Disgustipated

That may be true, but here's my experience:

OEM header = pretty quiet
Aftermarket headers = varying levels of quiet, usually opens up the exhaust note and makes it louder, sometimes more aggressive

Stock cat + aftermarket exhaust = varying levels of drone, sometimes unbearable amounts
Straight test pipe + aftermarket exhaust = less drone, varying effects on exhaust note, tone and loudness, may increase rasp
Resonated testpipe or high flow cat + aftermarket exhaust = even less drone than straight pipe TP, less rasp than straight testpipe, deeper tone vs straight test pipe while being quieter

These are just my experiences hearing my car, various combinations of other cars' exhaust systems and reading on various makes/models + methods of eliminating rasp/drone.

Those are my thoughts and opinions so others may disagree, but I personally think the stock cat with aftermarket exhaust causes drone due to the design of most aftermarket exhausts. For example, I believe one of the Amuse exhausts has a Helmholtz resonator and is as drone free as the stock exhaust. Most aftermarket exhausts do not have a Helmholtz resonator or something equivalent in addition to the regular resonators, instead just having one standard resonating chamber.

From what I can tell, this lack of focus on reducing drone/noise that most aftermarket exhaust designers have causes a 'sound 'bottleneck' that gets caught right in the stock cat (which has far more restriction than a testpipe or high flow cat) and induces drone with the amount depending on the exhaust. Note that the cat is right underneath the cabin of the S2000. In my theory (), this bottleneck with the stock cat increases the occurrence of the frequencies that were previously smoothed out with a stock exhaust and resonates them right into the cabin.

This is why a HFC (resonated) and a resonated testpipe seem to cause the least amount of drone, since they damper those frequencies and filter them out of the cabin.

Disclaimer: This is just my little theory and I'm sure someone with experience in sound theory and how various sound waves and frequencies occur/resonate could blow this out of the water, so take it with a grain of salt.

So I'm not disagreeing with you, gernby, just meeting you halfway and hashing out my own thoughts on the matter.

Disgustipated

Pic added, please see first post.

whiteflash

Bilsteins, Asura...

Can't say I don't like your style

Gernby

Walking on egg shells???

I wonder if Asura would be willing to make an HFC with a 63.5mm input and 70mm output. As I've been testing all these combinations of headers, TP's, HFC's, and exhausts, it's become clear that hard transitions in diameter really reduce power. So it seems like it would be best to eliminate any changes in diameter that you can. Since you have a 3" exhaust, obviously it would be best to have the back half of the HFC to be 3". However, I don't know of any headers with a 3" output, so it seems like it would be best to have the front of the HFC match the header (63.5mm?). Let the only transition in diameter occur at the catalyst ...

Squirtle

Hytech has a 3" output header I believe.

Disgustipated

That's a good point, the header needs to be able to feed such a large exhaust. I just put on my OEM header and took out my DC Sports header. I believe the endpipe of the DC was 2.5 inches, and the OEM is 2 inch.... and i've made more power in certain areas of the powerband...

So how well designed the header is makes a big difference (obviously), and i'd be really curious to see how much power a 3" header mated with a 3" exhaust would make.

@gernby: Asura will make you whatever you want, i'm sure different diameters on each end of a HFC would be no problem. He reads your posts btw and we all agreed that you make excellent posts and bring a lot of info to the table. so i'm surr he'd be willing to work with you and create a unique piece like that. the results would be interesting...

Kermdaddy

OP asked this topic to be moved, so

Disgustipated

Thanks Kerm! i thought this would be more appropriate in the modifications forum since it's a review of a part which most people should know about.

thomsbrain

I think it's cool for the bling and all, but don't get too excited about power gains.

Whiteflash (posted earlier in this thread) and I have the same intake and header, our cars were tuned by the same guy on the same dyno, and we both have aftermarket exhaust. I have the stock cat, he has the Asura. He makes 1 HP more than I do. Differences from engine to engine or even ambient air temp would make a bigger difference.

Disgustipated

1 HP more... at peak? In the mid-range? How does his mid-range compare to yours? You're running a 70mm exhaust with a 3" HFC? I'd be curious to see dyno chart differences.

Read this thread for more information on why a 70+ mm tp/hfc is far better than a stock cat.

https://www.s2ki.com/forums/index.php?showtopic=842575

There ARE big gains, especially if tuned for.