Originally Posted by DeathMetalTruck

If you search around you can find specs on the correct size of piping for how much horsepower your engine puts out. I do agree that if your pipe sizing is much too big you will end up losing exhaust velocity and lose power, but I have never believed that you need cats or mufflers for backpressure. All they do is reduce sound and clean air...nothing more.

Exactly...why would every race car or off road vehicle run wide open headers or no cats....cause there is no restriction and more power from that, but you still need correct pipe sizing.

Originally Posted by Faster150

back pressure is a myth. the greater the exhaust velocity the better. cats restrict exhaust flow thus lowering the exhaust velocity. thus lowering power. u never see NHRA cats or NASCAR or baja trucks with cats do you?

Originally Posted by MGD'S First Link

Remember that backpressure does NOT equal torque, as so many claim, including muffler shops, even some exhaust system manufacturers & "experts" often claim this. Backpressure contributes to reversion during overlap (of course this depends on platform & cam specs, too), but more backpressure does NOT automatically increase torque. Now, you just *might* happen to make more torque with more backpressure in a given situation, but not because of the backpressure, that is just coincidental; more torque was amde because the resultant *velocity* was higher without being overly restrictive, that's all.

*Velocity* yields torque, so keeping the exhaust flow *velocity* as high as possible without excessive backpressure is the key to getting power gains throughout the entire rpm range. In these heavy trucks & SUV's, the torque below 3000 rpm at *any* throttle position is far more critical to driveability and overall performance both on the street and at the track than big pipes flowing big numbers & yielding power gains only above 2800-3000 rpm. That being said, you can indeed "have it all," with a properly flow-engineered system.

The factory 2.5" single system in the 1997 & up F-150 is actually designed to provide maximum torque on part-throttle below 3000 rpm, specifically, and it does this very well indeed, at the cost of both horsepower and torque at heavy throttle, and at almost any throttle position beyond about 3000 rpm. And this is, in very general terms, why the vast majority of aftermarket cat-back systems or exhaust mods cause hp gains at higher rpm, but kill torque below 3000 rpm at virtually any throttle position. How does this happen? When the flow is opened up without proper flow engienering to maintain spent exhaust gas velocity, you lose the scavenging effect that helps to pull spent exhaust gases from the cylinder head, and *that* is the specific mechanism that causes the classic loss of torque so many people complain here about after exhaust mods.

Originally Posted by 02XLT4X4

Sounds like the same thing to me.

Originally Posted by 02XLT4X4

Sorry, your agreeing with not listening to anything Faster150 says led me to believe you didn't agree with him.

I agree about leaving the cats, aside from the minimal effect they have on performance, the MIL Eliminators you have to run don't give you computer the true story about how your truck is running.

Originally Posted by chester8420

Jbrew, I don't have time to read and research, so just tell me, What size pipes are you running after your headers? Duals or single? If duals, how far from the header collector have you placed your x-pipe? What kind of muffler? No cats, or high flows? Where do the pipes exit? What kind of tip?

Originally Posted by jbrew

BTW - Theres no law in Michigan saying you have to run cats. No emission testing here..

Originally Posted by 02XLT4X4

Sorry, your agreeing with not listening to anything Faster150 says led me to believe you didn't agree with him.

I agree about leaving the cats, aside from the minimal effect they have on performance, the MIL Eliminators you have to run don't give you computer the true story about how your truck is running.

Originally Posted by jbrew

Thats another reason right there why I'm not running those. Plus - I purchased 4 new O2's for the system.