High flow cats and horsepower
The exhaust volume an engine produces is a lot greater than the volume of air that it takes in due to how hot the exhaust gasses are (thermal expansion) so you can't go by how much air an engine takes in.
Cats of same/similar shape and design flow better with less restriction. Here's testing form InstallUniversity.com ... look at the holes per inch. The stockers are 400 holes-per-inch. The other aftermarkets flowed better with less holes-per-inch:
Table 1
Table 1
Inlet Diameter (in.)
Outlet Diameter (in.)
CFM @ 20.4” H2O
CFM @ 28” H2O
Outlet Diameter (in.)
CFM @ 20.4” H2O
CFM @ 28” H2O
Passenger Side Catalytic Converter
2.5
2.5
299.5
350.9
Driver's Side Catalytic Converter
2.5
2.5
268.3
314.4
TTS Bullet Catalytic Converter
2.5
2.5
277.1
324.6
Carsound Catalytic Converter
2.5
2.5
372.7
436.7
FLP Catalytic Converter
2.5
2.5
376.0
440.5
2.5
2.5
299.5
350.9
Driver's Side Catalytic Converter
2.5
2.5
268.3
314.4
TTS Bullet Catalytic Converter
2.5
2.5
277.1
324.6
Carsound Catalytic Converter
2.5
2.5
372.7
436.7
FLP Catalytic Converter
2.5
2.5
376.0
440.5
Jeb: You are missing what people are saying. Holes per inch is NOT a measurement of flow or performance.
If you look at installuniversity, they measure CFM which IS a measure of flow.
If you go and read the Random Tech link that someone else posted, you will see how they explain that holes per inch is doesn't mean much because of differences between manafacturers design. They explain it much better than I can.
You need to compare CFM to CFM at the same testing pressure in order to make any conclusions about which converter flows best.
You are right that in "general" less holes per inch does mean the converter will likely flow better but other that generalization, that data between one manufacturer and another is not comparable. In addition, the cat still has to perform it's function of passing an emissions test. A high flow cat that fails the test is useless.
A lot of manufacturers don't even publish CFM figures because they don't want you to know. They just call it a high flow cat and people will buy it (like the TTS ones install university tested).
Thanks
If you look at installuniversity, they measure CFM which IS a measure of flow.
If you go and read the Random Tech link that someone else posted, you will see how they explain that holes per inch is doesn't mean much because of differences between manafacturers design. They explain it much better than I can.
You need to compare CFM to CFM at the same testing pressure in order to make any conclusions about which converter flows best.
You are right that in "general" less holes per inch does mean the converter will likely flow better but other that generalization, that data between one manufacturer and another is not comparable. In addition, the cat still has to perform it's function of passing an emissions test. A high flow cat that fails the test is useless.
A lot of manufacturers don't even publish CFM figures because they don't want you to know. They just call it a high flow cat and people will buy it (like the TTS ones install university tested).
Thanks
What formula? There is no formula that shows holes per inch and flow. Just because they have less holes per inch doesn't mean the flow more. That's like saying 230cc heads must flow more than 210cc heads, while they should it's not always true. There are too many variables with cats, materials, manufacturing process, how thick hte material is, what kind of material is used, ect. You would think they would come out and say how much the cats flow instead of just stating the holes per inch.
The 10" bullets I bought from them def flowed better than first cats I bought from them.
