Apologies for not writing this sooner, but installing the high flow cat has been a small ordeal for me.
The first thing I noticed during the install is that the bottom flange of the cat converter didn't line up with the support bracket on the engine. "No biggie. I'll just rotate it a bit" I thought. Not so much. The bracket has a small tab on it that prevents such rotation. So I used a dremel with cutting wheel to remove said tab. Good to go! Here's the before and after:
Now here's the part that caused me tons of frustration: regardless of what angle I installed the exhaust on the converter at, the connection would leak. On one the last few attempts, I mated the exhaust and cat together first to make sure everything was centered and then installed them as one assembly. Still it leaked. Out of desperation I tried applying a thick bead of copper sealant hoping that would resolve it. Still it leaked. Finally, I gave up and took the car to a muffler shop. Pics of my efforts:
The mechanic used a different (smaller?) donut gasket Correction: The mechanic used the gasket that came included with the HFC and was able to get the connection to seal perfectly with no gap between the flanges. Relief! He must have used impact tools because after taking the taking the HFC off at a later date there was no way I could get the flanges flush again with regular hand tools. I also noticed the sides of the clamp bowed a bit after he did the install. Now onto the driving impression.
First, note that I have the Solo Mach w/ resonator exhaust installed. Before the high flow cat, I absolutely loved every minute of the sound! After the high flow cat, the sound was still nice but took some getting used to. The high flow cat basically doubles the rumble and burble the solo mach exhaust produces. Under heavy acceleration at high RPMs (4K+) the exhaust is downright LOUD; I would say borderline obnoxious even. However, the overall sound is less harsh at lower RPMs compared to with the stock converter installed. With the stock converter, 3K RPM was the most my ears could take when cruising around town. With the high flow cat I can comfortably cruise at 4k RPM if I so choose. Thanks to the resonator in the Solo Mach exhaust there's not even a hint of rasp (whew). Drone is still non-existent when cruising and at part throttle. Idle noise is as quiet as ever. During acceleration and deceleration while in gear is the only time the exhaust makes its presence obvious.
On the emissions front, my car has 6 monitors ready at the moment (evap is not ready). I have yet to get any codes due to the high flow cat either. As far as I can tell, the O2 spacer is doing it's job.
Lastly, I haven't had my car dyno'd again yet so I can't give hard numbers. However, I can say that my car noticeably accelerates faster. For that reason alone the high flow cat has been a worthwhile purchase for me.
