View Thread: Turbo FAQ


SLP Addict
This is a article that was made by a friend, and co-owner of Lime Creek MotorSports(www.limecreekmotorsports.com)



What is a turbo?

- Essentially a turbo is an exhaust driven air compressor.

What does a turbo do?

- A turbo compresses air into the motor (aka creates boost)

Where is the turbo located?

- The turbo is located immediately after the exhaust manifold.

What does a turbo consist of?

- A turbo mainly consists of:
2 housings (compressor and exhaust)
center section (the lubricating and bearing section)
2 wheels (compressor and exhaust turbine)
shaft (connecting the exhaust turbine to the compressor)

How does a turbo work?

- Exhaust gases exit the cylinder and flow into the exhaust manifold. From there the exhaust gases are diverted towards the exhaust turbine where the combined heat energies and flow velocity spool the wheel. This in turn spins the compressor side of the turbo and it begins to ingest air and create boost.

What is in a turbocharger system?

- Turbo - duh!

- Wastegate - this is a spring loaded valve that opens and closes. It is responsible for maintaining turbine speeds and thus boost pressure. When it is open a good amount of the exhaust gas is diverted away from the turbine, hence the turbo does not spool. When it is closed the exhaust gas is directed towards the turbine and the turbo spools. These can be incorporated into the turbo (internal wastegate) or included in a seperate valve that is incorporated into the exhaust manifold.

- Exhaust Manifold - the design of the manifold is a key to lag reduction... it differs from a normal header in that it generally has short runners to maximize exhaust velocities and thermal energy. One key design factor that can describe the differences in inline 6 and inline 4 manifolds is the inclusion of exhaust pulses. To optimize a boost curve you want to use an equal length manifold system so that you aren't surging the exhaust turbine with 4 pulses per revolution. This can cause boost spiking and boost creep. Other design features are common to n/a headers like runner diameters, extraction, scavenging, etc.

- Intercooler - Compressing air creates heat. This heat is measured as boost temps. Naturally cooler air creates more power simply because it is denser and it allows more consumption of fuel. But the main factor to an intercooler isnt exactly the ability to create a little more power due to lower boost temps, its the fact that the lower boost temps allow more boost. Ex. SR20DET on stock intercooler can run about 10psi max boost before the intercooler becomes ineffective at cooling the extra boost. With a large front mount intercooler from Blitz the SR20DET can now safely run near 29.4 psi (2.0 bar) of boost provided the turbo and motor can hold up to it. A larger intecooler however will increase the area the turbo must fill before the system becomes pressurized... this when measured is refered to as "lag". An intercooler usually consists of bars and fins. Think of a radiator for air.

- Piping - Its piping... runs from turbo compressor housing to intercooler ... out intercooler to the throttle body.

- Downpipe and Exhaust - 3" or larger downpipes and exhaust optimize turbo breathing and allow for better heat extraction, spool up, and longer turbo life. Power also can be boosted considerably top end with a larger diameter system. Beware alot of the gains on a turbo car ... ex. 55whp on a Supra w/ downpipe addition is from boost increase, not the part itself. Generally a downpipe will create 1-3 psi more boost on a stock computered and controlled vehicle. Using a 3" downpipe on stock exhaust is not recommended as it can create boost spiking which can potentially damage a motor, especially if the rpms are low and the motor is still on its low fuel and ignition maps.

- Blow Off Valve (BOV) - Ahhh the ol' noise maker. Ever run a turbo car and hear the loud purge noise created when he/she shifted? Thats due to the BOV. The BOV is similar to the wastegate in operation. It has a vacuum line running to just after the throttle body to sense vacuum. What it does is when it senses strong vacuum (ex. when you close the throttle body in a shift) the valve opens and purges the boost withen the piping. This prevents compressor surging which will damage the turbo very quickly. Compressor surge happens because the turbo is still spinning when the throttle body slams shut. This causes the system to suddenly pressurize itself even more (if the BOV was non-existant or not working) and this surges the turbo causing it to slow down which exerts alot of force on the turbo shaft and other components. To prevent the valve from opening prematurely the spring tension is adjustable via a screw or bolt on top of the BOV.

Corallary to the BOV - Strong debates over weither or not venting to the atmosphere have been going on for years. Venting to the atmosphere on some cars tends to make them stumble because you have purged metered air and the fuel hasnt been purged. So when you blow off the engine suddenly goes rich and you get a nice fireball. Frankly there are no ET / MPH differences that I have noticed between the two. If you are having a stalling or studdering problem with venting atmospherically then you should look into recirculating the air back to the intake after the MAS.

What is Boost?

- Boost is a measurement (in psi) of the backup of air withen the manifold.

The Numbers

Name - There are a ton of turbos ... the name often refers to the size of the turbo. Ex. a T25 is alot smaller than a T88. HKS uses 4 numbers to explain their setups... ex. GT2835 ... this turbo uses a GT28 compressor with a GT30 Exhaust Turbine. Often the T## series turbos are Garret Turbos, such as the stock OEM Nissan turbos and the HKS Turbos. Greddy uses Mitsubishi turbos however and they often turn up as something like this, TD07-25G, this tells us that the turbo uses a TD07 housing and a 25G wheel.

Trim - Trims effect efficiencies... you could compair them to the duration of a cam. The trim effects boost temps and compressor air flow efficiencies at given shaft RPMs. The higher the trim the better the turbo operates at a faster shaft speed. Larger trim turbos such as a T04S (60-1) at highly efficient at higher boost levels but are crappy at lower boost levels, in fact you will hit the compressors surge limit at low boost as well as get boost creep. However a smaller trim will provide better low boost efficiencies. Keep in mind that the trim is a modifier on the compressor/exhaust wheels. Meaning it changes efficiencies at certain boost levels for the same wheel size.

A/R Ratios - Area/Radius Ratio... it describes the size of the housing. A larger a/r will make the turbo spool slower but will provide superior flow and thus more top end power. A smaller a/r does exactly the opposite, it spools the turbo quickly and provides semi-adequate flow. There are so many different a/rs out there that allow you to fine tune what you need out of a turbo.

Turbo Cooling

- Always opt for maximum shaft cooling... this would include water and oil cooling. This makes the turbo live alot longer.

Turbo vs. Supercharger...A few Differences

- Turbos are exhaust driven where as the supercharger is a belt driven device
- Turbos operate at much higher speeds generally ... unless you have some monster turbo
- Turbos can be controlled from withen the car ... no boost pulley change is needed to modify boost pressures

Turbocharging a N/a Car

- Say you have a JapTrap and you want to turbocharge it. Here are the basics to make safe boost.

- Turbo
- Manifold to fit turbo
- Downpipe to exhaust
- Piping
- Intercooler
- ECU Remap
- Larger Injectors
- Larger than OEM Exhaust
- Higher Flowing Fuel Pump
- Oil Lines and Water Lines for Turbo
- Misc. Fittings for Turbo etc.
- Intake for Turbo
- GOOD Hoseclamps
- Silicon Piping Connection Pieces
- Wastegate (if you arent using an internally wastegated turbo)
- Boost Control (Wastegate Spring, Electronic Boost Controller, Manual Ball Valve, etc. )
- By-Pass Valve or BOV
- Clutch
- Wider Tires ()

Car specific parts might include:

- Larger Fuel Rail
- Cutting

Controlling Boost

- Electronic Boost Controller - such as the Profec B from Greddy. What is does is control the wastegate which controls shaft speeds which controls airflow and boost pressures as a result. The EBCs control boost better than a ball valve which is a vacuum controlled device.

- I dont suggest any other method on the street but other methods are wastegate controlled boost and ball-valves aka manual boost controllers.

-Alan LaFrance
AKA Nismo_Freak

Rotary Boy
why did so few people check out my thread on turbo choice, and the turbo catalog from garrett?
a great link

here it is again (http://www.autoworldforums.com/vbulletin/showthread.php?s=&threadid=1468)

eric rxb
I looked at it. And i downloaded it. And I read through the catalog for a good 30 mins.

eric rxb
Blow Off Valves go :woowoo:

SLP Addict
Originally posted by Rotary Boy
why did so few people check out my thread on turbo choice, and the turbo catalog from garrett?
a great link

here it is again (http://www.autoworldforums.com/vbulletin/showthread.php?s=&threadid=1468)

This article is mroe for the noob.

89TTA
i wrote several turbo articles for ThongRacing.com, but no one would back me on the quotations from Corky Bell's book... so iunno if they're still there or if they're deleted or what... i'll try to find 'em...

SLP Addict
Cool, Just a reminder, if anyone has any articles that THEY have writte, please let me no, i would like to have as many tech articles as i can on ym site, you will be given credit, and if you have a website, you will be givin advertisment

Nismo_Freak
Corky Bell's book isnt that great... many people think its a Bible of Turbos ... I think it illustrates good points but is lackluster at best.

FYRHWK1
Originally posted by Nismo_Freak
Corky Bell's book isnt that great... many people think its a Bible of Turbos ... I think it illustrates good points but is lackluster at best.

Er, it laid out everything there is to turbos, are you sure you got it all? maybe you should read it through again. . .
The book was also written in what, 82? theres alot of new ways of doing things and technology that wasn't around then, the basics of it are still there, not a flame or anyhing, but i know I didnt get it my first time through.

kcg795
I'd like to get a turbo charger for my van someday. Not only do they sound cool, but it'd be nice to get a little extra HP and torque outta my little engine under my ass. But some mods may need to be done, like a new exhaust header. Also, my van has the MAF system. And there's a bunch of vaccuum lines hooked up to the throttle body as well. With a turbo, the vacuum the engine creates will be now positive pressure, meaning, it won't be a vacuum anymore. That won't affect anything, right? Or would I have to relocate the vacuum lines BEHIND the turbo?

FYRHWK1
Originally posted by kcg795
I'd like to get a turbo charger for my van someday. Not only do they sound cool, but it'd be nice to get a little extra HP and torque outta my little engine under my ass. But some mods may need to be done, like a new exhaust header. Also, my van has the MAF system. And there's a bunch of vaccuum lines hooked up to the throttle body as well. With a turbo, the vacuum the engine creates will be now positive pressure, meaning, it won't be a vacuum anymore. That won't affect anything, right? Or would I have to relocate the vacuum lines BEHIND the turbo?

Just get a simple vacuum pump, either blet or electric driven. alot of turbo cars do this instead of relocating the PCV valve to the turbos intake since the vacuum created is different. all your vacuum hoses can go there except things like vacuum timing advance, stuff like that would be thrown off by the constant vacuum created by a pump, not quite sure how you'd get around that.

kcg795
So, for things like the timing advanced, that can be installed behind the turbo then? What about the mass air flow sensor I have? Is there any modifications I can do so the engine won't need that? I notice some fuel injected engines don't have this device over the air cleaner box.

FYRHWK1
Originally posted by kcg795
So, for things like the timing advanced, that can be installed behind the turbo then? What about the mass air flow sensor I have? Is there any modifications I can do so the engine won't need that? I notice some fuel injected engines don't have this device over the air cleaner box.

the timing advance owuld be tricky, it would have to be placed before the turbo since after it therespressure, not vacuum. as to the MAF you can run it through there, he boost that is, only the MAF will be maxed and you'll need a fuel piggyback to tune with, otherwise your motor would run witht he wrong air/fuel ratios.