Exhaust Back Pressure
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Elder User
Joined: Jul 2005
Posts: 659
Likes: 2
From: Berthoud, CO
Exhaust Back Pressure
I was driving down the highway the other day, and had my evolution hooked up and noticed the exhaust back pressure reading was 26 psi. This seems high to me. Where is the evolution reading this pressure from and is that a normal number? Hopefully one of you guys with an evolution will have an idea, thanks!!
Senior User
Joined: Aug 2004
Posts: 352
Likes: 0
From: Racine Wi
I do not have the evolution, but I do have the AutoEnginuity software. I also questioned the exhaust backpressure numbers recently. I had several folks test theirs as well as testing my own, and the "normal" reading ranged from 12.5 at idle to 52 PSI at WOT. Most ran at 49-52 at WOT. I was very surprised at this since most of us have 4" exhaust, but it was explained to me that this is the packpressure required to drive our turbos. Your reading is fine.
Jim
Jim
Lead Driver
Joined: Oct 2004
Posts: 7,413
Likes: 1
From: Columbia, MO
Exhaust size is not going to change the exhaust backpressure that much. The exhaust backpressure is affected more by the size of the turbo's exhaust housing. It takes it's readings from the passenger side exhaust manifold. You'll see a metal tube in the exhaust manifold that runs to the front of the engine, just in front of the HPOP resivoir, where the actual sensor is located. Your readings seem pretty normal for a stock turbo. The stock turbo has a backpressure to boost ratio of about 2:1. So, if you're running 25 psi of boost, you'll probably see around 50 psi of backpressure. Imagine how hard that is on the engine. That's another reason why the stock motor was limited to around 18 psi of boost. And, that excessive backpressure is also why I switched to the larger exhaust housing from a van turbo. It has a backpressure to boost ratio of about 1:1, up to around 35 psi.
