Subaru WRX/STI turbo charger basics

When do I go with an external wastegate? External wastegates and when to use them have become some of the most commonly asked questions in the turbo business over the past year. External wastegates move the wastegate vent from inside the turbine housing of the turbo to a remote location, fed from the same tube (or uppipe) as the turbine inlet for the turbo.

There are several advantages as well as drawbacks to this setup. The first, and in many cases, the drawback that discourages most Subaru owners, is the cost. Not only are you adding expense to your turbo upgrade through the wastegate assembly, (normally starting at about $200) but there is also the additional cost of custom piping. Due to the design of the Subaru, it is more difficult than many vehicles to install/fabricate piping for the external wastegate units. This normally adds another $100-$200 in labor costs from a good exhaust shop.

There are companies now offering custom uppipes with flanges for the use of external wastegates, however, due to differences in input flange on different wastegates, these are not universal. The biggest advantage to the external gate setup is boost control stability. In very high horsepower cars it becomes necessary to have a large enough port for wastegate venting that it is simply impractical to attempt the use of an internal setup.

The larger external units will be able to hold the boost pressure more stable, and require very little actuation to vent fully and stop boost increase. It is this benefit that many times causes a vehicle with an external wastegate to produce additional power over an internally gated turbo, and is how the external has become known to produce more total power. Normally with proper turbo design and proper tuning, externals are not actually needed until power ranges rise into the 600 or greater HP range on a single turbo setup, and 900 or greater HP on twin turbos.

Are there any downsides to turbos?

There have not been significant amounts of problems with turbos. The main downside to turbos in general is uneducated usage. Careful planning, purchasing, supporting modifications, and tuning should allow the end user long and happy usage. Too often, many users take shortcuts, exhibit poor planning, or disregard necessary precautions and end up with disappointing failures.

Another downside is poor selection which leaves the user disappointed as the new turbo’s characteristics don’t meet their expectations. The two main disappointments are:
a. Not enough power
b. Incorrect spool characteristics for autocross and daily drivers

Which manufacturer is best? This topic is highly debated. There are just too many factors to consider. The main category breakdowns are:
a. Price
b. Performance characteristics
c. Warranty
d. Compatibility with end user’s desires
e. Bolt on or custom fabrication installation

 

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