[Winkty]

Internal vs External Wastegate


Wastegates work kind of like a relief valve. They provide another path for the exhaust gases to flow.(instead of flowing thru the turbo) A turbo spools because of heat, pressure, and flow created by exhaust gases...so if you divert the exhaust gases to somewhere else besides thru the turbo (back to the exhaust, post turbo or atmosphere)...it will spin the turbo shaft slower and make less boost. Go it?

Now lets talk about how they open. Almost all wastegates use springs to hold the valve shut. There is also a boost reference line (typically run from the compressor housing of the turbo) that is connected to the wastegate which will open the wastegate valve (via a diaphram) at a specific pressure. The pressure that the wastegate opens at is determined by the spring we already talked about. If the spring is stiffer (harder to compress), it will open at a higher PSI....if it is softer (easier to compress), it will open at a lower PSI. That's why they sell springs for wastegates according to PSI. For example - If you buy a wastegate with an 8 psi spring...once the turbo makes 8 PSI...the boost reference line will show 8 psi at the wastegate and open the valve. When it gets below 8 PSI, the valve will close until you make that PSI again. The wastegate will constantly regulate the spooling of the turbo so that you make a solid 8 PSI the whole time.



External Wastegates - Most external wastegates use a piston style valve in them to regulate the flow of exhaust thru them. Typically these are a larger diameter and better flowing design than the internal wastegates. For this reason, external wastegate are better at controlling boost...more so at higher HP levels because of flow. Ext. wastegates are also typically more durable than internals because of the build quality and materials used. Another thing is Ext. wastegates can be vented to the atmosphere (via a dump tube) or back into the exhaust. While venting the wastegate to the atmosphere is a great flowing (and normally easier) solution, most people don't like it because of the "wide open" exhaust sound. When the wastegate opens, it will sound like you don't have much of an exhaust anymore. This is a GREAT addition to a turbo setup if you have the money.


Internal Wastegates - There are a few things that are different about internal WG's. First, they use a "flapper" style valve in them instead of a piston type. The "flapper" valve is typically mounted directly on the exhuast housing of the turbo which makes them ONLY dump/vent into the exhaust. They typically don't flow as well as external style. They also use an externally mounted actuator (which sometimes causes fitment issues in the car) to open the wastegate valve. It still uses a diaphram type of opening mechanism, but probably doesn't use the higher temp materials the external does. (because the external is mounted directly on the manifold normally and takes a lot of heat) Internal wastegates are normally perfect for cheap, reliable boost control. Factory cars have been using them for years. I think they work very well for low-mid boost applications. (my opinion)