[billabongsmp]

is it bad to unbolt my exhaust after the mid pipe.. i di it and it was loud as f#ck!!!! abd do you lose power or torque???

[WildWill]

yes the mufflers provide the backpressure necessary to give you efficient torque and horsepower. you should definitely feel a drop in low end torque when you do that - especially if you have a close to stock motor.

[rru95GT]

Destroying a myth.

Some say that "an engine needs backpressure to work correctly." Is this true?

No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.

The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.

The other reason why people say "backpressure is good" is because they hear that cars that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure.

The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.

Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.

Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Earlier cars with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel (caused by the camshaft overlap). While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.

Modern Fords don't have to worry about the effects described above, because the computer that controls the engine will detect that the engine is burning leaner than before, and will adjust fuel injection to compensate. So, in effect, reducing backpressure really does two good things: The engine can use work otherwise spent pushing exhaust gas out the tailpipe to propel the car forward, and the engine breathes better. Of course, the computer's ability to adjust fuel injection is limited by the physical parameters of the injection system (such as injector maximum flow rate and fuel system pressure), but with exhaust backpressure reduction, these limits won't be reached.

Adopted from The truth about exhaust backpressure and torque

[billabongsmp]

so your saying its good? oh and you know if you have cut out valves it pretty much do the same thing.. so wats wrong with it lol??? i think it sounds badass

[95cobra50]

and you're also saying that going from a 1.5 inch exhaust to a completely smashed 1.5" exhaust to 2.5" exhaust on a 1970 buick lesabre could do damage to the engine?

[billabongsmp]

some fucking civic bapped my shit last night and took off!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! WTF!!

[WildWill]

what does "bapped my shit" mean??? I must be getting old or something.


rru95gt... that's an interesting write up. thanks for the info. but I would like to see actual numbered results to prove a simple test of whether taking the mufflers off or leaving mufflers on is better for perfomance.

to the OP - maybe what you should do is get yourself to a track, leave your mufflers on for a run, then unbolt them and run again and see if there's a difference.

[billabongsmp]

bapped= like umm got hit..... this honda clipped my passenger front bumper it was a hit n run.. i wouldve chased him but i had to pull my fender out from the wheel well

[95cobra50]

i must be getting old, too... i'd never heard of bapped, either. hopefully you at least reported it to the police?

[WildWill]

Originally Posted by billabongsmp bapped= like umm got hit..... this honda clipped my passenger front bumper it was a hit n run.. i wouldve chased him but i had to pull my fender out from the wheel well

gotcha... so wait... you SAW the guy hit your car and drive away????

I hope you at least got a plate number man...

[lowp51]

Never heard "Bapped" either, Must be getting old as well. I would have been pissed!!! hope you got the guys plate.

[sickfox]

its official im getting old too i dont know "bapped" either hell my spell check didnt know either haha must be time to upgrade!~

[billabongsmp]

no you guys arnt!! its just wat some ppl say around where i live.... bay area california

[WildWill]

oh... he's a Cali kid. Ok nevermind all that we just said. Who knows what you guys say down there... lol

[ryanhewett466]

"bapped my shit" hahaahaha