Guys I've just had a new custom exhaust fitted yesterday. I've gone from a small-ish Y-pipe system to a 2.5" straight through dual system. The cars still on it's break in map tuned with osiris. Idle with the small exhaust was 14.5-14.8 AFR. Now with the bigger true dual it's idle AFR Is 16-17!

The driving AFR's are still ok. Cruise/ partial throttle is about 14-13afr. Boost is 13 down to 11.7 ( the boost is very low. 0.4 bar.)


Does the lean AFR sound like it could damage the motor at idle? The AFR's driving are fine for the break in map IMO.

 

No it won't damage anything. You might have hesitation and stalling but fuel trims may help after a little bit (automatically)...

 

Yeah the car runs great. The idle afr should not damage the motor with no load on It. I'm only drivin the car for another few weeks before it goes to have it's final map done. It spools alot faster now too!

 

Idle and even cruising those AFR's are fine, I ran my 240 at 15:1 for better gas milage around town, would have ran it even leaner but with Tomei 270 degree cams it needed a little more fuel to run smoothly. No reason not to keep idle and cruising AFR's in the 14-17 range depending on how your car runs. No reason to waste gas and these AFR's are plenty safe under vacuum and low load.

 

No way a cat back exhaust should affect the A/F that greatly...the ECU can adjust to most 'normal' conditions, but in your case it's not...sounds like a different issue to me, such as an exhaust leak.