No Cats. Robes H.P.?

[kuwait]

well i cutted my 6 cats away , and i can tell you that i got like no LOW END AT ALL , the car just floats around like a boat and dosent come alive until 3k and higher so basicly , i dont race from a dig anymore .....
i had to go buy a new h-pipe to solve the problem.....but hell i admit it at higher rpm you will pickup up to 5-9 good ponies

 

[Mustangl3]

before i put my o/r h pipe and diablo predator in i was running consistent 13.9s with a best of 13.8. Now im running consistent 13.6s@ 104. I know most of my gains came from the h-pipe.

 

[csledd]

well i cutted my 6 cats away , and i can tell you that i got like no LOW END AT ALL , the car just floats around like a boat and dosent come alive until 3k and higher so basicly , i dont race from a dig anymore .....
i had to go buy a new h-pipe to solve the problem.....but hell i admit it at higher rpm you will pickup up to 5-9 good ponies

get some 4.10 gears and you'll be good to go from a dig

 

[MadonnaRioRedGT]

hognutz came the closest to getting the idea of why horsepower/torque can be gained/lost at high/low RPM from performance/stock exhaust systems.

As well, the "backpressure" idea is not true at all. A lot of people will equate low RPM torque with needed backpressure - this however is not true.

The key to understanding this whole concept is EXHAUST GAS VELOCITY. Trust me, I wrote an entire paper on this, sort of like a "myth buster" idea.

This is from an engineer's stand point as well.

- Brian

 

[propellerhead]

hognutz came the closest to getting the idea of why horsepower/torque can be gained/lost at high/low RPM from performance/stock exhaust systems.

As well, the "backpressure" idea is not true at all. A lot of people will equate low RPM torque with needed backpressure - this however is not true.

The key to understanding this whole concept is EXHAUST GAS VELOCITY. Trust me, I wrote an entire paper on this, sort of like a "myth buster" idea.

This is from an engineer's stand point as well.

- Brian

I've read an article on that when I was reading about valve timing and cams. It might have been yours. You should post a link to it.

Reader's Digest version: The intake valves start opening as the exhaust valves close. With both valves open the movement of the air helps clear out the chamber of exhaust air and bring in fresh air/fuel. Larger exhaust pipes means slower velocity. You can get more air out but at a slower speed. The timing of the valves and the velocity of the exhaust is not in synch anymore. At low RPMs, the lowered exhaust velocity is costing you some power. This is seen as a loss at the low end. At high RPMs, the exhaust velocity is high enough to take advantage of the larger pipes. This is seen as a gain at the high end. Hence, it's not really caused by a loss in back pressure. It's due to a lower exhaust velocity at low RPMs.

 

[Mustangl3]

but how can the exhaust move slower with 4 less cats?