Vvti Engine

[jakeyseven]

Why Have Vvti Engines Not Got Egr Valves Cheers Daz

[TrdSpeed140]

because they've timed the exhaust cam in such a way that, coupled with the factory exhaust back-pressure, some exhaust gas actually re-enters the cylinders just before the exhaust valves close at the very beginning of the intake stroke. changing the factory exhaust system changes the way the exhaust flows, which can cause less exhaust gas to be recirculated back into the engine which is why you may see a slight decrease in fuel economy with an aftermarket exhaust system. hope that helps.

[20SilverStreakin07]

Originally Posted by TrdSpeed140

changing the factory exhaust system changes the way the exhaust flows, which can cause less exhaust gas to be recirculated back into the engine which is why you may see a slight decrease in fuel economy with an aftermarket exhaust system. hope that helps.

So would it be safe to assume that putting a performance exhaust system (headers, cat delete, cat back system etc,etc...) would actually decrease performance rather than increase it dealing in terms of mpg? I would think that if you kept the cat converter it would be sufficient enought to keep a certain amount of backpressure to go back into the cylinders. I was thinking about doing some mods to the exhaust system to get the engine to "breathe" a lot better. Now, I'm not so sure. Hmmm, interesting....

[TrdSpeed140]

there's always that trade-off with changing stuff like that. you lose a little mpg but gain a few ponies, honestly, it loss of a few mpg from just changing the exhaust isn't gonna make me lose any sleep, it's just something to think about. there will always be at least a little back-pressure (unless you've got a 3" straight-pipe setup or something). If you're gonna be upgrading the exhaust then my advice would be to stick with 2.25" or 2.5" (max) diameter piping and get a good hi flow cat-converter, a decent length resonator and a good oval muffler. that will keep the annoying raspyness down and give you a nice throaty tone.