Hey guys. So, after having put on the exhaust system (true dual) I got from Brassmonkey, and running a few sample tanks of gas, I seem to have lost mileage. Before, I'd get about 425 km/tank. Not bad, when measured with my Jeep. But now, I'm at about 375, and need to fill up tomorrow. No, my driving style hasn't changed. Any ideas? Everything else, sans the K&N filter is stock, although the plan is to port the manifolds, and ditch the AC and air pump/acv. Any help appreciated.

-Rick

 

Edit function is gone, sorry. Also, when I open up the S4 n/a LIM, how big can I make the manifold to block ports? Thanks.

 

Hey Rick

What exhaust did you have on the car before? Did you notice a performance increase with the true duals?

I'm not really sure what you mean by porting the intake, really the only thing you can do is port the TB and match-port the lower intake manifold to the block. Any gians done by this will be so insignificant you probably wouldn't notice.

 

The previous exhaust was the factory system. And yes, by porting the intake, I mean match-porting the ports. I just think its weird that I went from stupid restrictive to wide open exhaust and yet, worse mileage ensues. I did change the O2 sensor though, maybe that had something to do with it.

 

With a less restrictive exhaust, you may have lost torque at lower rpms in favour of higher rpm horsepower, and you may be delaying upshifts or using larger throttle opennings to compensate in regular driving. I noticed when I went to a less restrictive exhaust that on hills around Calgary that I used to be able to cruise up in 5th gear at say 80, I either found the engine straining to maintain speed, or I downshifted, or speed up to say 90 to attack the grade(and with some 800' in elevation difference between highest and lowest parts of the city, this is a fairly hilly town, so lots of opportunity to notice this). There's no question there's significantly more power at the top end, but with some loss of low end grunt.