Low RPM Drone

I installed the Invidia Q300 catback that I bought used the other day and it is too loud for me between 1500 and 2000 rpm. It's already broken in so I think that is not the issue. It seems like there is some sort of resonance where right at 1500 rpm it gets twice as loud even at part throttle, and by 2000 rpm it quiets down to a reasonable level.

 

What is the best way to deal with this? I have done a bunch of research on side branch resonators but it sounds like this might be too big of an rpm range - does anyone have experience with this?Should I just put another muffler/resonator in the system or would that quiet it down all over?

 

I love the rumbly sound at startup and the roar at WOT at above 2k rpm so I'd like to not lose that if possible.

Any thoughts?

 

Thanks guys!

Just a couple of thoughts. Make sure all your connections are tight, no gaps. Also, make sure no part of the exhaust is touching anything underneath. I never had any problem except it is a little throaty at cold idle. Also, I had a stock cat. Not sure if that would make a difference.

I'll take another look for sure. I think this has to do with being paired with my Nameless DP because it gets ridiculously loud just in that short range; it's relatively moderate and enjoyable at all other ranges.

This cannot be normal, at 2k rpm in 4th gear in the city at like 1/10th throttle, I can't hear my fiance talk.

at 2k rpm in 4th gear in the city at like 1/10th throttle, I can't hear my fiance talk.

 

This may be a feature you want to consider at appropriate times.

This may be a feature you want to consider at appropriate times.

 

:lol:

That the sound a 4 cylinder engine makes, primarily, about 50 hz or so at 1800 RPM. Thats why 8-cylinders don't drone, since they the resonant frequency at low RPM is twice as high and much easier to cancel out in a resonator (since shorter wavelength).

 

Are you sure its "broken in" ?

 

Because when I got my Q300 new, it was a few thousand miles of flogging it before it quieted WAYYYYY down. I thought it was way too loud too and now I can hardly hear it other than cold starts.

 

Since you have a Nameless downpipe, which uses a donut flange (right?), have you used a donut-to-flat flange adapter or did you do the shortcut "clamp them together and hope for the best" approach?

 

You may have a leak at the flange, if so.

Well the previous owner ran it for more that 1k miles so unless he's lying...

 

The nameless dp ends in a 3 inch flange that matches up perfectly to the catback. I had to use the grimmspeed adapter for the stock catback, but I have no doubt that these match up.

 

My calculations indicated that it would be 56.66-66.66 hz for that range. I listened to that on Youtube and think that sounds about right. I guess I could get an ap to confirm.

 

I'll check all the connections when I get back into town, but wouldn't a leak give me more noise all the time?

OK, so it has a flat flange that mates up to the Q300 flat flange? I was thinking it had a donut flange, but that's good news.

 

1000 miles isn't enough. And if he took it off because he thought it was too loud then he hadn't broken it in either. It'll take probably 5000 miles. Less if you make more carbon.

 

Go bag the shit out of it for a while. Rich, full throttle exhaust will get you there faster

 

Seriously. Steel-wool packed mufflers need to get loaded with carbon before they work at full effectiveness.

 

Its really night and day how much it will quiet down. If you look back there are threads where I was flipping out about this and about to go off building j-pipes to cancel the drone, and then soon after it just went away.

Im assuming you went with the no cat downpipe instead of the hi-flow cat downpipe? I had a terrible drone on mine at around that rpm range before I put the cat on, and the high flow cat got rid of it.

OK I found the thread in the classifieds archive, he says he had it on the car for 15k. Do you think it will continue to quiet down?

 

The most annoying time is driving in my condo complex, I can either drive in second gear and use the clutch at every turn and bog the engine like crazy at 1k rpm, or have it in first at 2k rpm and be that guy and roar through like a harley.

 

I read through your Q300 thread and a million other exhaust threads on here and did not find someone reporting a similar issue. I did find one Evo IX owner who had something similar but their forum didn't help him out and he ended up putting his stock exhaust back on.

Im assuming you went with the no cat downpipe instead of the hi-flow cat downpipe? I had a terrible drone on mine at around that rpm range before I put the cat on, and the high flow cat got rid of it.

 

dp has a high flow cat.

Hmm ok.. if it has 15,000 on it then it's probably not going to quiet down any more.

 

You can always go the J-Pipe route. Its inexpensive and easy to do. Just need to calculate the right length. I think I had a spreadsheet to figure that out. You need to T off a pipe with a flat end cap that is 1/4 wavelength of the primary resonant frequency causing your drone.

Here you go:

 

J-Pipe Calculations

 

Having the "J" bend in the pipe is optional but gives it a broader range of frequency effectiveness since the effective length changes across the cross-section of the pipe due to the 180-degree bend. Using the same width pipe as your exhaust is important. just T it in anywhere. You can do more than one at different lengths too, or T off one pipe with a few T'd off capped pieces at different lengths to cover a range. You might want to target 53", 56", and 59" length from opening of your exhaust to end cap. All with sealed flat end caps.

 

If you T once and then split 2, 3 ways, etc, you want to T off the main exhaust then y-split to the secondary resonator pipes. Lengths, if done this way, would be T to tip. It could be relatively compact that way all three bundled together.

how big of a range does that affect? It looks like I would want a 50-60 inch pipe. Would I need several?

Updated my post above.

 

I haven't done it but I researched it quite a bit and I know the guys with Cylinder deactivation small blocks in their GM and Dodge vehicles do this with great success.

 

This is what I am talking about:

 

http://solo-performance.com/wp-content/uploads/2011/09/cmm-install.jpg

 

Don;t be confused by references to "J Pipes" on the likes of Cobb's site or other subaru people who seem to refer to the mid-pipe as a j-pipe.

 

The trick is to have a sleeved piece at the end of the j-pipe that you can adjust the length to fine tune it. Then once you have it nailed down, get it welded. You will probably need to cover 1700 - 2000 RPM if I recall my situation.

Oh.. and make sure the pipe is mandrel bent, and that they will drain and not collect full of water.

Okay, update:

I have done tons of research and spent a couple of weeks waiting to see if I'd get used to this. I did not... So I ordered a vibrant ultra quiet resonator and their 12" bottle resonator on Amazon, should arrive Wednesday. (both 3")

My research indicates that since they're straight through, I will still get a nice roar at wot, but my idle might be near silent after this, which is fine for me.

FYI, I have had the best luck finding evo and audi owners with similar issues. wrx searches are damn near useless since 99% concern uel headers.

So my question: Is there any reason to go to a nice exhaust shop to have these welded in?

I am torn between paying more at FAT or PPE Engineering vs a ghetto place for cheap.

Ghetto the shidoutuver

I bought a brand new Q300 and I wish it wasn't as raspy. I hope when it breaks in it'll get a lil deeper. Question for you guys, is it the quad tip that's making it so relatively quiet?

The Q300 doesn't have quad tips....

The Q300 doesn't have quad tips....

 

 

https://www.rallysportdirect.com/part/cat-back-exhaust-system/inv-hs05sl1gt3-invidia-q300-catback-exhaust

Brandon, that exhaust design is ingenious. You can tune the exhaust to your liking then weld it. I think I saw someone with a Pontiac G8 do the same thing to prevent drone. I might just do it right before the resonator like Fredrik. I wish there was a good axle-back I could throw on in the meantime that's not raspy/drone-y. The Megans for the WRX didn't sound too bad. They're about $350 I think.

https://www.rallysportdirect.com/part/cat-back-exhaust-system/inv-hs05sl1gt3-invidia-q300-catback-exhaust

 

Those aren't for the fifth gen.

Okay, update for closure:

 

I got both the Vibrant Ultra Quiet resonator and the 12" bottle resonator welded in.

Initial impression: Perfect. It's about 10% quieter most of the time and there are no more rattles in the car at all. The overall tone is a tad deeper, but as soon as I start to build boost it sounds fantastic, like before I had them welded in.

At idle, it's now only as loud as stock, but way deeper. Cruising on the freeway at 3k rpm it's only a little quieter than with just the Q300.

 

Since these both have steel wool packing I expect that it will quiet down a little more as they break in.

 

I was kind of unsure about putting the resonators in because it might quiet down the exhaust all across the board but that is not what happened. Maybe it's because it is straight through, but it gets just as loud at it's loudest but is quieter when I'm not getting on it.

 

Also, only 45 bucks to get them welded in!