JoeT
01-18-2004, 12:30 AM
In the quest for power, acceleration, speed, after the cat back exhaust, the next step usually is to look for a set of headers to help augment the flow of gasses and make it easier for the engine to breathe. Besides, what's an engine anyway but a large air pump. The easier for it to inhale and exhale, the freeier it is to rev until it's not allowed to.
4 Stroke-Cycle engines are all basically the same, Intake->Compression->Combustion->Exhaust are the 4 strokes per cycle that occurs at every 720 degree revolution.
Getting back to the Quest for Power. Once again my goal was to increast the available torque and power available for my hobby / sport of Autocross. Which means I need power under the curve to stretch as far as possible, and start as low as possible. I've already installed my 2.25" cat back exhaust, now I need to get rid of my restrictive stock exhaust manifold and stock catalytic converters.
Again, I did research, lots of it to look for the absolutely the best headers for my application. Keep in mind, the 2.5L Boxer engine from our scoobs have a redline of 6250 or 6500 depending on SOHC or DOHC. My car was a SOHC variation with a slightly lower redline, which means at this low rpm range and a volume of 625cc / exhaust pulse (add temperature), I needed a header with fairly long primaries to do "scavengine" within the primaries, relying primarily on the length of the primaries for increased torque, rather than scavenging at the collectors.
This meant a Loooooooong set of primaries to do the job. In the ideal world, the primaries should be in the range of 30 - 34 inches with an ID of no smaller than 1.5 inches but no larger than 2", and equal length would mean equal scavenging for every cylinder.
So the search went on, and on, and on ..... On the road to utopia, we discovered some interesting designes out there. Borla is a popular one, but here are the facts. Borla primaries are nowhere close to 30" and their unequal length secondaries resulted in untimed exhaust pulses. The only benefit from using short runner unequal length secondary headers are from the reduced backpressure from eliminating the restrictive stock catalytic converters and replacing them with a freer flowing type. No biggie.
Where to find good headers, Maxim Works makes the crown Jewel of them all, Brullen makes a functional but ugly header, and TWE makes nice equal length long primary headers but they are made of mild steel. Also, from Australia MRT makes headers that work quite well.
I bought my self a set of Maxim works headers, cause they fit the criteria I was looking for, but they came with no Catalytic converter, so on to the next topic.
Catalytic converters:
Our cars use 3 way catalytic converters, and no matter which converters you use, you'll get the P0420 CEL code unless you add a 1 Meg Ohm resistor with a 1 microfarad capacitor to the rear O2 sensor. (another story).
3 way catalytic converters use 3 reactive catalysts to control the exhaust gasses and to catalyze the hydrocarbons to harmless CO2 and O2 and H2O. They do this by burning the remaining hydrocarbons through chemical reaction with the Platinum, Rhodium, and Iridium embedded in the catalytic converter. The exhaust out of the catalytic converter is hotter than the input temperature, that's how mechanics check if your catalytic converter is actually working. They use an IR pyrometer and point it to the inlet and exhaust of the converter and see the difference in temp.
Anyways, what's a high flow cat?
Before I get into that, let me tell you about the stock cats, the stock cats are ceramic substrate with extremely fine honeycombe pipettes running in parallel throughout the length of the element. Each cell or pipette is about the diameter if a pin head, and there are hundreds or even thousand of these little pipettes straining the exhaust gasses, our scoobs have 2 of these in the NA version. The pre-cat is a full cat which pre-burns the exhausts and leads them immediately to the second cat where the burning continues. The OEM Catalytic substrate is high quality and will usually last the lifetime of the vehicle if good quality unleaded fuel is used. Otherwise they get coated and clogged. Run them too rich and the cats can melt themselves down.
What about those 100 dollar aftermarket cats? Well put it this way, the aftermarket can make 10 cats out of 1 of our stock cats, which means that 2 of OEM cats can make up to 20 aftermarket quality cats. (Generalization, but it's true)
What is a high flow cat?
By definition, a high flow cat is any cat which flows higher than the stock cat. Which means if you change the inlet and outlet size of the "cheap" cats, you get a high flow cat. I've seen quite a few of those, Random tech sells one for big bucks, Brullen can supply you with a variety of cheap cats. What makes them cheap is they use the similar ceramic type of substrate with tiny pipettes just like the OEM, the only difference is the size of the inlet pipe and outlet pipe.
What's a real high flow cat?
In my books, the only real high flow cats out there are the ones that are called "Metal Core" high flow cats. They are sold in 3 cell sizes, 300c, 150c, 80c. I don't really know what the c stands for, but if you take a look at a typical metal core cat, it looks like a spiral wound cardboard flap, but it's made of metal.
Advantages of metal core: Can't be burned out, will accept anti-lag without a hint of damage, lasts forever, and filters exhaust gasses 140% better than the OEM cats, without the restriction.
Disadvantage: $$$
Net result after spending mega bucks on Maxim Works headers and high flow cat...
Flatter torque and power curve and an increase in the fabled HP of 15 hp, but the most significant gain was the flatter torque curve.
Next Article... in the Zen series... Camshafts!
Note: There will be a surprize later in the series when talking about ignition and fuel curves, and how important it is to extracting the most out of your engine.
4 Stroke-Cycle engines are all basically the same, Intake->Compression->Combustion->Exhaust are the 4 strokes per cycle that occurs at every 720 degree revolution.
Getting back to the Quest for Power. Once again my goal was to increast the available torque and power available for my hobby / sport of Autocross. Which means I need power under the curve to stretch as far as possible, and start as low as possible. I've already installed my 2.25" cat back exhaust, now I need to get rid of my restrictive stock exhaust manifold and stock catalytic converters.
Again, I did research, lots of it to look for the absolutely the best headers for my application. Keep in mind, the 2.5L Boxer engine from our scoobs have a redline of 6250 or 6500 depending on SOHC or DOHC. My car was a SOHC variation with a slightly lower redline, which means at this low rpm range and a volume of 625cc / exhaust pulse (add temperature), I needed a header with fairly long primaries to do "scavengine" within the primaries, relying primarily on the length of the primaries for increased torque, rather than scavenging at the collectors.
This meant a Loooooooong set of primaries to do the job. In the ideal world, the primaries should be in the range of 30 - 34 inches with an ID of no smaller than 1.5 inches but no larger than 2", and equal length would mean equal scavenging for every cylinder.
So the search went on, and on, and on ..... On the road to utopia, we discovered some interesting designes out there. Borla is a popular one, but here are the facts. Borla primaries are nowhere close to 30" and their unequal length secondaries resulted in untimed exhaust pulses. The only benefit from using short runner unequal length secondary headers are from the reduced backpressure from eliminating the restrictive stock catalytic converters and replacing them with a freer flowing type. No biggie.
Where to find good headers, Maxim Works makes the crown Jewel of them all, Brullen makes a functional but ugly header, and TWE makes nice equal length long primary headers but they are made of mild steel. Also, from Australia MRT makes headers that work quite well.
I bought my self a set of Maxim works headers, cause they fit the criteria I was looking for, but they came with no Catalytic converter, so on to the next topic.
Catalytic converters:
Our cars use 3 way catalytic converters, and no matter which converters you use, you'll get the P0420 CEL code unless you add a 1 Meg Ohm resistor with a 1 microfarad capacitor to the rear O2 sensor. (another story).
3 way catalytic converters use 3 reactive catalysts to control the exhaust gasses and to catalyze the hydrocarbons to harmless CO2 and O2 and H2O. They do this by burning the remaining hydrocarbons through chemical reaction with the Platinum, Rhodium, and Iridium embedded in the catalytic converter. The exhaust out of the catalytic converter is hotter than the input temperature, that's how mechanics check if your catalytic converter is actually working. They use an IR pyrometer and point it to the inlet and exhaust of the converter and see the difference in temp.
Anyways, what's a high flow cat?
Before I get into that, let me tell you about the stock cats, the stock cats are ceramic substrate with extremely fine honeycombe pipettes running in parallel throughout the length of the element. Each cell or pipette is about the diameter if a pin head, and there are hundreds or even thousand of these little pipettes straining the exhaust gasses, our scoobs have 2 of these in the NA version. The pre-cat is a full cat which pre-burns the exhausts and leads them immediately to the second cat where the burning continues. The OEM Catalytic substrate is high quality and will usually last the lifetime of the vehicle if good quality unleaded fuel is used. Otherwise they get coated and clogged. Run them too rich and the cats can melt themselves down.
What about those 100 dollar aftermarket cats? Well put it this way, the aftermarket can make 10 cats out of 1 of our stock cats, which means that 2 of OEM cats can make up to 20 aftermarket quality cats. (Generalization, but it's true)
What is a high flow cat?
By definition, a high flow cat is any cat which flows higher than the stock cat. Which means if you change the inlet and outlet size of the "cheap" cats, you get a high flow cat. I've seen quite a few of those, Random tech sells one for big bucks, Brullen can supply you with a variety of cheap cats. What makes them cheap is they use the similar ceramic type of substrate with tiny pipettes just like the OEM, the only difference is the size of the inlet pipe and outlet pipe.
What's a real high flow cat?
In my books, the only real high flow cats out there are the ones that are called "Metal Core" high flow cats. They are sold in 3 cell sizes, 300c, 150c, 80c. I don't really know what the c stands for, but if you take a look at a typical metal core cat, it looks like a spiral wound cardboard flap, but it's made of metal.
Advantages of metal core: Can't be burned out, will accept anti-lag without a hint of damage, lasts forever, and filters exhaust gasses 140% better than the OEM cats, without the restriction.
Disadvantage: $$$
Net result after spending mega bucks on Maxim Works headers and high flow cat...
Flatter torque and power curve and an increase in the fabled HP of 15 hp, but the most significant gain was the flatter torque curve.
Next Article... in the Zen series... Camshafts!
Note: There will be a surprize later in the series when talking about ignition and fuel curves, and how important it is to extracting the most out of your engine.