---Backpressure in exhaust; good for city bad for highway!---

[basslover911]

What i have been thinking;

Backpressure is good because it increases torque, so that is good for city driving where you need to constantly accelerate and decelerate.

But what about for constant cruising? When you dont need that torque... Wouldn't less backpressure be the best since air would flow out much better?

[Duffman]

Backpressure isn’t good for anything except when used for sound attenuation.

[markweatherill]

On a production car, 'back pressure' in the exhaust is factored into the cam timing. The exhaust valves can begin to open earlier than if an open exhaust was used, a benefit at lower engine speeds (i.e. in everyday driving).

[Ryland]

It's not about back pressure, it's momentum! the exhaust is exiting in pulses not a constant flow, if it was a steady flow then larger would be better, but your engine is not a turbine... and even with a turbine you have to tune your exhaust to keep the momentum to help the engine run better (at least the books on turbine design seem to say so), so what it boils down to is if you believe in physics a properly sized exhaust is going to treat you best, if you are 16 and were given a car, and failed math class then go with a larger exhaust.

[eco_generator]

Originally Posted by basslover911

Backpressure is good because it increases torque

You have some more reading to do...

[aerohead]

Here are a couple of ads for leading high performance mufflers


Both have engineered backpressure into their products for low speed economy,then provided short-circuiting for high speed efficiency
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Here,YAMAHA (read Ford SVO engine builder) designs it's 'smart' exhaust,with computer-controlled valving to maintain optimum backpressure under all load conditions

[ksa8907]

The statements that "back pressure is good" or "an open exhaust is best" are nonsense. To break any theory you take it to the extreme. So if i run 1/2" exhaust pipe i should see an increase in efficiency? How about i just remove the exhaust entirely including the manifolds, will that increase power?

Its been said already, but a PROPERLY SIZED exhaust is what is important. Pressure is only used to suppress noise, notice how many new cars at idle have a, for lack of a better term, throaty exhaust at idle then gets quiet as they accelerate?

[oil pan 4]

On a diesel exhaust back pressure is not helping anything.

[Frank Lee]

Originally Posted by ksa8907

The statements that "back pressure is good" or "an open exhaust is best" are nonsense. To break any theory you take it to the extreme. So if i run 1/2" exhaust pipe i should see an increase in efficiency? How about i just remove the exhaust entirely including the manifolds, will that increase power?

This isn't about extremes, and there is a case for throttled exhaust in engine management.

[Baltothewolf]

My insight is straight piped from the head to the tailpipe (with the exception of the resonator, was way to loud without it). I didn't really notice a difference except at high rpm situations (above 3500rpm). It seems more peppy than it did before. But who knows.