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Intake & Exhaust Questions and info regarding various aftermatket exhaust systems for the G35 (Headers,Y-Pipes, and Cat-Back Systems)

HFC Diameter vs volume question

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Old 01-17-2018, 08:04 PM
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HFC Diameter vs volume question

It may have been answered already, but I couldn't find any information anywhere. I currently have 2.5" FI RHFC into a full Tanabe CBE on my coupe, but realized just how loud it is from outside the car whenever I touch the fun pedal (not straight-piped Mustang loud, but enough to turn heads, which isn't quite what I want. It's also deep at low RPM, almost too deep for me; I like a slightly more restrained sound). I've done some reading and see that the Kinetix HFC (just taking an example, I don't know much about Kinetix) is a 2.25" HFC. That would fit my system better, as right now I'm going 2.5" from the HFC to 2.36" on the Y-pipe which expands to 2.75 midway down the Y-pipe all the way to the tips.

Would going from the 2.5" FI RHFC down to the 2.25" Kinetix HFC have a volume impact? I would probably gain a little bit of rasp due to losing the resonator, but I feel like the decrease in diameter would offset it/reduce the volume. Am I correct in this assumption, or totally wrong?
Old 01-20-2018, 02:20 AM
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High flow cats won't muffle the sound as well as stock. Adding another resonator to your exhaust might help and be a lot less expensive.
Old 01-20-2018, 03:25 AM
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Originally Posted by Scottwax View Post
High flow cats won't muffle the sound as well as stock. Adding another resonator to your exhaust might help and be a lot less expensive.
I'm just wondering if a 2.25" HFC would be quieter at all than a 2.5" HFC, or if the volume change wouldn't be noticeable. If it doesn't make a difference, I was planning on adding a resonator/replacing the small Tanabe one.
Old 01-20-2018, 07:35 AM
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Decibel level isn't determined by diameter so no, frequency however, WILL change.
Old 01-20-2018, 09:20 PM
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Oh, you also have the Tanabe...not particularly loud but the drone on part throttle acceleration and at 2500 rpm was pretty bad. Swapped the muffer itself for a Dynomax Super Turbo, helped a lot. But probably going to end up getting the Vibrant ultra quiet resonator to get rid of what's left.
Old 01-20-2018, 10:40 PM
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Originally Posted by [email protected] View Post
Decibel level isn't determined by diameter so no, frequency however, WILL change.
Got it; the hassle to trade my FI RHFC for someone's 2.25" HFC's in good condition wouldn't be worth it then, considering the tiny impact it will most likely have. Guess I'll look into swapping/welding in a resonator like Scottwax said, or maybe a small box-muffler if I really feel like toning it down. Thanks guys!
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Old 02-25-2018, 08:49 PM
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Originally Posted by [email protected] View Post
Decibel level isn't determined by diameter so no, frequency however, WILL change.
Necroing this, as I need some clarification. So, if my exhaust magically shrunk from 2.75 inch diameter to say, 2.25 inch diameter, would the current exhaust drone stay in the same(ish) RPM range but simply go up in pitch? This is assuming the structure of the exhaust would remain the same.
Old 02-25-2018, 10:14 PM
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Does Tanabe offer silencers with their exhausts? I have the Greddy-Ti dual exhaust that came with silencers and they worked great.
Old 02-25-2018, 11:11 PM
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Does Tanabe offer silencers with their exhausts? I have the Greddy-Ti dual exhaust that came with silencers and they worked great.
They do offer tail end silencers, but (a) not a fan of drilling holes in those beautiful rolled tips, (b) silencers can make everything sounds kind of buzzy to me, although that was with a cheap ISR single and (c) been considering a different catback to get a bit higher pitched sound (and avoid scraping, the Tanabe hangs loooow), so don't want to spend on something I won't keep. Still, I supposed I could paint the front of the silencer black to hide it and have a shop professionally install it.
Old 02-26-2018, 06:25 PM
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Quote:
Originally Posted by Scottwax View Post
Oh, you also have the Tanabe...not particularly loud but the drone on part throttle acceleration and at 2500 rpm was pretty bad. Swapped the muffer itself for a Dynomax Super Turbo, helped a lot. But probably going to end up getting the Vibrant ultra quiet resonator to get rid of what's left.
The OP has a coupe so it might not be as easy to swap the muffler for him as it is for us sedan guys.
Old 02-27-2018, 03:11 PM
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The OP has a coupe so it might not be as easy to swap the muffler for him as it is for us sedan guys.
I have found a 2.75 inlet/outlet Vibrant resonator, one of the flatish/box shaped ones. Space is tight, but it might fit as a swap for the rather small Tanabe resonator. Could always just weld it in later on in the midpipe, but I'm averse to cutting up exhaust. Would rather just go the silencer route, at least that doesn't leave much of a mess if I reverse it.
Old 02-27-2018, 07:07 PM
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The Virbrant resonator is far superior to the Tanabe one, plus it is the full diameter all the way through, the Tanabe resonator necks down to about 1.5" internally. It's a piece of sh*t IMO. The exhaust sounds MUCH better now with the Vibrant resonator. Quieter at cruising speeds, cleaner and meaner at full throttle. Much, much happier with the exhaust now.

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