Loop headers ?

[wbilotta]

How do they affect the power band on a Briggs engine and why ?

Just curious.....

 

[frederic]

Loop headers are designed to aim the exhaust away from the rear tires and your head, and claim to increase top RPM performance because they have a slightly narrowing cone off the exhaust port. The claim is they increase the velocity of the exhaust gas to allow for increased chamber scavaging. This matters with racing engines that are designed with this type of knowledge being taken into consideration, but for the average lawnmower engine it's a moot point as there are other issues far more serious to be taken care of than a cute curvy exhaust pipe.

Narrow tubing decreases the flow inside the pipe more than one might think. Aside from being narrower, one also has to contend with the "boundary layer", which is a thin "film" of air, gas or liquid that clings to the inside wall of the tubing and resists "sheering", and moves much less than the air, gas or liquid flowing in the center of the tubing.

The best exhaust is a straight exhaust - every bend slows down the movement of the air because it "bunches" on the outside of the bend, much the way you, your friends, and your McDonald's extra large sodas will if you decide to take an exit ramp at 80 MPH - you all get "flung" to the outside of the curve inside the vehicle. Exhaust does the same thing in the pipes where it bends.

 

[wbilotta]

Loop headers are designed to aim the exhaust away from the rear tires and your head, and claim to increase top RPM performance because they have a slightly narrowing cone off the exhaust port. The claim is they increase the velocity of the exhaust gas to allow for increased chamber scavaging. This matters with racing engines that are designed with this type of knowledge being taken into consideration, but for the average lawnmower engine it's a moot point as there are other issues far more serious to be taken care of than a cute curvy exhaust pipe.

Narrow tubing decreases the flow inside the pipe more than one might think. Aside from being narrower, one also has to contend with the "boundary layer", which is a thin "film" of air, gas or liquid that clings to the inside wall of the tubing and resists "sheering", and moves much less than the air, gas or liquid flowing in the center of the tubing.

The best exhaust is a straight exhaust - every bend slows down the movement of the air because it "bunches" on the outside of the bend, much the way you, your friends, and your McDonald's extra large sodas will if you decide to take an exit ramp at 80 MPH - you all get "flung" to the outside of the curve inside the vehicle. Exhaust does the same thing in the pipes where it bends.

Understandable. So if a straight pipe is best, what length is ideal ? I would think a longer pipe would increase the amount of resistance flow.

 

[freakboy]

u want it longer then 12 inches. anyshorter the rush of cold air when the engine shuts off will make the valves more brittle.