- - High flow cat- +20whp?
(https://www.rx7club.com/3rd-generation-specific-1993-2002-16/high-flow-cat-20whp-630891/)
Kento
03-14-07 10:39 AM
Originally Posted by Speed of light
Based on actual flow bench work that I have done, I can tell you that most high-flow cats have no advantage over the stock cat, even with its smaller 2 1/2" pipe and restrictive weld beads. This is because the stock cat has substantially more core area than the higher flow cats.
The most restrictive parts of a stock FD exhaust system in order are: 1) the metal precat followed by 2) the main [cat-back] muffler. The stock main cat is 3rd on the list, and finally at 4th is the stock 2 1/2" tubing.
Not sure which hi-flow cats you have flow bench tested, but when looking at the brick in my N-Tech hi-flow cat and comparing it to the stock cat's brick, there is a substantial difference in the honeycomb "density" (number of holes per square inch). The stock cat's brick may be larger and have more core surface area, but the hi-flow cat (at least the N-Tech I have) has better density and also less core length, which affect flow.
Every two years when I have to get my FD smogged, I reintall the stock cat, but leave everything else in the exhaust intact (DP and Racing Beat CB). There is a noticeable difference in power, both in response at lower rpms, and at higher rpms/boost after the secondary transition, and boost ultimately reaches 1 psi or so higher.
Touge Monster
03-14-07 01:17 PM
When I went from the stock cat with almost 100K miles on it to a Bonez 3" high flow I noticed a large difference in power and the power delivery was much more smooth and responsive. The stock cat also weighs a lot to say the least so the weight savings is another great benefit to the high flow unit. I have passed Cali smog twice with the 3" cat with below average emissions each time.
wstrohm
03-14-07 01:46 PM
I had a slight out-of-spec smog test with our original cat in 2002. None of the "standard" fixes (plugs, wires, making sure engine was hot, etc, etc.) worked. Replacing the old OEM cat with a brand new Bonez high-flow resulted in a way out-of-spec result. Buying and installing a new OEM cat fixed everything. I think the air injection of the OEM is carefully designed inside the cat to make sure all of the active catalyst "sees" the injected air. The Bonez probably just blew air into the casing without distributing it properly.
rynberg
03-14-07 01:54 PM
I passed just fine with a new streetported motor (200 miles) and the Bonez hi-flow cat....
Touge Monster
03-14-07 05:24 PM
Both times I passed smog with the Bonez cat I didnt run a pre cat btw...
illusionzx
03-14-07 05:53 PM
all this talk, i just pay a guy to pass my car during inspection time.
