Does Exhaust Backpressure Increase Performance?

I know a lot of people say exhaust back pressure is needed and you will get better performance with a muffler rather than just a straight pipe (I don't mean a muffler delete on a clapped out civic kind of straight pipe), but on that same note if there is less restriction to flow the engine can breathe more and in turn more power. So what is better, I know high performance drag cars run a straight pipe and so do multiple other high performance cars do. Is there an advantage to having back pressure in turbocharged systems or better for NA systems? Is it something to do with temperature and cooling? I just want to know what everyone thinks and maybe figure out this personal myth of mine.

As far as horsepower goes you don't need any back pressure as it reduces Volumetric Efficiency thus reducing engine power output. It's a myth that engine needs some back pressure for power - something like the saying that "horsepower sells cars but torque wins races"...

Look at it this way, backpressure is pushing back against the piston that's trying to push the exhaust gases out - the greater the back-pressure, the more force that is required, and that force comes from the crankshaft and isn't available to actually produce power/torque.

With production engines, there are many compromises in the exhaust and the exhaust tuning, and backpressure can reduce the differences over the rpm range.

There are a couple of problems, often seen with modified engines, and that's when a "tuned" length exhaust is incompatable with the actual needs of the engine's breathing and/or the fuelling and timing isn't changed to match the changes in the engine's breathing.

It makes sense to me that little to no back pressure makes more power but I was curious because my dad talked to a guy about his exhaust and getting a tune for his Yamaha Eluder motorcycle (1900cc V twin). The guy said the stock pipes with little modification is better than straight pipe or the zombie pipes (aftermarket mufflers) and you’ll get best performance out of the stock with a hole drilled in a plate inside the muffler. And I’ve heard others say that you need some sort of back pressure and you’ll get better performance but it never made sense to me.

It's all about exhaust gases evacuating combustion chamber and geometry of pipes. If pipe diameter (starting from valve seat) is too small - it hurts the flow and you get back pressure. If pipe diameter (again, starting from valve seat) is too big - same thing, you loose velocity and get back pressure. Same with pipe geometry - every single little turn slows flow down and adds up to overall back pressure so it's always a compromise between exhaust gases velocity and particular exhaust system configuration that dictates the amount of back pressure present. At the same time, as Gord said, if proper pipe size is chosen it can increase flow velocity and reduce the back pressure by evacuating exhaust gases faster...