Catalytic Converter and Horse Power. Why more HP? Part 2

Back to reduced back pressure
(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.

Note: The

Catalytic Converter and Horse Power. Why more HP? Part 1

When I replaced my catalytic converter it had to be cut out. The new one has to be welded back in. Facing all that work, I didn't even consider cleaning it as seen on Ericthecarguy's channel in this video catalytic converter cleaning. I've seen a lot of Honda's on Ericthecarguy's show and one Honda on an AutoZone show easier to remove catalytic converters with flanges. Theoretically, You can just bolt the new one one. Catalytic converters last too long and exhaust rusts, so "easy" is not how it usually still turns out. How kind of Honda to help make this possible. (Forgive me if I forget that maybe Eric had to add the bolt in flange to make that true?)

Anyway. I bought my catalytic converter (often called a cat) from Auto Parts Warehouse. First and only product I've bought from them, being fans of AutoZone and O'Reilly. I got it for $98. The reason I bought it here was because when I talked to O'Reilly's or AutoZone they wouldn't look at their database without my car in it. So, all they would see is stock cats. Only Auto Parts Warehouse out of 5 stores would work with me to look at cats by their diameter of pipe. I bought an Eastern Cat made for GM cars, which were designed to resist coolant and oil better than other cats since these leaks burned up so many cats on GM cars. It was legal in all but CA and I think NY. Catalytic converters don't have to always be expensive. If you live in CA or NY this article really doesn't apply to you (be sure to check your local laws). Since I thought I had a 2.5" catback upgrade I went with a 2.5" catalytic converter. I wanted a little more power. I went from 59 to 90.1 wHP. Not a little more!

It turns that my catback upgrade of 2.25" exhaust measures 2.5" on the outside, whoops. So, that was also a lot of extra work, but I wouldn't have done it any other way as this reduced back pressure further. Since catalytic converters are the biggest bottleneck on the exhaust getting out of the tailpipe, I figured bigger was better. I had to use pipe conversions from the catalytic converter to the down stream pipe. Plus, the 2.5" OD catalytic converter needed a 2.5" pipe into it, before the pipe converter would work. The converter and the catalytic converter were both 2.5" OD, meaning it fit over 2.5" and was more like 2.75". ID means it'd fit in rather than over. If ID and OD aren't mentioned it SHOULD be actual 2.5", not the case for the catalytic converter.

The worst part of the conversion was going from the 2.5" OD pipe of the catalytic converter to the 1.75" stock down pipe. They don't make a conversion pipe do that all at once. Took 2 conversion pipes and hours of cold steel work with a pipe expander that broke on a 2" pipe to get big enough to fit over rather than under the 1.75" down pipe. (The pipes I bought were 1/8" thick which adds to 1/4" of size for how it fits, but the stock pipe's were much thicker, maybe .375" thick.)

Back to back pressure on part 2 of Catalytic Converters and Horse Power.

by AutoBravado

Discussing Tire Pressure or PSI

In my 2004 Nissan Frontier I run 40 PSI and I can't remember what they recommend, but it's definitely less. I ran 44 PSI for a few months and I noticed that I was stiff enough that I was wearing my tires faster and dropped back down to 40 and I was happy with what happened after another few months where I barely noticed wear.

When I have a big load I go up to 50 PSI. My tires are rated at 55 PSI, but this is based on the logic that a heavier load means the contact pad on the bottom of the tire was bigger. I didn't want a blow out. I followed the advice of a local grandpa who's tried everything when it comes to tire pressure changes and looking at my tires and feeling how they were cooler with more PSI when the truck had a heavy load all matched up with what he said.

On my 1999 Chevrolet Prizm they recommend, if memory serves 32 psi. I ran 40 to 44 for a long time following the same grandpa's advice (not my grandpa, just saying he's played with this for a long time). I put up with this for a few sets of tires wearing out at 1/2 what the tire manufacturer recommended. I decided to try 36 psi and my tires still wore just as fast. I went to 32 psi and finally my tires were lasting a lot longer. They only look half worn and I've driven as far wearing out the other tires. (same brand)

You see the problem on my 1999 Chevrolet Prizm is that it has no cam adjustment. So running my tires softer like the manufacturer recommends under my circumstance is preventing the inside of the tire wearing.

Recently I posted this opinion about how tire pressure effects a car's miles per gallon (edited):

Air pressure? Just do what the manufacturer recommends and you'll have better mileage and long tire life. That's putting it simple. Let's go complicated. Putting extra air in stiffens up your tires, reduces rubber movement in the tires and you'd think it's raise your mpg. What actually happens: your tire real height (after the weight flattens the bottom of your tire) goes up and your car will go "fewer miles". You see the taller your tires the farther you actually go, but your miles goes up slower from the car's perspective or on the odometer. This will appear to reduce your gas mileage. I ran the math on my mpg going up and down with this experiment. It was equal to how many apparent miles I was driving from taller and shorter tires.

Long story short apparent mpg changes from these up to an inch changes in tire radius didn't change my actual real mpg at all. It just appeared to be changing.

I used to run my tires with higher psi - and chose tires that could handle it. All I got was tires that wore faster because they were more sensitive to alignment never being perfect no matter how much you get alignments and a lower apparent mpg...the worse consequence is that over-filled tires increases stopping distance and if you accelerate quickly you have less traction. Just keep it simple and do what the manufacturer recommends unless you have custom wheels - you'll have to rethink it at that point.

Back to something new:

When I tried the putting more or less air in a car it was on a 7,000+ mile car trip. I was in a 1996 Saab 900 SE. I ran the math on how far the Saab was going according to it's odometer. I ran a ratio off of that and how tall my tires were at a "recommended" tire pressure versus stiffer pressures I was into at the time. So as I changed the tire height I knew that the actual circumference of the tire was changing. I ran the circumferential changes as a ratio against how far the car was going more or less distance against the car miles per gallon. Equal to how much better my car appeared to be doing on it's miles per gallon was the ratio of how less much less distance the car went due to the tires being shorter. Exactly equal. So I believe that, at least based on this one experiment, it's a myth on how much your tire pressure really effects mileage. I even messed the car up for one of the drive tires having more or less PSI by 6 PSI than the other and it still wouldn't effect the car's miles per gallon (of course when you include the ratio of how much farther or shorter the car is ACTUALLY travelling).

Note: When I say exactly equal I should say that the amount of change was 4-6 decimal places in or using 6-8 significant digits since the mpg was in double digits like 36 miles per gallon. That car has active readouts so I didn't have to fill up at every PSI change to get the numerical changes. I ran these experiments for about 1/2 the trip. The ratio of change kept being consistent up hill, down hill, across relatively flat terrain and over mountains.

by AutoBravado