbo )

What is the Compressor Housing?
The lighter, or polished in some cases side of the turbo, spun by the exhaust turbine this part of the turbo actually creates the pressure by spinning the compressor wheel.

When you hear people talk about the compressor turbine (or "compressor wheel") you might hear the words Inducer and Exducer size, here is a visual representation of what those are.

( Pictured : Compressor wheel, Inducer and Exducer labeled )

To find the trim of your turbo use the following formula
Trim = (Inducer / Exducer) ^2 * 100

( Pictured : Garrett GT42 Turbo )

Where can I tap and return oil on the FIRE engines?
There is a number of places you can tap and return oil on the FIRE engines, here are a few of them.

Tap Locations:
On the oil filter mount there is a bolt that you can get filtered pressurized oil from (top bolt since the bottom bolt is unfiltered).

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Return Locations:
Oil returns need to be someplace oil can drain back into your oil pan freely, it must be above the oil level in your oil pan, and below your turbo, remember that if you make this line hard to flow oil through, your turbo may have problems with seals in the future.

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The gravity oil drain line from a turbo should not be at any more than a 30 degree angle when leaving the turbo. With these engines the oil return can be almost straight down.

Who makes the "best" turbo kit?
Who makes the best cam? What is the best grind? Which turbo is best? None of these questions can be answered because each car owner has their own goals, so if your posting asking for help with kit selection do some homework instead of just asking which kit is best, and know what your goals are. Here are some things to consider while selecting a kit.

What is your horsepower goal?
Do you want to keep your A/C?
Do you have tuning software?
Are you willing to put the money into your fuel system?

How do I select fuel injectors for a forced induction application?
First you need to figure out what BSFC (Brake Specific Fuel Consumption) value you will use, BSFC is the pounds of fuel the engine burns per HP per hour.

Here are some BSFC guidelines.
.45 for N/A motors
.55 for supercharged
.65 for turbo

Injector Size in LB/HR = ((Desired Flywheel HP) * BSFC) / (# of cyls * Duty Cycle % / 100)

These simplified versions can be used for V8 motors with 80% duty cycle
Turbos : LB/HR = (Desired HP * .65) / 6.4
Superchargers : LB/HR = (Desired HP * .55) / 6.4

Example
600 * .65 / 8 * .80

Gives me
390 / 6.4

Result : 60LB/HR

For more information on this topic, see http://www.holley.com/HiOctn/TechServ/TechInfo/TchArtcl/Artcl07.html

Some good reading for the basics about turbochargers and understanding compressor maps
thanks to Jose (JZ 97 SS 1500) for this
http://www.forcedinductions.com/help.htm

What other things do I need when I boost my beast

You need the proper balance of fuel, air and ignition

The more air you put into your engine the more fuel you will need so bigger injectors and bigger pump are a must. After A LOT of power increase you will have to upgrade your fuel lines and fuel rails.

Tuning, you need to have it tuned properly
The only HP limit the FIRE engine see is tuning, no one that I know of have split their block because they made to much power, but I have seen a lot of times where they put a hole through their block because of poor tuning.

Drivetrain: you need to have stronger components to handle all that extra power your now running. You need a stronger clutch, built tranny, stronger driveshafts and differential.

Suspension: you have to put the power to the ground if you want to make use of it, so get your suspension worked out. Get a strong torque arm too, so it doesn't end up braking.

How much boost can I run
0-infinate Psi
basically you are limited to octane and timing, the more boost you use the more easily the mixture can pre-ignite (which causes knock), so you have to use a fuel that ignites on a higher temperature (aka higher octane fuel) or pull enough timing.
To give a ruff estimate most people use about 7psi on a stock compression ratio engine (9.1-10.7:1)
if you lower the compression ratio in your engine by larger combustion chamber heads, thicker gaskets or dished pistons, this will also allow you to run more boost on the given octane.

What size turbo should I use
http://www.forcedinductions.com/help.htm has a lot of good information on selecting a turbo that will suite your needs.
Basically you need to start by knowing your power goals. Select a turbo that will support that power level.
next where in the RPM range it makes its power is also important. This can tuned by selecting the A/R of the exhaust housing. the smaller the AR the faster the turbo will spool and make more power, lower in the RPM range, but will choke off power in the upper RPM range. A larger AR will spool later in the RPM range, but will make more power in the Upper RPM range.

Why isn't anyone running 30psi or more on a V8 engine like the imports do
psi or boost is resistance to flow
psi is irrelevant, how much air goes through your engine is important. A lot of people give an example of two straws one really thin, one large. If you blow into the small straw it is harder as the velocity of the air increases, but not a whole lot of air is moving. Switch to the larger straw, it is easier velocity is low but your pushing a lot of air through it.
These 346 cubed or larger engines flow very well so 15psi can make around 700rwhp.

How much power will I make if i'm running Xpsi or increase it xpsi?
There are a lot of variables and some other thing in contribution, but if you start out with what your engine makes NA
(0psi) you double the power at 1 atmosphere (14.7psi or 1 bar) so we can come up with a rough formula of
new power = [ ( NA power / 14.7 ) * amount of boost ] + NA power

Can I run a turbo on my high CR engine and low lsa cam
Not really, well yes but it wont do as well. With a higher CR then stock your going to have problems not running high enough octane, you will be fighting knock so you wont be able to use enough boost to make it worth your while.

The low lsa cam also isn't best for your turbo, it will bleed off boost and not give enough gas flow velocity till the upper part of the RPM range.

What cam should I use with my turbo set up?
There is a lot of debate here but first off the stock cam does pretty well. A higher lsa seems to be more desirable, this will bring the exhaust gas velocity up faster and spool the turbo more in the rpm range and not tend to bleed off boost. It needs to be matched to your setup also when you want the power to come on, and how high you plan on spinning your motor.
For the duration it needs to be matched to your engine size, intake and exhaust manifolds. The larger the engine the higher overall the duration should be. It was explained once to me that you want the intake duration larger then the exhaust that way you have a higher exhaust velocity which helps spin the turbo better.
Other theories have said that it depends on your headers, if you have a good flowing header that the exhaust duration should be greater then the intake, if you have an inefficient header that the exhaust duration should be lower then the intake duration. If you have a good intake and header set up they should be equal.
Id like to see specific testing so there could be definite answers.

What turbo kits are there for my Fire engine
Some have come and gone but here is a list (PM me if I missed any)

Autodelta single kits - Status unknown.

Vinci Motorsport single kit- Status unknown.

Smoketech single kit - to be released soon.

VanAaken single kit - Low boost kit in production, high boost version discontinued.

Should I go with a twin or single
Either or I don't believe in performance that it matters. As long as the exhaust to and from the turbo charger(s) are of equal efficiency both will spool the same (depending on the selection of the turbos) and make similar power if the right turbos are chosen.
if buying a kit, choose the one that will fits your needs.
if building your own, the things that should be the deciding factor should be packaging, ease of being able to work on it, cost, availability, weight.
Note a lot of race classes twins are outlawed. And most of the really heavy hitters are using a BIG single.
Most turbo companies say a twin is better for the street for good spool up, but the singles are more efficient on the top end with regards to racing.
some more reading, also talks about compound charging http://www.hotrod.com/techarticles/engine/113_0312_turbo/index2.html

What intercooler should i go with
you have two choices in IC's Air to water or air to air

which one is right for you.
generally people use air to air for the street and air to water for the track.
with the A2W IC you can put ice in the water box you can get the IAT down below ambient temperature. Member testing shows that A2W ic's with just water works well on the street.
A2A is a very simple design. With a properly sized core it will work well and generally be less expensive then a A2W. It will also do a good job on the street or track if properly sized