If so which one would you reccomendI drive 44 miles a day on the thruway from to school and back
Lots of people have made the same mistake and wondered why their engine performed worse after the change. The source has a very good explanation of why you can expect poorer performance and fuel efficiency with a larger exhaust. What it boils down to is you want the exhaust to be the same size (including the same cross-sectional area through the passages of the catalytic converter) as the collector size. After the muffler you can go bigger but it makes no difference. Before Corporate Average Fuel Economy standards were introduced in 1978 many manufacturers used substandard exhausts - whatever was cheapest. CAFE changed the economics so even tiny improvements in fuel economy were worth a lot of RD and quite a bit of production cost. All modern cars are engineered to provide the best fuel economy they can get.
I will say it increase horsepower, but, you may actually see a decrease in fuel mileage. The reason for this is your opening up the air flow through the engine, which causes the vehicle to run lean. The computer will then adjust the fuel/air ratio by supplying more fuel to the injectors. Years ago I had a Trail Bike and I removed the stock exhaust and installed a Bassani Expansion Chamber. When I gave it the gas, it would cut out on me. I had to install the next Bigger fuel jet in the carb. It run like a wild bat out of hell then, but, it did use a little more fuel than before. Dodge Man below me is probably correct as I not as familiar with this car as he is. I did want to tell what I did on my truck with a 350 V-8. I converted from a Throttle Body Injection to Muti-Port and added a different cam and direct drive timing. To keep the headers quite. I installed FOUR Cadillac reverse flow mufflers, two on each side. I got both; more power and fuel mileage, but, for what this cost to do, I will have to drive many years to realize any profit from this conversion.
It might help a little, but it would need to be a full cat-back system, which for your car could get expensive. Generally a good intake filter like a KN is the best bang-for-your-buck. After that would be a cold air intake, as they help efficientcy a little more. Then, after either of those, if you still wanted to see more improvement I'd look into exhausts. I have a cold air, iridium spark plugs, and a cat-back exhuast on my Tuscani GTV6 wich is rated at 18-21mpg. I now get about 25mpg If I drive conservatively. *** PS you car has nothing to do with dual exhaust as it is either a inline 4 or VR6 motor. dual exhaust or true duals is a term used to describe two seperate exhaust paths coming from two seperate exhaust manifolds and is mainly just for bragging rights, as the performance increase over a standard system is little to nil. Every motor VW has ever put in any Jetta has only had one exhaust manifold so the concept doens't apply to your car anyway. Just thought I'd clear that up. PSS Snaglefritz answer below me is entirely accurate for his application, but there is a couple things that may be missleading. Primarily it is correct to say that a performance exhaust system will indeed allow you to burn more fuel, increaseing power and decreaseing economy. The difference is that it is a dirt bike, and is ridden at wide-open-throttle (racing) just about all the time. Secondly, it doesn't have an ECM to control fuel delivery. As he stated it uses a carb, which is a mechanical device that uses jets to determine fuel flow. In your Jetta however, the ECM computer can calculate that, thanks to your free flowing intake and exhaust, it can provide the same cruising speed (like your commute to school) while doing less work (delivering less fuel) as it has to work less to suck the air in and to expell it out. ) But yes, if you floor it you will go faster and use more fuel )
