A silent room is deafening to me, the squeal in both ears becomes overwhelming. It changes volume when I’m dehydrated, exposed to certain volumes or sounds. It overpowers frequencies in the high ranges so hearing tests show I can’t hear them at all. When I wear earplugs to avoid further hearing loss like when in the convertibles or on the motorcycle or at concerts, the plugs mask the outside but brings the tinnitus to the forefront. There are apps that let you play a sound at the frequency of your tinnitus and when you stop the tinnitus seems lower. Anyway, back to the car. I have been doing all this testing and revision with the top up. Because it’s been cold and also the pump seized. I’ve got a new one waiting to be installed. If I tune the exhaust to a comfortable level with the top up, it’ll be interesting to hear what it sounds like with the top down. My butt dyno is the only thing I’ll have to go by. But I’m sure it’ll be better that it was with the old exhaust.
I bought a couple of 90° elbows so I can try to move the q-wave pipes. I’m contemplating moving them to the outlets of the mufflers between the muffler and the tailpipe before it heads over the rear end. If I put the tees there, maybe I can put the j-pipes (that’s the way they’re shaped in most installs) along the outsides of each muffler. I don’t really mind how they look where they are but I think now that I’ve seen they can have an impact I’m going to reconfigure the exhaust yet again. Which is fine. I’m a pro at it now. Besides, I’ve got to weld a bung for the O2 sensor on the drivers side downpipe. The clamped on one leaks a little and that throws off the readings and the tuning.
I’ve changed the length of the q-wave tubes 3 times. They’re made of a few segments with slip fit and band clamps so I can tune them. Each time I adjust the length the drone goes away at one RPM range and appears at another. The math takes into account the temperature because that changes the speed of sound, and I’ve noticed there’s less drone when the engine is cool. Probably why I pull out of the driveway and think “yay! I did it” and then as I drive and the engine warms up the drone gets louder. I need to look at the math again, and which temp I need to measure and how so I plug that into the formula. I think being just ahead of the exits is a factor so I’m gonna wait to get the elbows on hand and see if I can move these up behind the muffler.
You should mount it up before spending so much time testing. The mounts could radically change the about of vibration transferred into the car.
I have always suspected that the closer you can put the trombones to the collectors the more effective they will be but it would be handy to know if your testing agrees or not. Both the loudness and the range might be effected. If you would, let us know your length from the end to the T. Jim
I’ve been fortunate that my hearing hasn’t been affected by my line of work. Until solid state controls replaced most of the relays and drives replaced generators elevator motor rooms were very noisy places. Many of the people I’ve worked with over the years have issues.
Hi Jim, from the capped end to the tee fitting the pipes are now 29.5” long. I’ve tested them out at 31.5 and 33.5 and each time they addressed a different frequency, which makes sense since the length does determine the size of the wave that bounces back. I set my idle at 1800 via the EFI so I could get out and listen near the exhaust pipe. The sound coming out of the exits had no “note”, but when I crouched down and listened under the bumper the “note” was there droning away. Something tells me these q-wave pipes will be more effective if I can get them in before the tailpipes, since those things are amplifying the resonance.
I agree. I had been testing things prior to mounting them solidly and with the car off the ground and then the real-world, mounted and out on the street would be way different. I’m also learning that how warmed up the car is changes things too. The speed of sound changes with temperature, and I hadn’t known that so hadn’t taken into account what is needed to compensate. No wonder the car would get louder as it warmed up. Duh.
I wonder if, in an ideal world, you'd be able to design an active system using stepper motors or butterflys that would change lengths in real time based on rpm, temperature etc! I'm almost scared to suggest this because I feel like you of all the people here might be crazy enough to try it
“…might be…”? You underestimate me. But since you mentioned it, I could probably tie something into the Holley Sniper EFI since it has some output capabilities. And I have ideas for the variable tuning mechanism. I could probably work a vacuum servo in there somewhere. Or a hydraulic actuator. But I’m not going to try it. It’s been done in one form or another. OEM and aftermarket. For tuning sound and volume. my other car has an aftermarket variable exhaust system that has two paths with two exhaust tips for gasses.. one muffled, the other straight through. The straight through has a vacuum solenoid and butterfly, and I can select how much or how little throttle I need to give it to open the straight through pipe.
I could be wrong but I think the guys trying this were successful using a length of about 15". It's possible your 30" pipes could be half wave instead of quarter wave which wouldn't be nearly as effective. Bear in mind a header primary tube is designed to be a full wave tube at operating frequency and they are usually 32-36" long. (The length is tuned to let the exhaust pulse reach the end just as the next pulse enters the tube so that the suction created by the first pulse pulls the second pulse out of the port, this is why shortie headers are not nearly as effective.) Of course the operating range is usually going to be somewhere around the torque peak and maybe higher. So if your drone is at half that you'd double that length then quarter it for Q-wave which makes 15" sound just about right. As for the location, you can put it anywhere you want to but the pulses will be strongest at the end of the headers I think so if you cancel them there it will be most effective. The muffler smooths out the pulses making them longer and harder to cancel. One theory is that you should locate them at the hot spot in the pipe which you can find with an IR gun. So far nobody has proven that that is better though. Jim
Thanks Jim. 15” is not a number I came up with while trying a few “calculators” I found. But I also hadn’t heard that the downpipes are tuned in any way. Not sure these TA pipes are. Today I took those resonator tubes off the back and drove around. The drone was really loud and worst at 118-120hz. So I went back home and figured out based on the calculations that the jpipes need to be 29.5” long. Which is almost 30, so if I am miscalculating and making half-wave pipes when I need quarter wave, then 15 would be right. The 90° elbows arrived today. I took out the bullet resonators up front, disconnected everything, and now the drivers side has: the downpipe to the mid pipe to the tee with a 29.5” right angle branch that heads toward the frame and then turns to the front, then the muffler and tailpipe with 45° elbows pointing out to the side. I only did one side today. I’ll do the other side when I can, and if it doesn’t cancel the 118-120hz then I’ll try a 15” pipe and see what happens. Can’t hurt.
I dunno. When I was a kid having dual exhaust was something special. Now pretty much anything can have two tailpipes. Maybe they go 4 into 1 into 2, but I guess to my mind it this car should have duals. back when I was shopping exhausts I checked with Gardner who makes a repro stock exhaust. It seemed pricey and there was a several month wait to get a system. I’m probably over the cost and time that would have been. Also in more pain than I needed to be. But whatever.
With the stock iron manifolds there isn't much tuning going on in the stock system but even there they evidently did tune it for a quiet ride and average performance and mileage. Overall it was a good system that benefited from less restrictive mufflers and of course, headers. Speaking of which, there is a great deal of variation in headers and much of it isn't good, but it's hard to go wrong if the primary tubes are actually equal length within say about 2" and the diameter is reasonable. As for the down tube, or header tube, whatever you want to call it but the first large tube that dumps into the muffler, I haven't bothered to check but evidently those do develop hot spots (at least when connected to headers) at specific locations. Whether more than one and how much they move depending on RPM I couldn't say. The one guy I know who looked into that seemed to think putting the traps pretty much any place in that tube was about the same but I don't know that he did much experimenting. He didn't use the hot spot location but he was very happy with the results. Jim
PROGRESS! Today I put the second j-pipe on. L-pipes, really. But anyway… The drone frequency I was targeting with the 29.5” pipes is much lower. The pipes are tee’d in ahead of the muffler, head outward toward the frame, then make a 90°turn toward the front of the car along the frame. I took a drive, let the car warm up this time before I got my hopes up, and waited for the drone. There was some at part throttle, maybe 1400-1600 rpm but not nearly as loud as it had been, I think it’s just exhaust sound, not drone, and maybe some resonance because the hangers in the rear are too rigid. When it hit the droning RPM around 1800, there was just a little bit of the sound I was targeting. I need to put some good tips on the tailpipes after I address the stiff hanger issue. I had some 45° elbows on there but I’m gonna put some that go under the bumper and straight out. I also want to add some supports for the pipes I added. The reduced drone lets me hear other things. That fuel tank is very resonant like a drum so I also want to drop the fuel tank a little and slip a pad between it and the underside of the trunk floor. Theres supposed to be one but it didn’t come with the new tank. So I’ve gotten somewhere! And there are only the two dynomax mufflers and the pipes I made. No resonators. Supposed to be a bit warmer this weekend so I’ll do some more tweaking.
For now, my not-to-scale napkin sketch… A friend said “16 band clamps, seems too complicated, too many places it can leak and rattle”. I get it, but I’ve got to get it tuned first so no welding.
