New Exhaust System

28” helmholtz will knock out 1800 RPM drone. 25-26” is good for ~1950-2050 rpm.

 

I’m kicking that around. There’s room to install those but my fab skills to do it are questionable.

 

Thanks. Thought there was a difference for 2.5 inch vs 3 inch pipe.

 

In an open-ended system like a subwoofer vent, it's the volume of air that interacts with the box/driver and resonants, so port diameter is important and is factored in to the resonance. A smaller diameter vent would require a shorter length compared to a larger diameter vent.

In a helmholtz resonator that is closed on one end, the distance from the opening of the pipe to the closed end is what's important; it creates a mechanical time delay as the sound wave starts at the open end, travels to the closed end, then travels back to to the open end. If that distance is 1/4 of the wavelength of the frequency you are targeting, then it creates destructive interference since it travels 1/4 of the wavelength down, and another 1/4 wavelength back to arrive back in the system 1/2 wavelength different, or with opposing peaks and valleys. That's what cancels the drone/sound. Think about wiring two subwoofers backwards from each other: while one cone moves out, the other cone moves in and you net exactly zero bass. Doesn't matter the size of the woofer if they are wired backwards they will still cancel each other out; tube diameter only determines HOW much is cancelled out, with diminishing returns. So you can cheat and use a smaller diameter tube than the main system with good results.

 

Is SPD running a Black Friday sale yet? I keep waffling back and forth on the downpipes. I've pulled a trailer almost 3k miles in the last month and don't want too much racket... but mo' powahhhh!!

 

Buy the exhaust. You’ll be happy with it. I was and still am. I’m just bored and tinkering because I can. I’ve had zero complaints from my family or friends about the noise while daily driving or towing. I’ve had zero negatives towing the rzr with this exhaust nor driving around town. It’s just a rowdy dumped exhaust. If you’ve had one you’ve had this.

I’m debating painting my new tips with flat bbq paint just to ensure I get max torque and flow.

 

That's my hold up - a rowdy dumped exhaust is a little too rowdy for me. My current exhaust isn't exactly boisterous, but it can be somewhat vociferous at times. I've driven my truck around kinda straight piped for a day and it wasn't for me...

I also don't usually tow anything as small as a razor. I often do two or three hours on the highway 70 MPH with a few thousand feet elevation gain sometimes. Done and too much noise can be fatiguing.

 

I understand the way it works. I thought another exhaust maker stated 2 separate charts for a a 2.5 inch system and a 3 inch. Although I only had the 2.5 inch one.
Thanks again...

 

I apologize if I spoke to you as if on my high-horse. That wasn't the intention, but sometimes my filters glitch a little and words vomit forth.. If they did post a chart, I'd be interested to see it. I have not seen one in all of my research but that doesn't mean I'm opposed to learning more about it.

 

I did transpose my column for the rpm's and length so appreciatemy bad info. I didn't take it any other way than more information out there how it cancels the drone. It's all good.

 

The downpipes do ratchet up the sound a lot with the same catback under higher loads. It took my catback from mild to wild under heavy throttle. It didn't annoy me on the towing trip I just had, but I’m still in the phase where I’m totally entertained by it. I also have side exit duals so with the windows up it’s not too bad, but with the windows down driving through town it’s pretty loud. It will definitely draw some attention. Idling and low throttle driving though it is not much louder than just the catback.

I am curious about those valvetronic mufflers with a valve that either goes to straight through with almost no noise cancelling, or through a chambered portion of the muffler that may even be quieter than stock. Could be perfect with a set of the midpipes. You can have either option at the push of a button.

 

Dynomax used to have a muffler with a butterfly valve that did a similar thing. The more throttle, the more the valve opened and let the eagles fly. If I recall correctly, you could adjust the tension but complaints of it rattling or getting stuck open/closed ran rampant on the Dodge forums. This was years ago so not sure if they still make it. The valvetronic mufflers sound ideal especially the video I saw a while back where they installed a set on a Mustang and connected it to ODB2 so it was synced with throttle position.

 

Spoke to Keith yesterday and sent him pics of the pipe dump over the axle along with measurements. He is fabbing up a couple resonators for this particular exhaust similar to what he has available on his site:


They will mount on the downhill slopes of both tailpipes and aim in the direction of the driver side. Will update with more info once they arrive and I get them installed. He estimates a 20-50% drone reduction.

 

I dumped mine I put the hemholtz before the muffler. When I spoke with him he said he gets a lot better reduction after the muffler.

 

Yep, and since there really isn't much pipe coming out of the muffler on this system, the best position for them is coming down from the highest point of the bend over the axle (per Keith). He even had Terry, his shop guru, in the background of the phone call discussing placement.

 

That's about the only place you can put them and clear the spare tire when they are positioned 90deg to the direction the tailpipes are running. On the uphill portion, youd have potential interference with the driveline or fuel tank.

I figured if drone was bad on my system, I'd tap into the uphill portion but run them forward the front parallel to the rest of the system using some elbows, similar to Magnaflow or TWC solutions.

 

I’d be interested in a set. I took the tips off I made today and think I’ll leave them off unless I tow. Above 2000 they are fine and the noise is gone but the drone below 2000 was just annoyingly loud. The dumped exhaust is way tamer in that it’s not a drone it’s just the exhaust note.

 

Initially, he was planning to put them there (on the incline). I don't have a spare tire mounted on the underside so I have plenty of room in the aforementioned placement. The resonator going on the passenger side pipe will have a "T" mount with the resonator bending 90 deg toward the driver side. It'll look pretty funky but no one will be able to really see it.

 

What tips did you have?

 

He'd need to know the angle of the incline though.

 

He's built many systems like this before so he understands the design. The first idea he was bouncing around looked like your picture, but it got scrapped for the post-bend placement.

 

He originally, back a few years, had them placed right after the muffler bending back over the top but you get better drone reduction placed where he stated.

 

You could run this with a helmz in the x-pipe like they do for other kits. And the direction doesn’t matter. We’ll be doing a straight pipe opposite direction on the old man’s exhaust

 

That looks badass too.

I believe 26-28" length is needed to kill drone at 1800ish RPM

 

honestly 3" with carven TRs are great. i dont mind hearing a bit of exhaust though neither beside i also have the stereo
just ran out about 30min away yesterday and was running 70-80mph and its was actually pretty quiet

 

I tried this way but didn't kill all the drone. Will follow Keith's advice to put it aft of the mufflers. Know it's not SPD but kill that drone...

 

Just some I built out of 3”.

 

I love the way this sounds. Just like to experiment and tinker. Sometimes it’s a win and sometimes it’s not.

 

There so many quality exhaust shops in Conroe and Houston that can weld that up.