Backstory: originally purchased a Yonaka catback (2.5" mandrel bent stainless, dual resonators, straight through standard muffler), but it was too loud. VERY bassy, drony, and a bit farty. Loud even off idle while driving like a granny. Unlivable and a cop magnet. So I did a little research and found Dynomax's Super Turbos were hailed as the best combo for good flow while maintaining low noise. Bang for the buck was a bonus. So, I hacked off the Yonaka's muffler in hopes of finding a quieter yet pleasing non-stock sound. Note that from the cat to the engine is still completely stock.

Dynomax 14" (17733): A good improvement. The deepness was reduced noticeably, to the point that it won't set off car alarms, but still completely aftermarket sounding. Fartiness dropped by I'd say 66%. Could still be a bit annoying with what's left over, but only when you're flooring it in the mid RPMs. But drone? Still there. Very rumbly inside and outside the car at cold idle, and just a barrier of bass inside at freeway speeds. For up to 50mph, it was passable, but beyond that was rough, especially with the windows closed. Even reverberated back at me in underpasses and tunnels. Next!

Dynomax 20" "Hemi" (17748): WAAAAAY better. THIS is close to the sound I was looking for! Drone is 90% gone. There's just enough sound left on the freeway to remind you you're not driving a stock car, without weird looks from passers by, or the pounding head after your trip. Same with around town driving, where constant throttle is pretty quiet, and the muffler comes to life in a respectable fashion when you get on it. You can also hear the separation of exhaust pulses a bit, vs the continuous deep hum of the other mufflers. Idle, cold and warm, is around 50% quieter, still a bit deep, but definitely won't annoy the neighbors. And fartiness has turned into a mild nasally growl vs a can of angry bees. A keeper, as I can't fit anything longer back there (already had to hack up the axle back piping a little to make room), and anything else will introduce more restriction (chambered/baffled) or noise (straight through/weird internal designs). If anything, I'd compare the sound level overall to what louder factory exhausts sound like on normal modern cars (ie. not Lambos and Porsches).

This would also be a great mod for anyone looking for a little extra sound out of their stock exhaust without breaking the bank (17747 for 20" @ 2.25", 17736 for 14" @ 2"; smallest diameters available), or to replace a muffler that fell off (my original problem). The stock muffler is VERY VERY restrictive, and I felt an immediate boost in power when mine fell off (dragged it scraping from a busy freeway toll booth to the first parking lot 1mi away! ). After I installed the full exhaust, and also with the 14" Dynomax, I saw a consistent 2mph gain, despite me being heavy on the gas (130hp = flooring it to keep up with traffic... ). Changing mufflers should get you at least halfway there.



EDIT: Added images of my hackjob install. Welder coming Soon™.

 

Thanks for the feedback. I've considered a small exhaust change, but I don't want drone or anything else, just a little noise. This was great. that 20 does look pretty big.

Has anyone every dynoed an Accord to see gains of exhausts? I didn't think there was much of a gain, but I'd be curious.

 

Yup, the 20 is very long. The longest single in/out turbo muffler Dynomax makes. Going by RockAuto's sizing for the stock muffler, the 20" is 4" longer than stock, along with 0.75" wider, though 2.75" thinner. So internally it's still a smaller volume than stock. The benefit over stock is from using a more free-flowing design, which improves flow and increases noise. It's quiet enough that I want to go out for a drive just to hear the exhaust, without the worry of attracting the attention of cops!

Not sure about dynos, but the feel of the increased flow helped a lot on the way home, after I put what was left of my old muffler in the trunk. I didn't expect anything to change, since the rest of the system was still tiny 1.75" crush bent piping from the factory.

 

Pics added to original post.

 

Stock single cam really isn't going to see much with just an exhaust. If you have a B2 or other F series that has the OEM 4-1 exhaust manifold, switching to a 4-2-1 header design, test pipe and at least a 2 3/8" full exhaust might show a few HP in the top end. Mostly it's just gonna be noise.

H series is a different story. They pick up quite a bit with a header that has a 2.5" collector and a full 3" exhaust.

 

Good notes! I have been muffler hunting for something OEMish but not so restrictive. I knew the small super turbo muffler would not be good enough. I didn't know they made a longer one. That seems about perfect. Although I would opt for twin tips just to keep it classy.

$56 on amazon isn't too shabby either. I'm debating this or putting on an OEM muffler from a newer accord (I have an 05 as well).

 

The muffler has become a bit louder after 500mi, but nowhere near as loud as the smaller version. A bit more rumbly cruising past 2000RPM, where it was nearly silent before.

I would have gone twin tip, but there wasn't enough room for it. The single tip I have is already very short, and goes back nearly to the body of the muffler just to keep it from sticking out too much. Whenever I get a welder, I can make more room to fit something less cheesy than a bolt on tip.

If there's enough room and the inlet/outlet are aligned properly, you can give the newer Accord muffler a try. I looked for OEM mufflers to use on my car, too (via RockAuto) but there wasn't anything at 2.5" that would line up and be small enough.

 

Do you have a video so we can hear it? Maybe a driveby as well to hear it at speed.

 

Don't have anyone that will stand on the side of the road with a camera, but I can get some in-car video with the windows down. Been wanting to get a video before they straighten out a local curvy road that's been around forever (nearing construction time).

 

You don't need a person, just put your phone on the side of the road and drive by, the muffler is down low anyway and it will get picked up.

Just don't run over the phone.