Internal or External?

[YelloEye]

Well since we don't have a FI section in here I figured this would be the best place to start this thread.

I'm new to the whole turbo idea insofar as wastegates, BOVs and overall turbo efficency goes. So what are the differences in getting a turbo that has a wastegate built in or getting one that mounts to the manifold? I realize the physical differences, but what about the performance side of things? Reliability?

 

[USMCFieldMP]

http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech101.html

Wastegates
On the exhaust side, a Wastegate provides us a means to control the boost pressure of the engine. Some commercial diesel applications do not use Wastegates at all. This type of system is called a free-floating turbocharger.

However, the vast majority of gasoline performance applications require a Wastegate. There are two (2) configurations of Wastegates, internal or external. Both internal and external Wastegates provide a means to bypass exhaust flow from the turbine wheel. Bypassing this energy (e.g. exhaust flow) reduces the power driving the turbine wheel to match the power required for a given boost level. Similar to the BOV, the Wastegate uses boost pressure and spring force to regulate the flow bypassing the turbine.

Internal Wastegates are built into the turbine housing and consist of a “flapper” valve, crank arm, rod end, and pneumatic actuator. It is important to connect this actuator only to boost pressure; i.e. it is not designed to handle vacuum and as such should not be referenced to an intake manifold.

External Wastegates are added to the exhaust plumbing on the exhaust manifold or header. The advantage of an external Wastegates is that the bypassed flow can be reintroduced into the exhaust stream further downstream of the turbine. This tends to
improve the turbine’s performance. On racing applications, this Wastegated exhaust flow can be vented directly to atmosphere.

Internal wastegates are nice for lower boost applications... and can be used on high boost applications on smaller turbos. One of the major disadvantages of an Internal Wastegate is Boost Creep (Links for Boost Creep:What is Boost Creep; Boost Spike vs. Boost Creep)

Boost Creep: While boost creep also refers to an unwanted rise in manifold pressure, its cause and effect are totally different from those of spike, as is the way it manifests itself.

As you know, boost pressure is controlled by the wastegate, which allows exhaust gasses to bypass the turbine wheel. In effect, it creates an alternate route for the hot exhaust coming out of the motor to take, which means that any gas passing through it will not spin the turbine wheel.

Now, if this wastegate cannot flow enough to bypass the required amount of exhaust, then that means that too much of the gasses are going to go through the turbine wheel, meaning that it will have too much energy imparted on it (it will be spinning too fast). As the excess exhaust gas amount gets greater and greater, the turbine wheel spins faster and faster, and the boost level rises.

Creep happens ANY time when the wastegate cannot bypass enough exhaust gas to keep the boost under control. This can happen when the wastegate is too small in diameter, or when the design of the wastegate doesn't allow it to open enough, or when the wastegate simply doesn't have a good enough flow path to divert a lot of exhaust. It can also happen when you increase the amount of exhaust coming out of a motor (running more boost/airflow, making more power).

Since this tends to get worse and worse as the engine speed rises (more cycles per second is more conducive to more exhaust gas, to a point), that means that one will see the boost climb to the preset level on the boost controller, and then it will gradually creep up past that line to a "minimum" given the circumstances.

That minimum can be 2 psi above the set boost level, or it can be over 30 psi, depending on how the wastegate is designed, how big it is, the car's setup, and more.

It is also important to not that you certainly can have spike AND creep at the same time, which would result in the boost level jumping up, settling to the preset level, and then slowly climbing back up again as you approach redline.

 

[YelloEye]

Dude, thats exactly what I was looking for thanks. And glad to see you made the switch.

+1 inviso rep

 

[Zdeuce4]

i was told by shops that external wastegates hold boost better. from what i just read didnt it say internals hold it better?

 

[USMCFieldMP]

i was told by shops that external wastegates hold boost better. from what i just read didnt it say internals hold it better?

I don't know where you THINK you read that at... but you must have been dreaming.

And just like any other car part, the wastegates performance is based on the supporting parts around at, as well as whether or not it is properly sized. Too small of a wastegate on too big of a Turbo will cause Boost Creep. Too small of piping to/from your wastegate can/will cause Boost Creep.

But, Internals are more prone to boost creep than a good external.

 

[TurboTechRacing]

I don't know where you THINK you read that at... but you must have been dreaming.

And just like any other car part, the wastegates performance is based on the supporting parts around at, as well as whether or not it is properly sized. Too small of a wastegate on too big of a Turbo will cause Boost Creep. Too small of piping to/from your wastegate can/will cause Boost Creep.

But, Internals are more prone to boost creep than a good external.

Yup X2

 

[Zdeuce4]

I don't know where you THINK you read that at... but you must have been dreaming.

And just like any other car part, the wastegates performance is based on the supporting parts around at, as well as whether or not it is properly sized. Too small of a wastegate on too big of a Turbo will cause Boost Creep. Too small of piping to/from your wastegate can/will cause Boost Creep.

But, Internals are more prone to boost creep than a good external.

i may have wrote that incorrectly but i wasnt trying to say that an internal wastegate is better than an external, i mean shoot,im running external

 

[BlackCobalt707]

Time to switch setups

 

[n0xid]

External, and let it scream

 

[YelloEye]

Old thread is old....