exhaust and back pressure

[92rangnick]

i cut muffler off the brandnew exhaust kit that came with truck when i bought it cuz it was way to quiet, i have both cats on to 2 1/2 pipe that runs over wheel and comes back to where it wud be regular stock exhaust, u think this is enought back pressure

 

[alwaysFlOoReD]

Why is back pressure needed?

Richard

 

[jhammel85]

I've heard that it matters and I've heard it doesn't.

I'm not sure I really understand your post though. Did you take the muffler off or is it just cut off behind or after the rear axle?

 

[92rangnick]

i cut out muffler then subbed a piece pf pipe where muffler was so its not straight all the way back it still has the hump over axle

 

[Dirmaid]

The reason that some people say you need back pressureis mainly because they've always heard you need back pressure. The people that say you don't need it believe in efficiency of air flow.

The theory mainly behind the need of back pressure (correct me if I'm wrong. An old senile mechanic told me this) is on the older cars the air and the fuel wouldn't mix all of the way in the cylinder, so the surging back pressure on the other side of the exhaust valve would form a sort of "swirling" effect inside of the cylinder to properly mix the gas and the air. With newer engines, there are systems that usually will compensate if there is unburnt fuel in the system (which would be a problem with no back pressure on older engines).

Another misconception is people confusing back pressure and proper air flow. In a bigger pipe, air flows slower than the same volume of air in a smaller pipe. This velocity is needed for the bernoulli's principle (suction is made when air is pulled over an open hole) to be applied at the exhaust valves to pull exhaust out and intake in during overlap of the valves. Bigger pipes= slower flow= less suction due to good ole bernoulli

So to answer your question directly, you'll be fine, just might sound like a weed eater with a 2.9

 

[92rangnick]

ten four, idk no weed eater sound out of my 2.9. with intake it sounds better then any 4.0 i know with custom exhaust

 

[kemo]

backpressure is something that you need on a 2 cycle.