Test with stock, hiflow, and no cats on the K&N dyno.

Synopsis

Breathing through an aftermarket intake, header and cat-back exhaust system, our Civic mule put down a respectable 147hp and 105 lb-ft to the front wheels on K&N Engineering's dyno. Not too shabby, considering the car was still huffing through the stock OEM catalytic converter. Eager to see what we could gain by uncorking the exhaust, we bolted on the first aftermarket cats.

After removing the OEM cat, we welded and bolted up an OBD II Magnaflow ceramic-core catalytic converter in place of the stock one. With the Magnaflow cat installed, the Honda turned the rollers to the tune of 150hp and 107 lb-ft to the wheels. The ceramic-core cat netted us an additional 3hp and 2 lb-ft to the front wheels. Obviously, this cat really can flow more than stock.

Next up was the metallic core Magnaflow OBD II cat. Because metallic cats can take more abuse and richer AFRs (and generally flow more), these are often the choice of the performance-minded tuner. After much cursing and a bit of charred flesh, we put the fancy metallic-core cat onto the Civic. Apparently, the metallic core unit does indeed flow slightly better than the ceramic unit. But when we say slight, we mean slight. The metallic core cat netted us a 4hp gain to 151hp and and 107 lb-ft to the wheels. So, unless you are running a rich AFR (like in a boosted application) the extra cost of the metallic core might not be worth it. However, if you are running a rich mixture, the metallic cat is still your best bet.

With the testing of all three cats out of the way, it was time to unplug the exhaust and let her rip without that pesky brick in the exhaust. No matter how you cut it, a cat is a restriction and costs power, right? With the moment of truth at hand, we bolted in our test pipe - eliminating the cat entirely. On our final pull we stood eagerly by the dyno's monitor, waiting to see the results. Wait ... here it comes ... 152hp and 108 lb-ft - a gain of one measly horsepower and one lb-ft of torque at the cost of breaking the law.

Note: Article has additional info on Ceramic vs Metallic and ODB I vs ODB II cats.

 

So technically your total gain is 5whp and 3tq with a test pipe and breaking the law? nice

I say its worth it till inspection time rolls around or move to a state that doesnt have annual inspections like mine

 

I know this test was done on a car instead of a truck but why do people on here talk about it's not good to lose alot of backpressure but the testers talked like the less backpressure you have the more power you'll gain? Which was proven to be slightly true in this dyno test!

 

With a 5500lb pick up truck, you need the backpressure & low end torque to move without getting 8mpg.

 

Ok So the more backpressure you have the more low end torque and the less backpressure you have will cause the peak torque to move higher up in the rpm's?

 

No.
Backpressure is ALWAYS bad. The problem is that you need to keep the exhaust velocity up at lower RPM in order to produce decent power there. That requires a smaller exhaust which gives more backpressure, hence the backpressure = torque myth. To further complicate things, exhaust velocity is a function of diameter^2 and backpressure is a function of diameter^4 so small changes in diameter can have a huge affect on backpressure.