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2011' C30 running lean under boost

Help, Advice, Owners' Discussion and DIY Tutorials devoted to the second generation C70, S40 and V50 Volvos -- awkwardly model year 2004 ½ onwards -- plus where to go for advice and discussion on Volvo's sporty C30 Coupe powered by Volvo's ubiquitous inline 5-cylinder power plant.
TheScott
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2011' C30 running lean under boost

Post by TheScott » Mon Jul 25, 2016 2:41 pm

Hey guys!

The other day I had my car dyno'd and the car made the numbers as rated, if not better. But one thing we all saw as concerning was it's AFR. under boost, it held 14.7 AFR till redline. Generally, I thought turbo cars, these in special, should be around 11-12AFR under boost. Please correct me if I'm wrong but should I be concerned? The car is getting the Polestar update done to it on the 29th.

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Scott

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kcodyjr
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kcodyjr

Re: 2011' C30 running lean under boost

Post by kcodyjr » Thu Sep 15, 2016 12:31 pm

It's not running lean. It's right on the money.

14.7 is the stoichiometric ratio, the only AFR where all of the fuel and all of the air will be consumed. Any other ratio, and you will have leftover one or the other.

I would expect a modern engine to fight to maintain 14.7 like the hounds of hell were on its heels.

Historically, going rich under boost was a knock-prevention measure; literally wasting gas as a liquid in-cylinder coolant that's not intended to burn.
1997 850 GLT sedan, 152K and WHOOHOO!
RIP 1996 850 wagon, 201K, hit by a runaway 4-wheeler
RIP 1996 850 GLT sedan 5spd, 260K, rearended someone
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RIP 1981 242 turbo 5spd, 300K, serious teenage crash

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