Project Evo X , Testing The AMS “Widemouth” Downpipe!
By Mike Kojima
When we last left off with Project Evo X we had tested the K&N Tsunami Intake and Greddy RS exhaust with good results. Continuing with our testing of easy bolt on engine parts, the next step in uncorking our car was to go further upstream in the exhaust with an AMS Wide Mouth downpipe and test pipe.
Since we opened up the back part of our exhaust with Greddy’s 85mm in diameter RS catback exhaust system, it was natural to next look for a better downpipe. After evaluating what was on the market, we decided to use the AMS Big Mouth because of several unique design features which we felt made it stand out above the rest.
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| The AMS Widemouth downpipe is truly a work of art. AMS used expensive investment casting tooling to build a thin wall cast stainless downpipe/turbine outlet to produce the freest flowing least restrictive downpipe on the market. The downpipe is compatible with the stock heat shields and is actually better than OEM quality! |
The turbine outlet on the stock Evo X turbo is a cast piece with a rather complex geometry. It hugs the back of the turbo pretty tightly and has a small diameter outlet, necking down to around 2.25” before it enters the actual downpipe. The discharge from the turbo’s internal wastegate is introduced right at the point where the exhaust flow exits the turbine and the entire gas flow is then forced to make a tight turn all in a small area.
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| You can see how the stock turbine outlet makes a very sharp turn right at the turbine and wastegate discharge. The AMS part uses smooth flowing bends with a much larger radius in this area. The area where the turbine and wastegate flow comes together is very critical for overall flow. Dumping all of this into a restrictive convoluted part is not the greatest for power. |
This creates a lot of turbulence and if the exhaust gas volume is increased by running other power increasing mods, this juncture is an area where a lot of backpressure will be created. Due to the space constraints, it is real hard to design a low backpressure fabricated part to fit in the area allowed that is actually better than stock.
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| Looking down the throats of the stock part on the left and the AMS Widemouth on the right, it becomes painfully obvious which part is going to flow better. You can see the complex geometry of the downpipe's inlet and how a casting is going to be able to make the most of the limited space here to make a good flowing part. |
AMS came up with a solution to reduce backpressure and improve flow in this tight spot by designing the Widemouth downpipe as a one piece investment casting. By making the turbine outlet section a casting, AMS was able to maximize what they could do in the area using three dimensions to make a higher volume, straighter path from the turbine housing to the downpipe itself.
