Doug Thorley Cat Back Droning

[Daskoff]

Just had the cat back system installed. The system is beautifully made and easily installed. The gripe I have is with the loud highway droning -around 65-70 mph. Around town driving - sounds great except when pushing the loud pedal anywhere above 2k RPM. I've read all the DT cat back reviews on this forum and looked at the videos on here as well as on youtube. My system is much louder with all the windows up then what I thought it would be from the videos. I realize the videos may have quality issues but still it is loud. I will try and post a video with the inside noise.

Question I have for those that have the system, has the sound mellowed out over time/miles? Has anyone put a resonator after the muffler? For now I will drive with it and maybe I will get used to it. Worst case I may change out the muffler for something quieter.

I am getting ready to pull a trailer to Sturgis so I hope it does quiet down some.

 

[pawwright]

I'll get a drone around 1700-2000rpms or so when on a load or going uphill - no issues otherwise..... I can hear it most times driving, but it's not bad..... only around the 2500rpm mark will i get a tinny sound, and only for that time of going uphill or with a load...

 

[landylover21]

My peak resonance is around 1,800-2,000 RPM, where it's noticeable. Driving around town it's not noticeable, although I had the Borla system installed previously so I may be used to things being loud. At 65-70 MPH, there is a slight drone but it's mostly hidden by road and wind noise.

There are days when I want to quiet it down sometimes especially driving around town... every throttle input is noticeable and the resonance at 1,800 RPM can get annoying. I've been thinking about getting a tip welded on that protrudes from below the bumper like OEM as a couple friends have said the turn down tip amplifies everything in the cabin. Other than that, it's not bothersome (to me at least - my mother who is used to quiet hates it).

Did you come from an OEM exhaust? My original OEM rotted out internally so I looked at options, and initially bought a Borla system that was drony but definitely not as loud as the Doug Thorley, then bought the DT system last October, so I was used to hearing that extra volume. I'm sure if I came directly from an OEM exhaust I'd perceive it as much louder.

As far as it quieting down over time, I haven't noticed any appreciable difference in volume in the 10 months that I've had it now.

 

[Daskoff]

My peak resonance is around 1,800-2,000 RPM, where it's noticeable. Driving around town it's not noticeable, although I had the Borla system installed previously so I may be used to things being loud. At 65-70 MPH, there is a slight drone but it's mostly hidden by road and wind noise.

There are days when I want to quiet it down sometimes especially driving around town... every throttle input is noticeable and the resonance at 1,800 RPM can get annoying. I've been thinking about getting a tip welded on that protrudes from below the bumper like OEM as a couple friends have said the turn down tip amplifies everything in the cabin. Other than that, it's not bothersome (to me at least - my mother who is used to quiet hates it).

Did you come from an OEM exhaust? My original OEM rotted out internally so I looked at options, and initially bought a Borla system that was drony but definitely not as loud as the Doug Thorley, then bought the DT system last October, so I was used to hearing that extra volume. I'm sure if I came directly from an OEM exhaust I'd perceive it as much louder.

As far as it quieting down over time, I haven't noticed any appreciable difference in volume in the 10 months that I've had it now.

Yes - I came from OEM exhaust which was also rotted out but not leaking. I'm going to see how I get used to it on this road trip - unfortunately it is 1,800 miles round trip with a trailer so I imagine I will have to be on the throttle quite often. I may try to find a short resonator I can put on after the muffler or worse case I would replace the muffler with something a little quieter.

 

[costalcat]

I have this system on for about 10,000 miles right now. That drone doesn't really mellow out when I'm pulling my trailer it actually gets a little noisier with the load on. 65-70 is where I'm having a weird sound that has started and after a lot of research I think I have it down to the exhaust system. I think I have a leak at the first bend coming back... but I have been happy with the system....

 

[GregLCA]

Just had the cat back system installed. The system is beautifully made and easily installed. The gripe I have is with the loud highway droning -around 65-70 mph. Around town driving - sounds great except when pushing the loud pedal anywhere above 2k RPM. I've read all the DT cat back reviews on this forum and looked at the videos on here as well as on youtube. My system is much louder with all the windows up then what I thought it would be from the videos. I realize the videos may have quality issues but still it is loud. I will try and post a video with the inside noise.

Question I have for those that have the system, has the sound mellowed out over time/miles? Has anyone put a resonator after the muffler? For now I will drive with it and maybe I will get used to it. Worst case I may change out the muffler for something quieter.

I am getting ready to pull a trailer to Sturgis so I hope it does quiet down some.

You could always play around with the idea of welding a Hemholtz resonator (basically a J-tube) near the back of the exhaust to create a cancelling effect on the specific frequency of the drone you are chasing. It would be a bit of trial-and-error to figure out the correct tuned length that would work best, but if you "sleeved" the J-Tube out of two pieces of tubing (think: slide trombone) you would be able to adjust the length easily......drive.....test/listen.....then re-adjust until you got it perfect. Remove the temporary tube clamp and fully-weld at the final length.

I'm not saying it's easy, but if you have a welder (or a friend with one) you might be able to solve your drone pretty cost-effectively.


-G

 

[Batlowboy]

Get rid of the drone by putting a full exhaust system on, extractors, high flow cats and 3 inch pipe the whole way through, let the old girl breath. A cat back system really only achieves a little more noise, you need to open it up the whole way, including letting it get more air into the engine via a snorkel.

 

[Daskoff]

You could always play around with the idea of welding a Hemholtz resonator (basically a J-tube) near the back of the exhaust to create a cancelling effect on the specific frequency of the drone you are chasing. It would be a bit of trial-and-error to figure out the correct tuned length that would work best, but if you "sleeved" the J-Tube out of two pieces of tubing (think: slide trombone) you would be able to adjust the length easily......drive.....test/listen.....then re-adjust until you got it perfect. Remove the temporary tube clamp and fully-weld at the final length.

I'm not saying it's easy, but if you have a welder (or a friend with one) you might be able to solve your drone pretty cost-effectively.


-G

This is exactly what I did. I could only fit a 25" pipe right after the rear axle. I haven't tried highway speeds but the 25" pipe did get rid of the drone at 2000 rpm. It also quieted down the overall sound. So far I am pretty happy with the pipe addition. It doesn't look great but it does work. I will report back after my trip.

Thanks

 

[pawwright]

This is exactly what I did. I could only fit a 25" pipe right after the rear axle. I haven't tried highway speeds but the 25" pipe did get rid of the drone at 2000 rpm. It also quieted down the overall sound. So far I am pretty happy with the pipe addition. It doesn't look great but it does work. I will report back after my trip.

Thanks

Nice - I'd like to see a pic if you get some free time.

 

[Daskoff]

Nice - I'd like to see a pic if you get some free time.

Here you go - per info I glean from the ole interwebs the bends should be mandrel bends and much smoother. I needed it fast and this fixes what I wanted and it cost me $150 at a local muffler shop. It really is amazing, not only did it get rid of the droning but also quieted the overall system. You can still definitely hear the exhaust but not every little accelerator input. Still haven't tested it on the highway but I will report back as I am going to trailer a couple of bikes to Sturgis starting tomorrow.

Also please don't mind the rust on the frame - I only had this truck for a few months and have already sunk a ton of money into it. Next on the list this fall will be the underbody rust which I will treat with a rust convertor and then POR15 or something like that.

Back to the main issue. Yep dosen't look exotic but it certainly works and am happy with the sound now. Wish DT offered an option like this which would most likely be way more elegant.

 

[costalcat]

@Daskoff This is great . Let us know how it goes on the highway and with the trailer. My wife was not crazy about the last trip we had pulling a trailer with this exhaust. Seems the drone was loudest right at the speed/rpms that were perfect for towing....

 

[Daskoff]

@Daskoff This is great . Let us know how it goes on the highway and with the trailer. My wife was not crazy about the last trip we had pulling a trailer with this exhaust. Seems the drone was loudest right at the speed/rpms that were perfect for towing....

Based on my calcs - a speed of 2,500 rpm would require a 20" tube and as you drop RPMs by 100 you increase the tube length by roughly 1" so because I was targeting 2,000 RPM I needed a 25" pipe. The interior DBs measured on my iPhone app with windows closed and driving around town (idle to 2,500 rpm) was between 40-50 db - (idle was about 30 db) depending how aggressive you push the skinny pedal. Unfortunately I did not take measurements before the pipe install.

Once I get going with the trailer I'll take more measurements. My rpms for 65-70 mPH is between 2,500-3,000 but not sure I will be going that fast with a trailer. I also have 285 BFG Ko2 on 16" wheels so my speedo is off a bit to further complicate things.

 

[costalcat]

Based on my calcs - a speed of 2,500 rpm would require a 20" tube and as you drop RPMs by 100 you increase the tube length by roughly 1" so because I was targeting 2,000 RPM I needed a 25" pipe. The interior DBs measured on my iPhone app with windows closed and driving around town (idle to 2,500 rpm) was between 40-50 db - (idle was about 30 db) depending how aggressive you push the skinny pedal. Unfortunately I did not take measurements before the pipe install.

Once I get going with the trailer I'll take more measurements. My rpms for 65-70 mPH is between 2,500-3,000 but not sure I will be going that fast with a trailer. I also have 285 BFG Ko2 on 16" wheels so my speedo is off a bit to further complicate things.

Thanks again! I have the same tires but in 18's. pulling my 24ft travel trailer 60 - 63 seemed to be the right place for me...

 

[cmck]

I had this drone as described in the op. I was able to drop out much of it by putting dynamat extreme in the doors, rear quarters and fender wells. I was flipping out the tired factory head unit and speakers at the time. The reduced drone was a really nice bonus.

 

[maxse01]

I've got the DT headers, custom mid pips and flowmaster hi flow cats, and the DT catback. My truck is loud, but I don't think it's annoying. You hear it on the highway for sure, but it's more of a mellow tone than a drone. I will post up a revving vid and then take a highway cruising vid in a day or two.

Like others have said, get the headers. Mine was a little drony when I just had the catback. Once the headers went in the whole system calmed down and mellowed out.

 

[maxse01]

So much power it knocked my phone over

 

[landylover21]

I have a bunch of exhaust comparison vids and test drives in my gallery, just an FYI.

 

[krice118]

@maxse01
If you don't mind me asking, how much was your exhaust minus the headers?

 

[maxse01]

The DT Catback was $550 shipped, then I spent about $500 getting the custom work done on the mid section. They're 2.5 inch pipes with flomaster hi flow cats and o2 spacers. No CEL, and it runs great. Much more noticeable low end power. Where it would have previously had to grab 4th on the highway for passing, it will just stay in 5th and accelerate. I'm very happy with the power gains of the entire system, I would estimate that I made up for the 33's and all the armor I've added. It feels just as quick as my wife's stock 100, but sounds MUCH better.

If you want some more clips I can get them for you. 1 thing I will admit, it is somewhat drony on the highway at slow speed (under 2,000rpms). If you're going faster than that it's ok, but you still know it's there. I might have a resonator put in somewhere at some point to take the edge off a little bit.

 

[abuck99]

So much power it knocked my phone over

Max- It sounds great, but guess Im getting too old- cause thats too loud for me. Thanks for posting the clip, confirms that set up is not stealthy enough for my taste.