I understand how a simple turbo set up works.

Exhaust spins the hotside, through the spindle spins the cold side, draws in air, pushes through intercooler and into the throttle body.

When the ecu decides the turbo doesn't need to be engaged (idle, letting off accelerator etc) the waste gate is opened so that the turbo isn't spun anywhere near as fast.

Am i right so far?

How does the actuator work?

Diesels are negatively charged vacuum (? Eh)

What does the n75 do exactly ?

Anything I've missed?

The wastegate is opened once peak boost is achieved to prevent anymore boost being generated...basiclly it allows some of the gasses to bypass the turbine.

The actuator is the mechanism that controlls (open and closes) the wastegate

Diesel turbos dont use vaccum....im not 100% sure why that is and dont want to make anymore of an arse of myself than my spelling and grammer already has so il leave that there

Is the n75 the diverter valve? If so then basicly when the boost is no longer need it it simply diverets the pressure else where i.e. back into the intake pipe or vents to atmosphere.

Ohhh and anyone feel free to correct me if im wrong on anythinh

Ok, the actuator is basically a devices for opening the wastegate, it has a pre determined opening pressue which is set by a spring inside the actuator, pressurised air from the intake of the engine is applied to the acuator, so in effect it us a closed loop operation, turbo spins fast it makes boost which forces wastegate open which slows turbo down and so on, this effect also regulates the turbo free running speed.

all engines make vacuum naturally, petrol or diesel, until the turbo output goes above atmospheric pressure, then it is 'on boost', diesel engines dont have a throttle body, so likewise they dont need a recirculation or dump valve.

The n75 is a bleed valve, remember our wastegate actuator which is fed a boost hose from the intake manifold like i said earlier, the n75 sits in the middle of this hose, then the ecu will open and close the n75 roughly 100 times a second, so the acuator still only sees its pre determined spring pressure but the excess is bled off so the boost level rises at the manifold, the advantages are that the ecu can control boost pressure as per mapped requirements and its a failsafe to keep boost at low levels if a component fails.

THE ecu doesnt decide when the wastegate opens per se, its purely a mechanical closed loop process based on the boost pressure, but this is also based on how far you have opened tbe throttle.

the recirculation valve or dump valve is another device intake side to vent boost pressure when its not needed, its done when the throttle closes, excess boost overcomes the spring so the valve opens either to atmosphere or back into the air intake, this process stops the turbine from stalling, alliwing the turbo to freewheel if you like, which makes respool much quicker when the throttle is reapplied.

i should also say that this is just generalised info, modern engines have electronic control of some of these functions, also many modern diesels use variable geometry turbos which have no wastegate in the classical sense.

any questions just ask, hth.

Interesting read here, don't know anything really about cars as am new to this myself, so my question is, when people install a larger turbo to a vehicle is this for mass of air or simply pressure related?

Interesting read here, don't know anything really about cars as am new to this myself, so my question is, when people install a larger turbo to a vehicle is this for mass of air or simply pressure related?

both, they are directly related anyway, when a manufacturer chooses a turbo it will be closely matched to the operating parameters of the engine with a little bit on top for safety and durability, when you crank up the pressure quite often the turbine reaches its capacity of flow, in which case all that happens is heat rather than boost, so a larger unit is selected.. this has downsides too, a larger turbine has more rotational mass so it takes more time to get up to speed, hence lag.

Interesting read here, don't know anything really about cars as am new to this myself, so my question is, when people install a larger turbo to a vehicle is this for mass of air or simply pressure related?

Both really

 

good read here , quite technical but you can skip the maths

 

http://www.enginelogics.com/read-a-turbo-compressor-map/

Interesting read here, don't know anything really about cars as am new to this myself, so my question is, when people install a larger turbo to a vehicle is this for mass of air or simply pressure related?

 

As a general rule of thumb different size turbo's have different characteristics, the bigger they are the longer they take to spool up and get on boost on the plus side they can deliver bigger volumes of air at higher engine revs when the engine requires more air than a smaller turbo can deliver.That said a smaller turbo spools up quicker at lower engine revs but can't provide enough volume at higher revs "running out of puff" so to speak.

 

The boost control systems are key to a good install and Tom described the operation well. The boost control systems vary from very very complex to simple. You can run without any controls when the waste gate will open at its default setting which for a Scooby running a TD04 turbo is around 5psi. To do this you run a pipe from the inlet manifold to the actuator when boost hits 5psi the actuator opens. You can add a mechanical bleed valve to the same line and adjust it so it bleeds off some of the air pressure to the actuator keeping it below 5psi until the boost can't escape quick enough then opening the waste gate. You can vary the "bleed rate" to increase or decrease boost pressure. Not the best way of controlling boost but doable.

 

Instead of a bleed valve you can add a boost solenoid valve which does a similar thing though controlled by the ECU. You can also add a MAP which measures atmospheric air pressure and adjusts the boost accordingly to allow for variations. Boost pressure is relative to atmospheric pressure as it relates to the density of air..

 

Going back to the actuator control some systems can suffer from waste gate flutter at the point of opening when its not sure what it should be doing. A damper is added in the line on some systems to smooth out any fluctuations in air pressure when operating. Its essentially a little "pill" with a hole in it which restricts airflow.

 

Anyhow that's enough techno babble for nowI'll leave the rest to someone else.

http://en.m.wikipedia.org/wiki/Turbocharger

Ahh I see now the the purpose of an intercooler, cooler air being denser ie higher volume of air. Clever!

Cheers for info, may need to read up a little more before I begin modifying anything that intense on the furby though :p

Thanks for the info. And sorry it took so long to reply, i thought ny replied threads would come up in notifications.

I'll check out those links on my laptop later.

Im guessing you wouldn't be able to put a turbo off of a petrol onto a diesel due to the vacuum ? Or vise versa. Or would changing the actuatoe overcome this?

All just theory to further my understanding. I've got no plans to put a petrol turbo on a diesel lr vise versa.

No, forget vacuum, it makes mechanically no difference, the turbocharger from petrols and diesels are more or less the same except diesels run a much higher boost pressure, the higher pressure is the only reason why you would change an actuator.

Ah ok thanks for clearing that up.

So for instance i could fit a k04 to my 1.9tdi.forgetting about Oil pipe, exhaust manifold, exhaust, and pipework. It would spool and deliver the same as the std one. Obviously pressure, lag etc would be different ?