now ive heard alot of different opinions on this one but is back pressure a good thing or a bad thing being at the fact that i have a naturally aspirated
car. give me your thoughts boys.
thanks

 

Backpressure is always bad. The focus should be on exhaust stream velocity. When the exhaust tubing is TOO big it will LOSE heat and the gas will slow down. You want the quickest path out while keeping an operational amount of heat in the pipe. For us N/A guys this = 2.25-2.5 inch piping.

 

I would like to note that this in not just my opinion, this is fact.

 

Agreed back pressure is bad, however if your piping is to big you will lose velocity and the gases will not escape in a timely manner thus losing hp. I have heard that having more back pressure (to an extent) will actually increase torque. When i had my cat back replaced, i had to drive around with the exhaust exiting out of the cat. I noticed alot of low end power lose when this was going on (and VERY loud to boot), and when i got my megan cat back put on, the power returned.

 

"Engines need some back pressure to work properly. A small amount of back pressure helps the engine expel the exhaust in a uniform fashion. A good analogy someone gave me uses a drinking straw as an example. Drinking through a coffee stirrer represents a restrictive exhaust with a lot of back pressure. It is difficult to drink through a coffee stirrer, as it is difficult for an engine to expel exhaust through a restrictive system. A normal drinking straw represents a good free-flowing exhaust. It is easy to drink through a regular sized straw, as it is easy for an engine to expel exhaust through a good exhaust system. However, if the straw is made too big, it becomes more difficult to drink through it. This represents a lack of back pressure."

http://everything2.com/index.pl?node=Back%20pressure

 

MagnaFlow's Frequently Asked Questions
Question: Why ISN'T a bigger pipe always better?

Answer: Don't be fooled! Bigger is not better! Many people think that having the biggest diameter pipe is the best way to make power.
Not true. Due to a variety of factors, extensive testing is required. We've dyno'd extensively and our systems yield optimum power increases. Some manufacturers claim even higher horsepower numbers.

It is a fine line to reduce backpressure while maintaining good exhaust velocity. It is not about getting the biggest pipe, it is about getting a more efficient pipe diameter while maintaining exhaust velocity.

There has to be a balanced design to enhance the maximum engine output, exhaust gas velocity, and sound. For example, imagine blowing air through a straw (comparing it to a smaller diameter pipe). This would take time to release all the air from your mouth, and you would feel pressure in your mouth while doing so. Now imagine blowing air through a paper towel roll (comparing it to a larger diameter pipe). You will relieve all your air much faster and feel little or no air pressure in your mouth because of the larger capacity of the tube. This is why it is important to get the correct size piping in order to relieve backpressure while maintaining thermal efficiency.


http://www.magnaflow.com/07techtips/faq/question10.asp

 

freeway, you're bomb dude, thanks.

 

haha good analogy man thanks

 

Why don't you check the stickys for the 4th gen forum. mzmtg covers the subject well.