NickSezz

I always wondered why people talk about back pressure so much here... It is usully used as a term when talkin about 2-stroke engines. They don't have valves to control fuel and exhaust flowandrely onpressure waves from a tuned (shape tuned) exhaust pipe.

These pressure waves come out of the exhaust port, run through the header, and through a usally weird shaped tuned pipe that is designed to change the pressure waves' shape and speed. By doing so, the waves bounce back through the exhaust system and force more air and fuel into the engine through the exhaust portcreating a super charging effect. Remember, 2 stroke engines are not as efficient as 4 strokes are because they release exhaust gas during the same stroke as the new air and fuel enters the combustion chamber. During this time, some of the new air and fuel is wasted and lost out of the exhaust port of the engine. Without a tuned pipe, this can only be controlled by thelocation and offset of the ports in the crake case in realtion the the timing and travel of the piston. By adding the tuned pipe that creates a controlled back pressure wave, it forces that unburnt air and fuel back into the engine at the right time to create a larger explosion.

From my work with Nirto Rc cars, in general, a longer or fatter header pipe inceased low end power and torque, while ashorter or skinnier header made top end better. The tuned pipes are simple shaped for these small engines andare usually cone shapped, long and fat, or long a skinny. The cone shaped pipe created the best all round power by starting skinny and ending fat. The fat pipe creates more torque, and the skinny pipe was good for top end. For example: If you wanted good low end as well as pretty good top end, you could add a larger fatter header with a long skinny pipe. In general--More back pressure, more top end. Less back pressure, more low end. All of these principles apply to other 2 stroke engines like the goped I used to have and dirt bikes, but they are a little more complicated.

Now taking in terms of a 4 stroke. Since there are valves that contol the intake and exhaust flow, a special pipe in not needed for help. As I always heard, you want to get the exhaust gas out of the engine as fast as possible so new air and fuel can enter. This calls for a simple and large opening for the gas to escape. Done. Easy. I say the best exhaust system is no exhaust system.

Do you see top fuel dragsters with complicated exhausts? NO. They have large headers that point up. They burn Nirto Methane, and let me tell you, that Sh*t burns the hell out of your nose if you breath in theexhaust fumes. The headers direct that gas away from the car, as well as create down force on the car. Yes thats right down force! So much air is coming out of those pipes that when pointed up, it pushes the car down. If you ever saw a race where a few cylinders go out on a car, it starts to move around on the track more.

Now applying this to a modern mustang. Our cars sadly have computers now. This means that the chages we are aware of, the computer might not be. Changing the exhaust on the car will change the readings the O2 sensors are getting as well as some other things I probably don't know about. This is what causes a gain, or maybe a loss in performance as well as the exhaust letting air out faster. Blame the computer, not your exhaust system! I think that is whats being confused with back pressure, a simple 10101010101 error.

All I have said may not bee 100% accurate or complete, I am just throwing out what I know to help you guys. If someone has a correction for me I would be happy to accept as I am still learning and always love to learn more. Later --Nick

billyjo

before my GT i had an 05 v6 and i had flow master dual exhaust put on and it uped the HP and added about 2 miles per gallon so the back pressure crap is wrong. So if you can do it, i did and i loved it. Though if i had a choose again at that time i would not picked flowmaster. So do your homework and pick the exhuast that you like.

raubt

Why is that (no to Flowmaster), if you don't mind my getting off topic?

billyjo

they needed to be replaced twice due to the inner parts coming lose and rattling. Also there drone was terrible inside the cab. So that is why

The Ghost

I agree with "most" all above about not needing backpresure. But one part of the mix has been left out. And it sort of mirrors what was said earlier about two strokes. If you go changing around your exhaust with something not actually designed for your car, say a GT stock set up on a V6. there is a pretty big potential for some power loss. But backpresure or lack of isn't why. Like said above it has to do with the pulses coming out of your engine. If you ever look at a set of headers you will notice there is almost always one tube that just doesn't look like they bent it right. Well it is right, they do that to get the exhaust pulses timed so that they stack properly leaving the collector and stay that way down your pipe. If you are not running headers there are a few tricks to keep the flow as smooth as possible like putting a X-over or H-pipe in the spot in the pipe where it is known that these pulses are not stacked right. If you could put a ping pong ball inside an H-pipe and be able to see it, you'll see it going back and forth rapidly, not just sitting there. It's because the placement of the pipe is so that when there is a pulse on one side it is between pulses on the other side. From this point back in the exhaust everything is pretty nuetral. Changing pipe diameter or useing parts not made for your engine will change how this works. Used to be we would play around with tailpipe length to try to "tune" the pipes so we had the best flow we could get for racing, but we neverran H-pipes back then.If you are considering changing out your car to dual, or adding an X-pipe, or whatever. Use parts that are made for your specific vehicle from reputable companies. They put in the R&D to get things tuned right. Don't be afraid to call and talk to factory reps about your plans. They can offer you exactly the right combination of parts.

mustangman02232

backpreasure is bad in any way shape or form, it makes preasure in the exhaust making exhaust gases harder to escape, However your exhaust needs a certain velocity to make the exhaustgasses come out of the pipe.try running a mile breathing through a straw. then try using something like a 2" hollowed out tupperware cup, then a 6" drain pipe, while you can breath easier, the old air just sits there and you have to force it out harder

danomano

Here is an unbais report of backpressure


http://auto.howstuffworks.com/question172.htm

mustangman02232

not only is it the hardest bolt on, it doesnt do squat unless they are long tubes

Sherwood06GT

Yea, I just connected 1/4" copper tubing to my Headers and ran it all the way back. AWESOME back pressure!!!

Seriously, with a S/C it is much better to really open it up. Hence, my LT Headers.

Norse1974

Yeah man you dont need any back pressure!LOL!Im about to install my MAC 1 3/4 L/Ts & Mac Prochamber & Mac axel backs!Can't wait to hear what she will sound like!