Iggy

I'm getting pretty significant resonance with a cold motor at idle in gear and also in the 1500-2220 rpm range when warm. Cruising down the highway is no problem but around town it's just enough to drive me nuts.

I've tried everything from retorquing the system to disassembling and reassembling and tightening in different sequences. For now I've gone back to a stock setup, but after having a taste of the performance bump in the Vtec rpm range with the DC's, I'd really like to find a solution to this problem if there is one.

I'm thinking I might give DC Sports a call to see what they have to say.

Any suggestions?

justnspace

iTrader: (1)

when you are changing out exhaust pieces, you are experimenting with sound. the only way to find a sound to your liking is to keep playing around with exhaust pieces......
maybe you'll want to add a long resonator, to help quell the resonance...
maybe by adding a resonator; it'll quiet down the whole exhaust to where you want more noise..maybe not. keep playing by adding or deleting exhaust pieces.

gnuts

iTrader: (1)

what's the rest of your exhaust setup?

Iggy

Stock system so I don't have the option of changing things up.

When I say resonance, I'm talking about a loud vibration that rumbles into the cabin. Almost like a REALLY bad heat shield that is loose, but It is definitely not any of the shields.

With the car up on a lift and the engine running, I can feel a vibration throughout the downpipe which seems to be the culprit. I'm wondering if different gaskets might isolate the headers from the downpipe enough to stop the vibration.

justnspace

iTrader: (1)

add the biggest (longest) resonator you can find

gnuts

iTrader: (1)

something seems off. I would try different gaskets like you said. Just headers shouldn't make a huge difference in sound.

Darksyne

Having the same Issue after I upgraded my exhaust. It seems to be intermittent but happens mostly when cold at around 1600-1900 RPM it would sound like a loud vibrating almost buzzing like sound and sometimes it's bad enough that I could almost feel the vibration from the resonance. I'm gonna try and figure out exactly which part of the exhaust is causing it and see if there was a way to tweak the position to fix it.
I have DC headers too so any info on this would help a ton.

Iggy

There really isn't a change in sound, but like Darksyne says, it's more of a vibration that only happens in certain RPM ranges.

Any recommendations on alternative gaskets?

zeta

iTrader: (1)

I used this kit, IIRC'ly, back when I had an exhaust leak at the cat. The one I used did not fit 'exactly' so I had to modify it. It stopped the leak though. YMMV.

https://www.rv6-p.com/gasket-set.html

justnspace

iTrader: (1)

add a resonator...

where does the word resonator come from?
comes from the word resonate!
a resonator will get rid of resonance or try to mitigate it...
it's all experimentation.
try it out.

gnuts

iTrader: (1)

Ya if gaskets don't solve anything I'd place a resonator right after the cat. If you look at the 2nd gen TL, they have a small resonator there where the CL only has the one before the Y split.

Iggy

So add a resonator after the cat AND keep the existing stock resonator or delete the stocker and just replace it with a larger aftermarket?

I'm still trying to wrap my head around how a resonator downstream will stop vibrations in the J pipe.

Darksyne

Might not work because I have a Tanabe cat back too and that has a resonator after the cat instead of straight pipes all throughout. I think it's just the position of the down pipe or gasket adjustment.
Or just replace some of the gaskets with OEM ones I used Fel-pro gaskets for the DC headers and the gaskets included in the Magnaflow Cat for the Converter.

gnuts

iTrader: (1)

I think if it's vibrations, then something is off on the setup. If it's resonance (like a dull hum at certain RMPs) then you need to just put an addition resonator after the cat, keep your OEM one near the Y split.

zeta

iTrader: (1)

Just to recap. A curious question. When you dropped in the J35A3, I presume you installed the header manifolds on the engine first, torqued them down, and then installed the engine. At some point when you were ready, after the engine install, you then placed new 'doughnut' gaskets on the J-pipe and mated it up to the two header manifolds loosely with the bolts/nuts. Then, after placing some kind of gasket material to the junction of the J-pipe/cat, this was then loosely attached with bolts/nuts to hold it all in place. When it came time to finally tightened everything down, what sequence did you use?

Did you first tighten the header manifold ends to the J-pipe and then proceed, finally, to the J-pipe/cat connection or start at the cat first then move to the manifold connections?

MBP 03

I'm experiencing the same thing with my setup and it's definitely a dull hum that is much more pronounced for the first couple of minutes until the exhaust warms up. When I installed the headers, I also swapped out my CA emissions OEM cat first for the XLR8 high flow cat and eventually for a Magnaflow Federal emissions one, so I never ran the combo of DC headers with the OEM CA emissions cat. What I can tell you is that besides there being more of an exhaust smell with the XLR8 cat, there was also a bit more of the resonance, so I decided to leave the Magnaflow cat on for now and sacrifice a few HP for cleaner exhaust and a bit less resonance.

By design, cast iron exhaust manifolds are supposed to quiet down the exhaust, It makes sense that by replacing them with thinner walled stainless steel headers and possibly also a slightly thinner walled J-pipe when compared to stock, you're going to get slightly increased exhaust noise.

FWIW, the DC Sports installation instructions call for the rear header to be fully tightened to the head first, the front header to be loosely installed, then the J-pipe fully tightened to the rear header flange, followed by the front header flange, and finally, the front header gets fully tightened at the head. This is the sequence that I followed and I have no leaks to speak of.

Iggy

The first time was exactly like MBP 03 said, per the install instructions. Tight rear manifold with loose front, then tighten rear downpipe, tighten front downpipe, tighten front manifold, then tighten cat. I've tried different variations with the same result. Either way I've never had any leakage issues, just this damn annoying vibration, hum, resonance or whatever you want to call it.

I agree with MBP 03, the cast iron OEM manifolds absorb a tremendous amount of vibration energy just by their sheer mass and density compared to the aftermarket headers.

zeta

iTrader: (1)

Got it. Well, it sure sounds like you've tried pretty much everything.

The only thing left is the flex pipe enclosed within the flex mesh? Otherwise, it sounds like the '...annoying vibration, hum, resonance...' is inherent to the engineering/materials the headers are made from. And then, of course, there is the 'experimentation' aspect of various resonators, as mentioned above, as a plan B.

Well, there is one other option, in the form of a set of overpriced 'Auto' CT-E headers in the Blackmarket for $900.

Darksyne

And that's used too >.< I remember one time seeing CTE headers for the CL-S Manual without the J-Pipe used sold on ebay for $800 CAD. No way a sane person should pay that much for used parts. Even if it is Comptech.

Darksyne

Iggy

Interesting. I'll look into it and get back atcha. Thanks Darksyne