So I've read just about every thread on HFC's I can find but still have some questions. Basically, I'd like to make my car slightly louder (without adding excessive rasp and drone) and am wondering if HFC's are the best way to go. I am running the Tanabe Axle-back with Vibrant resonators and it really sounds amazing tone wise, but after the break in period and me getting used to it I am finding it to be hardly noticeable anymore unless I really rev it.

Are HFC's the best way to add some volume (and power) without messing up the rest, or are there any other options I can look into? If HFC's ARE the way to go, which ones? I am mostly torn between Kinetix and F.I, but worried the *Resonated* FI HFC will not make a difference and don't see another non-resonated option available online. Did some research into ART pipes as well but probably not feeling the potential smells.
Any help or discussion on the topic would be appreciated, first time posting on the forums but have been reading them for years!

Side note: Yes I know I should have probably just gotten a full CBE and called it a day but these are my first mods so I am just going piece by piece and having fun with it

 

HFCs will definitely give you more sound, but it may come with some rasp…although with your exhaust, you may not notice any rasp at all, tough to say.
I have Kinetix HFC I will be installing on my car hopefully next week sometime, so I’m planning to have a before (Top Speed true dual 2.25” catback) and after video of the car on startup and at idle, with some revving, but don’t plan to do any flybys or fancy stuff.

 

I would only recommend HFC if your cats are failing or you're looking for power.

If sound is what you want, go with CBE's and sell yours.

Tanabe's are a bit low in sound from the general consensus so maybe a muffler change might set you as well.

Many folks end up going back to stock cat when they mix exhaust parts incorrectly.

Now is not the time to ditch your cats since you'd be loosing some MPG even with HFCs

 

Thanks for the well written response. That makes a lot of sense.
My stock cats have 110k on them so I may reach that point in the near future.

I really love the sound of my current exhaust and wouldn't want to switch it completely out, more so interested in seeing if there are any options to boost it with different additional pipe set ups (i.e Y pipes, HFC, etc..). And additional power surely wouldn't hurt. Totally hear you with the mixing of exhaust parts though and could see how that could cause some issues.

 

There was a time when I had resonated HFCs installed, while still using the OEM catback. For about a year, actually. It was an uncommon approach to exhaust mods, but I wanted to baby-step my way into the upgrades, and at the time I was prioritizing gains over sound. The overall volume was increased just a little bit, and the tone of the exhaust deepened. Again, just a little bit. Along with those changes in exhaust note, there was a noticeable bump in power. And while I say noticeable, it was also... just a little bit.

Take that FWIW. Also, those were resonated cats.

 

Do you have some reasoning for this? Factory cats are more restrictive than aftermarket, common thinking is that mileage should increase, if anything.

 

The man the myth the legend! "Just a little bit" is exactly what I'm looking for in this case. Going to order some FI RHFC and try to get them installed a few weeks from now as I've read there is some wait, have heard nothing but good things otherwise.
Also going to add some sway bars while I'm at it.
Excited to see how it all turns out.

 

I agree with this, MPG should either be unchanged, or increase.

Knowing myself, and the feeling like many others here drive just like me, I could see an initial decrease in MPG due to the excitement, change in sound, and power, my foot would be a bit heavier for a bit.

 

did you install your cats yet from kinetix?

 

Yep, and to be perfectly honest it’s a bit too loud and crackly now, but they’re staying, lol

 

make a video when you get the chance I want to hear

 

I only have a idle video so far, planning to make one driving though. Problem is the car was pretty loud before, sounded great actually. So now it’s too loud and I need to reel it in, so it’s better for mileage I guess cuz I’m not hammering on it all the time now, lol.

 

They're more restrictive due to the 300-400 cell count they bring vs 100-200 cell count which most aftermarket cat's bring.

The less cell count the more exhaust they let through and the less efficient the cat is at converting these gasses. This lower efficiency will be picked up by your downstream O2s and will send a leaner mix to the ECM resulting in the ECM making the engine consume more gas to get to efficiency levels.

A perfect high flow cat would be a 3-4 in inlet cat with 300-400 cell count, the increase in pipe diameter will let more exhaust volume and the cell count will ensure these gases are catalyzed properly. A setup like this would have to be custom, custom Catalytic cores range from $50 - $200. You'd have to invest about $600 for a proper job for a Great High Flow Catalytic Converter.

You figure V8 vehicles can make 4-500whp with catalytic converters and pass emissions, our V6s should not have this big of a problem however when you compare the bolt on market most use a 2.5- 3 in lower count cores, these same cores if they were 3-400 count would be too restrictive. Piping size and core inlet need to increase to have both performance and efficiency.

 

Downstream 02s aren’t used really for fuel calibration, they’re more for catalyst monitoring……there’s no need to have 2 02s per side to calibrate fuel trim.
I can’t seem to post a sound clip, so not sure if I need to use a host site, but I’m not gonna do that. I’ll say it’s loud, and raspy/crackly, too loud for my taste actually, but I kinda figured it would be due to my exhaust setup, regardless, I’m not putting the stockers back on.

 

The ECU wants to stay at stoichiometric. It achieves this with fuel trimming based on the oxygen content of mainly the upstream O2. There is no need for a down stream O2 other than to monitor the efficiency of the first catalytic converter, (our second cat is not monitored.) and some small long term fuel trim adjustments.

a internal combustion engine is essentially a big air pump, takes air in, craps air out. The harder it is to take air in and pump it out, will require more fuel to achieve the same result. The easier it is to intake air and exhaust that air, the easier it is for the engine to achieve the same result, thus, less fuel.

If your driving style remains the exact same, a engine which can more efficiently pump air vs one which cannot will result in better fuel economy.

Simple intake and exhaust modifications which do not require any sort of ECU tuning aren’t adding horsepower, they’re simply freeing up horsepower which otherwise would have been lost due to inefficiency. If the ECU was unable to maintain its factory set parameters with a HFC you would have fuel trim DTC’s. The J-turns and anti foulers are added to the down steam O2 so the computer sees an appropriate change in the wave form from upstream to downstream O2. The change it wants to see is achieved by the catalytic converters and has little to do with fuel trimming, that’s all the upstream O2 which are wideband whereas downstreams are shortband. This can be seen on a scope, I’ll see if I can scope my down stream before and after HFC installation.

Remember, oxygen sensors can only measure one thing, oxygen.