(Click here for Catalytic Converter and Horse Power part 1)
For a while, I thought less back pressure was the key to my additional power. I think there are a couple more factor's. My 1999 Chevrolet Prizm, same as the 1999-2002 Toyota Corolla, or 8th generation Corolla, has an ECU that may just be determined to not be a polluter. A bigger Catalytic converter decreased my emissions tremendously, still 400 cell by the way, I didn't go for high flow (often only 100 to 200 cells and in many cars that guarantees P0420, catalytic efficiency is too low for emissions requirements). If the car can run richer at WOT (wide open throttle) then maybe it'll just go ahead and burn richer if it still will keep the environment clean. So, that's my second theory for why so much extra HP. Note: this car is more famous for having a too sensitive ECU for that second O2 sensor, so I would not recommend a high flow catalytic converter. If all my theories in this article are true, you may not get more power. And if you do, it'll probably only be at high RPM's and if you're like most of us with an automatic, you'll only see start to see that power above legal speed on the freeway. Reducing back pressure reduces low to mid range torque, which my engine is doing most of the time.
My 1999 Chevrolet Prizm actually has the 2000 engine upgrade the the VVT-I, and an upgraded wiring harness and ECU to match. WHP on these cars tends to be about 109 (versus factory reported 125 at the flywheel). That's what I'm getting now. Since the catalytic converter I've completed replaced the shocks and struts in the back. Since I'm not using a dyno, lost acceleration on the road will lower my HP numbers. The "real" HP that everyone wants from a dyno, may be more accurate, but it can't account for a bad suspension (or as much). In fact, I think a dyno compensates for a bad suspension.
Back to catalytic converters and a 3rd factor for the "extra" or restored HP?
My old catalytic converter didn't appear to have any function. Watching on a live scanner the front and rear O2 sensors reported nearly identical electric values. Sometimes I could spot that the rear O2 sensor would say what the first one said on a slightly delayed basis. I could easily see sunshine through the converter so it wasn't terribly clogged or melted, but I think the wholes were corroded enough to look smaller. (See my new Upstream O2 sensor article about diagnostics and understanding.)
Both the stock catalytic converter and the new one I bought reported 400 cells, and since I had a bigger one that my have accounted for the additional appearance of space.
My next exhaust upgrade will be a 4-2-1 tuned exhaust. A 4-1 will help more in the higher RPM's while a 4-2-1 will get more power in the lower to mid RPM range, which is good seeing as how most of the HP numbers reported happened when the car was between 3,000 and 4,400 RPM's. The car likes to shift too soon around 3,300 even at WOT so until about 80 MPH at WOT, you won't get the 5,500 RPM's needed to see the 109 HP.
Weapon Dragon R short ram intake had me up to 41 miles per gallon. This had me back down to 28-31, which is still better than stock. With a lot of practice on how I drove using the Torque App, I got back to 41 miles per gallon, and even when I spend time doing these HP tests, I don't manage to get lower than 41 miles per gallon most of the time. Occasionally, I get 38 miles per gallon during a performance test. That's simply incredible. Used to be that if I sped up quickly a lot less in a gas tank I'd be losing 3-6 miles per gallon, and that's over the whole life the of the gas tank. I still got 41 miles per gallon over the whole gas tank during these tests, just sometimes I got 38 during the test.by AutoBravado
Try my other catalytic converter by Eastern article.
Try my video on YouTube. My video shows the catalytic converter in action so you can get a practical example of live sensor data.
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