Exhaust mods... better fuel economy ?


I just took out the rear mufflers to see what it sounds like.... it sounds like a cop car when its idling.. not loud, maybe a tiny bit of drone but easy ok... I decided to drive it around for a few days and to my disbelief the fuel computer is telling me its getting 10% better economy on the highway. Normally sitting on 120kmh it gets around 10L per 100km.... After a 315km highway run it was reading 9L per 100.... and, its 315km to my mums... 630 return... plus about 20km driving around up there. I have never been able to drive there and back on one tank sitting on 120kmh but when I got there (315km) it was telling me there was 350km left... It has NEVER even come close to that... So the exhaust is exiting immediately after the 2 center mufflers.
its telling me Im using less throttle to get the same speed...
Is it possible that this is really happening ?.. Is it possible that 10% of the fuel is being used to push the exhaust out the rear pipes and mufflers ?


New Member
Yes, that is absolutely correct, there is less resistance on the way of the exhaust gases, and this is the reason why they use straight pipe exhaust in autosport. Exhaust gases easily flow through as they don't have to go through the muffler tubing. Technically if you remove the catalytic converter it will give you even more power and fuel efficiency as a result, however it is not legal and not environment friendly.

Another step to improve your fuel economy would be adding the a performance air intake. This way the air will flow faster to the engine and go directly out with no resistance. It's actually described in this article: Can an Air Intake System also Increase My Fuel Economy?
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Yes, but your theory is correct on performance gains but only if I re-calibrate the fuel mapping.. I think the engine behavior is already starting to show signs of running lean... i have an air/fuel gauge and there is already a bung which I put in ages ago. I also have a Jaycar digital fuel adjuster which I built years ago but never used it... Ive gotta get the car registered in 2 months so I'll wait till then (as it has to be inspected as it has interstate rego) ... I want to go 2.5" single system starting after the front resonator....