Technical Exhaust Drone/Resonance

Haven't tried it, but years ago I was told by someone who did, that a stainless hose clamp around the pipes will suppress drone.

 

Back years ago when I lived in Texas I had a buddy with a 383 Mopar that he had turbos and turn downs in front of the rear axle that rode with one time for a 40 mile jaunt from McGregor to Little River for the drags and that was the first and last time I ever rode in that car. The drone gave me a three day headache.

 

This works! I have a full exhaust all the way out the back with flow masters it had drone so bad at cruising speed I couldn't stand to drive it. I tried h pipes, x pipes and they didn't change anything. I added the Helmholtz style pipes to it and all the drone is completely gone.

 

When I got my 49 Buick on the road with the 472 Cad engine it was just a little too loud and did have a drone to it. I added resonators right after the mufflers and that fixed it. Now it is a pleasure to drive.

 

You might try a set of "J" pipes. The guy at the muffler shop I go to had never heard of them. He couldn't believe what a difference they made in the exhaust sound after he got them installed..... Exhaust still sounds good, just no drone.

There is a chart below the picture to calculate the length you need.

It is just a pipe shaped like a "J", installed just behind the muffler. It is capped at the end and the frequency bounces back and cancels itself out. You can't just make them any length and expect them to work. I recommend doing some reading on them. I think mine are 23.5 inches long.....


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Kind of made me laugh thinking about it but in hi-school (early 70's) I had an El-camino with a big block & had the great idea to put Cyclone Purple Hornies on it. They dumped out under the floorboards in front of the seat. That thing droned & vibrated so bad even I at 16 years old couldn't stand it. My dad told me if I didn't get rid of them, he would for me. Good memories!

 

Helmholtz resonator = "J pipe".

Works for sure. Like little red 50, I couldn't tolerate my newly completed car. The drone was brain melting, genuinely sickening, not just unpleasant or annoying. Car is pretty much perfect now.

Chris

 

old information...
Hello,

Ever since my brother purchased the fast 58 Impala new, exhausts were always the clue to go faster at the drags. We could not install custom equal length header pipes as they were not stock. Our local muffler/welding guy said he could design a system that would flow straight through from the heads to past the rear axle for the best performance.

The flow would be under the car through a set of tubular mufflers and out of the back. But, all cars were inspected and the individual pipe headers would give a clue as to not being cast iron and stock. So, that was ok for later.

The complete set was gathered by our local muffler/welding owner and we started with the first small pipe units on hand, not the whole kit.

So, we worked with what we had. Nothing in the rules had options for shortening the exhaust pipes from the rear bumper. Now, a lot of racers started to modify their exhausts to get some advantage over the other matching motor combos. The tubular corvette mufflers by themselves made the sound as if there were no mufflers at all. We had short curved down facing tubular ends that were directly under the cab seating area.

Both of them were individual cases, but the standard warnings were given to us by the owner. What warnings? Well for the major one, exhausts at the front of the rear wheel always draws exhaust smoke and unseen CO into the car. Whether it is through and open window or a leaky seal. It will come in and no one will be able to tell it. “it’s a little smoke, but ok…”

Then, as the local muffler guy was working to put together all of his custom components ready for the custom installation on the Impala, we tried to extend the pipes back to just behind the tires.

The next area is behind the tire. It is the same result or a little less due to the spinning tire moving the smoke or bad fumes away. But, our experiments always drew them in to the cab. We can’t smell CO, but if a gas smell or exhaust smell it felt, then the CO is there. Otherwise, the CO is there and we are all dizzy. Dizzy from fumes, seen or not... No, not that kind of smoke...!

Jnaki

Luckily, we only had to endure several weeks worth of loud exhausts in the 58 Impala. But, we did find a rev point that made the motor/exhaust mellow and almost as quiet as stock. When we stopped at a street light area, if in traffic, we raised the RPMs up to that fairly quiet level.

So, start by checking where your final exhaust pipe exit is located and if there are any cracks or splits from s****ing. We can attest that despite the exhaust tips behind the tire opening (Looks great, but worse for smell, the shorty tips, still drew in the exhaust smell, even when running on a hot summer night with all of the windows down) were tried and tested.)


But, when our muffler guy finished the custom made pipe routing system, it was the best and still gave us performance we wanted when necessary. The cruising noise was almost non existent, other than the rumble of the big modified 348 motor.

The final system was put together and still utilized the custom down tube outlet. The Corvette Mufflers and the rest of the routing was simple enough for our local welder. We still had the “under car” scavenger pipes in the backyard garage attic rafters, as they were also illegal for the daily street driving. Allowable for a short time at the drags in our cl***, but the protest kept the straight pipes off of the racing cars in the cl***es.

Note:

The only good thing that came from this exhaust outlet/scavenger pipe history was the design and development of a cool way to open and close the outlet cap.

The down tube end caps would have a slit cut into one of the nut/bolt holes. The nut was now permanently attached to the cap with a wingnut. When the wingnuts were loosened, the cap easily slid out and over to open the exhaust opening. The wing nut was easier to tighten and keep in place. Even a small rock could tighten the wing… So, it was a miracle, but my brother put me in charge of the modification and it worked well as planned.

Before we started using blue Loc-***e, several of the wing nuts came loose and fell off, creating a jiggling metal on metal sound. The cap was loose and one remaining wing nut was keeping the whole thing from falling completely off. But, a spot weld on the end of the bolt took care of lost wingnuts. So, if and when we got stopped (never did) after a high speed open exhaust run on Cherry Avenue or anywhere, several seconds was all it took to cap up the outlets. Fast and easy. YRMV
A short bend tubing, from the mufflers exiting in front of the wheel. Not good as it was loud and the aroma came right through the floorboard.
The next ones we were offered at the muffler shop were the "above the rear axle" and out to the side, in back of the rear wheel. Now, it was definitely quieter, but we could still hear the sound all of the time. The sound was pretty good as we drove down the street and anytime we drove into the drive-in restaurant parking lots, it was definitely a “head turner.” But again, it was loud all of the time and we still could get fumes when all of the windows were down, especially during the summer time cruises. So, one last choice was offered to us.

Impressive and legal at the drags in the Stock car cl***. All open outlets had to be closed, so the shorter pipes behind the wheel supposedly gave us an advantage. YRMV

With the Corvette mufflers and rear exit pipes, 14.68was the quickest E.T. but, I had on the real Bruce Slicks for traction off of the line…) The Corvette Mufflers qualified in the stock cl*** due to it being on the Chevy dealer’s parts list and anyone could buy them stock. (no actual header pipe systems were allowed)
Then came the last added custom wheels...
thanks, @themoose

 

Put bend of around 30 to 45 degrees in the system and the drone will be gone. I had late model mustang gt mufflers before the axle on my 32. I made one trip and removed them. Some time later I asked on another forum for advice. One of the members had diesel pickup exp. he told me about the bend. I put the gt mufflers back on with some short tall pipes with a 45 degree bend in them that exited after the rear wheels. Worked better than I could have imagined. I'm sure some mufflers won't respond but everyone that I have done since have. Good luck with your search.

 

If you don't want drone, you will have to change your mufflers. That is the only correct way. A j pipe can work but will only take the drone away at a certain rim.