Hey guys, I have duals on my 74 Buick and around 55-65 it has the dreaded "drone" noise. Once you reach 70 and above or 50 and below it goes away. Will an H pipe help this? Currently i have Xcelerator mufflers with no H pipe. Just wondering whatto do to get rid of the drone. Thanks for any help
The drone is caused by the exhaust system being "excited" by exhaust pulses at its natural harmonic frequency. I would probably start by adding a pair of large diameter (same as your tailpipes or even 1/4" larger), 12" to 18" long glasspacks as resonators, as far back in the system as possible. Adding the resonators changes the resonance frequency and usually eliminates drone issues. If you use traditional glass packs, install them with the smooth ramp side of the louvers facing forward; the "open" side of the louvers should be facing the tailpipe outlets. With or without the added resonators, an X or H pipe should help quite a bit. Adding the balance tube (H or X pipe) also changes the resonance frequency and balances the pulses between the left and right sides by providing a coupling between the two sides. If you are looking for every possible bit of power, use an X pipe instead of an H pipe; the X pipe usually results in a couple of percent higher higher peak torque than an H pipe. Just my $.02.
My mufflers are right at the rear axle, just in front of it. So if I add glasspacks how far in front of the mufflers should I go. And how much quieter will the exhaust be? I like the sound of it, just kinda irratating at around 55-65. I have a full 2.5 inch system front to back, it dumps down at a 45 degree angle at the back of the car. Thanks for the advise
Don't put the glasspacks in front of the mufflers; put them as far back in the tailpipes as possible. Best place is to tuck them up in the quarter panels, behind the axle and just in front of your tailpipe outlets. If you use glasspacks with an ID the same diameter or slightly larger than your existing tailpipe, it won't really make the exhaust much quieter, but it might smooth it out a little. It should shift the resonant frequency enough that you won't hear the drone at normal cruising speeds.
No room after the mufflers behind the axle. I am gonna try the H pipe, if that don't do it I will change mufflers. Thanks
the exhaust system being "excited" Same thing happens to me when I hear a nice set of glass packs! What should I do?
LOL, I love the sound of glass pacs, but I am getting older and I plan on cruising alot this summer and I don't want that sound anymore
Definitely go with the X cross over. Better noise reduction, better scavenging, and hence, slightly better fuel economy. It will also balance the back flow should anything damage a muffler or pipe on one side so you don't burn out valves. A few years back, "HOT ROF" magazine did a thorough test of exhaust options, from none, to open, right through the X cross over. The straight, not balanced system was tied with no exhaust for last place. Needless to say, they did not test a single system at all. H was an improvement, and X won by a healthy margin, both for horse power and mileage. There is not up charge to an X over an H, either.
It is hard to believe but I put some Headman resonator tips on mine and it made a big difference as far as the drone went.
I ordered my H pipe today, I am also going to change my mufflers to something different I am just not happy with the sound. The guy does great work, but I just don't like the mufflers. So, time to start listening to different mufflers to see what I want
