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Author Topic: Free Flowing Exhaust Effects on a Turbocharger  (Read 690 times)
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« on: July 21, 2018, 11:51:48 AM »

I have a 2008 Audi A4 with a built motor , custom tubular manifold, 3 inch exhaust no catalytic converter, equipped with an external wastegate(14psi Spring). When I first started driving the car and attempting to tune it, I noticed that I didn’t have much control over the boost (overboosting, jerky, inconsistent, temperature based inconsistancy, etc). One day I added a catalytic converter and I noticed the boost was much lower, the spool was slower and the boost never went over 22 psi. At that time I was upset about how much slower the turbo spooled and I couldn’t wait to remove the catalytic converter. I adjusted the duty cycle and got the turbo boosting over 25 psi again.

Last month I removed the catalytic converter and now the car overboosts again. I believe I came up with a reason of why the car is overboosting. On Turbosmart’s website they mention that the wastegate cracking pressure is higher on the bench then on a car with backpressure. My theory is since I don’t have a cat, my downpipe, and exhaust are 3 inches, there isn’t much backpressure acting on the valve to assist with opening the wastegate(the car is totally dependent on diaphragm pressure only to open the valve). It is my opinion that lowering the spring pressure will  allow the N75 to control the boost better. Does this sound accurate?

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