External Wastegate – Whats it all about?

January 25th, 2022 by

The External Wastegate looks cool, but what does it actually do and what do I need to know?

An external wastegate is best described as a turbo bypass valve. The vehicle’s engine produces exhaust gas. The exhaust gas then flows through the exhaust manifold to your turbo where it pushes past the blades causing the turbine wheel to rotate. As the turbo rotates, it spins the shaft. And on the other end of the shaft is the compressor aspect of the turbo, and it sucks air in and pushes it back into the engine under pressure known as boost, this higher pressure crucially has a higher volume which allows the engine to add more fuel to create more combustion and more power. Good stuff right? YES!

But, (there’s always a but) the turbo needs control. Otherwise boost increases at a rate your engine and fuel systems cannot handle. To achieve this we use an external wastegate to vent exhaust gas around the turbo. Imagine your bathtub, the overflow stops the bath from getting too full. The only difference is we control the wastegate to alter how much water (boost) is in the bathtub.

External Wastegate

What about external wastegate sizes?

Now you know what the wastegate does, it’s important to discuss sizing. A common mistake is to assume that more power needs a bigger external wastegate. But this is not strictly true. If you have a large engine such as a 7.0 V8 built to suit over 1000bhp, but run a small G25 turbo on it. The chances are that you will actually run that turbo fairly hard and not need to bypass much boost. So a smaller wastegate is suitable. However, if you have a 2.0 litre 4 cylinder engine with a 1000bhp turbo, you will most likely find that even if the engine is built to be very strong the turbo will create way more boost than the engine can handle. In this instance, you need a very large wastegate.

Turbosmar External Wastegate

So which Wastegate do I need?

This depends on a few factors, and one very important factor is exhaust manifold design. More specifically the wastegate port. Our manifolds use a scooped port design precisely positioned in relation to the merge of the collector, this is to ensure as much wastegate priority as possible. We need this in a manifold design because if you cannot flow gas towards the wastegate then the wastegate cannot do its job and the dreaded boost creep will happen. Not all wastegate are created equal either. We base our production manifolds on Turbosmart external wastegate as in testing we have found this to perform the best on the market. We have a very good knowledge of what combination of wastegate and turbo to use with our manifolds. Please get in touch if you are unsure. [email protected]