2JR 3" Hi-Power Catback Exhaust - $529

[stuntdoogie]

It was checked twice and nothing was rubbing or touching.

 

[iso100]

While it was on the lift or on the ground? Wait for it to cool off then grab the tips and shake vigorously. Does it hit anything?

 

[moshaholic2]

Looks like rub marks going over the rear axle too

 

[Hijinx]

I still want to know about these tunes 2JR spoke of much earlier in the thread.

 

[iso100]

Agreed!

 

[moshaholic2]

Next person that does this install can you take a quick picture and measurement of the rubber exhaust hangers? It will make it super easy for us to hunt down harder durometer exhaust hangers so we can get this exhaust nice and close fitting w/ no rub and little movement.

 

[rodmoe]

I think I might have the old ones laying about..

Like I have said before i replaced these with ones i had left over from a old Acura project I got from Rock Auto they were black and hard as a rock if that helps I think it was a 2002 RSX or the 1990 Integra we built for the track.. Post back when you find something I would like to replace ALL of mine with a known hardness

 

[koozy]

What's the size of the holes for the hanger? 12mm?

these from Kartboy look like they might work. http://www2.kartboy.com/x4/product.php?productid=16163&cat=0&page=1

Center to center holes is 1.400", and looks like that's pretty close to the pics of the stock hangers.

 

[moshaholic2]

these also look like they may work

http://www.ebay.com/itm/Perrin-Perf...Parts_Accessories&hash=item58aafc5d8d&vxp=mtr

75a durometer (which I think is what Group N parts are)

 

[rodmoe]

I'll grab the hole ID as soon as I get home from work tonight..

Ok measured the hole Diameter and even streching it it was only 10MM so 12mm may be a tad loose

 

[Hijinx]

Question: Is it really a good idea to replace the exhaust hangers before replacing the RMM? Seems to be that all that moving about has the potential to damage the exhaust if it's too rigid. Which is probably why the original downpipe has that seemingly ridiculous mount.... Now that I think about it, that mount sort of acted as a stabilizer.

Edit- Where is this tune on 2JRs site?!

 

[stuntdoogie]

Is Joe on a extended holiday vacation?

 

[meFiSTo]

Hmmm. Interesting read regarding stuntdoogie's issues. My 2JR exhaust just got installed, along with a Cobb rear motor mount, this week. I did notice a kind of drone in the mid-range between about 3500 to maybe 4000+ RPM. Steady state under 3000 RPM (typical cruise engine speed) is calm; stout acceleration is as expected. Car is a little new to do too much WOT, but I'm expecting positive effects with that. It's with of a steadily increasing throttle over 3500 RPM that there appears to be a kind of resonating effect (somewhat loud "Huuuuhhhhhnnnnngggg" kind of thing). Just got it, so I'll drive it a bit. Rear hanger was zip tied, but there is still some movement (by hand). I don't commute with the thing so I don't put much mileage in. I'll drive today after work to see what's what.

 

[stuntdoogie]

Hmmm. Interesting read regarding stuntdoogie's issues. My 2JR exhaust just got installed, along with a Cobb rear motor mount, this week. I did notice a kind of drone in the mid-range between about 3500 to maybe 4000+ RPM. Steady state under 3000 RPM (typical cruise engine speed) is calm; stout acceleration is as expected Car is a little new to do too much WOT, but I'm expecting positive effects with that. It's with of a steadily increasing throttle over 3500 RPM that there appears to be a kind of resonating effect (somewhat loud "Huuuuhhhhhnnnnngggg" kind of thing. Just got it, so I'll drive it a bit. Rear hanger was zip tied, but there is still some movement (by hand). I don't commute with the thing so I don't put much mileage in. I'll drive today after work to see what's what.

This "Huuuuhhhhhnnnnngggg" is exactly what i hear and feel inside the cabin. No joy in hitting that rpm range.

 

[iso100]

Must be the passenger cabin's resonant frequency.

 

[meFiSTo]

More about the drone thing...

This "Huuuuhhhhhnnnnngggg" is exactly what i hear and feel inside the cabin. No joy in hitting that rpm range.

Well, I went for a little ride just now (tried to go for a run, but started to rain with a few thunder claps, so just did a quick local loop in the car instead). It's definitely some kind of mid-range frequency-related drone. It's not 100% consistent, but mostly predictable and ranges from around 3400 RPM to around 4200 RPM (varies). Less so the more forcefully I push the throttle (probably because it does not linger at those RPMs). Downhill and decelerating in that range (and a little lower) the drone predictably comes on. It does not sound like a metal-on-metal vibration or a leak. It's a typical hollow drone (I experienced it in the SVT Focus track car with a Borla exhaust, but moreso with the stock exhaust and test pipe).

I found a neat description of drone in a 2011 Audizine thread. This was presented by R&D engineer John Frame from (now out of business) Stratmosphere. Some relevant notes in there about 4-cylinder engines and turbo applications.

First, lets nail down what "drone" is- drone is a frequency that is felt as well as heard, and for the average human, it is most significant between 94hz-125hz. Some people may be more or less sensitive, but that's just human dynamics. As discussed before, sound is the subject byproduct we are discussing, and in that frequency range, it creates a pitch that can be felt. Easy parallel - big speakers at a concert. When you're far away in the back and its loud as hell, thats because the mid and upper range speakers are hammering away. Higher frequencies tend to cut through and over deeper sounds, but travel a shorter distance. But, as you get closer to the big woofers pounding away up front, you start to not hear as much, but instead, FEEL the bass.

Drone is the magic range at which you can both hear AND feel the exhaust sound.

Factory systems do loads to prevent you from hearing this. I can't even begin to cover all of that, but most notable examples include mass dampers, valves, and specially chambered devices, which we'll get to.

Sound travels as a wave. Exhaust gas pulses travel like waves through the tubes.

It's about to get tough right here: The sound that creates drone, that pitch 94hz-125hz, these are long waves. You know how waves have wavelengths, and all that jazz? These pitches are long, basically from 9ft to 12ft long. As the pulses accumulate and travel down the exhaust (lets use a straight tube as a reference), the sound created will be a constant drone at that range. Bends and resonators help by breaking up the pathway of that wave, and absorbing the actual volume of the wave... but the low frequency tone is still there.. which is how you can have quiet exhaust that still drones. That sucks. Also, that's sometimes why louder exhaust doesn't seem to drone; you let the high frequency waves cut above it... like back at the concert reference we made before.

The best way to cut down the drone is via destructive interference. What you need to do, is reflect the trouble-causing wave back at itself, 180* out of phase.

This is like two equal people pushing an object in opposite directions- nothing happens!

However, that effectively means you need a chamber that can reflect the wave back in a straight line for 4.5 - 6ft. First up, thats difficult under our cars, to have dead tube space like that. One of the easy ways to do it would be to have a muffler or resonator that had a dead stop in a straight line down the center of the car, but the world will assume it can't flow well enough to work. This is the balance between power/flow and sound/comfort. It's always a balance.

Take APR for example, they use RSC technology. They are licensing this from Corsa, which is awesome, because Corsa has a patent on it. Because it works pretty well. What they do, is create that long length of tubing INSIDE a smaller canister- tough to manufacture as well- but it creates that destructive interference. If you've been in a car with a proper RSC system, you know what this is like- you hear the tone that should cause drone, but it doesnt. You don't feel it.

There are other ways to kick that drone though. Take for example, that listed Stratmosphere exhaust- there's a mini magic trick happening in the center resonator, which works awesome on a B7 A4 because of the long straight length of tube created by the DP/center section. Where the exhaust gas splits to go to duals, its in a perforated "Y" piece.. so the waves can travel through it, hit the back of the resonator, and travel backwards (as a wave, not as exhaust gas pressure) oh, I dunno, from about 4.5-6ft right back towards the source!

So basically, there are ways to cut down drone that you can't see. There are loads of ways to deal with it.

With the mustang, using different size mufflers is just another trick. But it's not always the answer. I know older mustang guys used to claim that having two 26.5" long tubes welded at 90* off a section before the muffler would also eliminate the drone- all sorts of ways.

What further makes things interesting, is how different cylinder configurations create drone at different ranges, but all the same (to an extent).. You can calculate out where 4, 6, 8, 10, 12, 16 cylinder configs will drone. I am trying to remember without digging through documents (As this is all off the top of my head), but 4 bangers create the 94-125hz pitches between 3500 and 4500rpm. Add a turbo to the mix, and its more difficult to sit at that RPM range while cruising. So often, you can have a system that is minimal, large diameter, and flows well, without having intrusive drone.

What sucks, is 6 cylinders. They create the 94-125hz tone between roughly 2450 and 3250rpm. Riiiight around the range you'll likely be cruising at on the highway. This also primarily explains why BMW has some of the fanciest tricks for exhaust stuff from the factory, what with a plethora of 6 cylinders along the lineage. It's also why the B8 S4 has light drone BONE STOCK!
8 cylinder motors are easier, as the pitches occur low, like 1850-2450rpm, which in say, the 4.2L, is barely moving along.

No, swapping various Brands mufflers will not likely be the answer. And if it was, it'd be a total fluke. A more interesting scientific test would be to make sure an exhaust system could handle full flow out of only ONE side of a dual exit exhaust.. and then cap off the other side... that'd create your long reflecting chamber..

Anywho- the point is, it is all about waves, and how to bounce them around. You might not see how it's done. And yes, true, not every aftermarket company bothers- but the ones that do, typically are worth the cash.

With all that in mind. This does not bother me so much as the true cruising range is under 3000 RPM (like 2700 RPM) and there's really no drone at all there. So this, for me, should not be a problem on a "trip" (like a the ride to Shelton or Porland) for a track day. Definitely not a problem at the track (which might be why Joe does not notice it so much).

 

[rodmoe]

Good read on the Audi makes a lot of sense and it looks cool when you are done at the track and the inside of your exhaust tips are white

 

[stuntdoogie]

On along distance trip this can be torture. Doint 80 at 3k rpm that right around when the drone starts for me.

 

[meFiSTo]

On along distance trip this can be torture. Doint 80 at 3k rpm that right around when the drone starts for me.

Well, I've not gotten the car up there yet (only 276 miles) and no long drives. That could be a problem, but maybe will mostly limit cruise speed.

 

[spangenb]

Was discussing this resonance problem on another forum with stuntdoogie so I joined up here too. I have the stainless system and really my drone starts as low as 2500 rpm and goes just over 4k. Climbing hills on the interstate it's pretty loud inside the car so pretty annoying :-( It only happens with part throttle. Under hard acceleration it gets much quieter. At its worst the resonance is so bad that the frequency distorts and I can't gage the engine RPM by the sound. We have been trying to figure out the common thread here. Who else has the stainless system?