Solution for B&B Exhaust Drone?

[ZBrink]

My new-to-me 1990 has the old style Billy Boat exhaust and the drone is absolutely unbearable for me at all cruising speeds in 6th gear (1700-2400 RPM). It currently has OEM manifolds but I plan to install Maximizer/OBX headers with either 200 or 400 cell cats.

I've learned of several ideas/concepts that have worked for other vehicles with different exhaust systems, more space etc:

1) Welding in a j-pipe or Helmholtz resonator before the mufflers; loads of videos on YouTube if you're not familiar (it's works but I'm not sure there is enough space under the vehicle for this)
2) Adding mass/weight to the exterior of the mufflers (maybe the engineers of the forum can better explain this)
3) Wrapping the mufflers in header/exhaust wrap (would this last long terms?)

This is somewhat of a budget build/restoration for me and I'm trying to do the majority of work myself with the help of WAZOO and other members. Does anyone know of any other realistic and sustainable solutions or care to comment with their knowledge on the ones I've listed above?

EDIT: Cost is a factor as the previous owner misrepresented its condition and the maintenance/repairs/restoration is starting to nickel and dime me. The previous owner powder coated the exhaust tips black to match the wheels which he also had powder coated black. If I get any different exhaust, new or used, I would also have to powder coat the tips to match the wheels.

[Mikey]

Do not wrap exhaust. It will only lead to corrosion.
Do you have an x-pipe in the center just aft of the transmission?

[WARP TEN]

A good solution would be to get a Corsa exhaust, and if budget constrained, you might be able to find a used one. Marc Haibeck might have one, as might others on this forum. The resonance frequencies created by the LT5 and many other engines occurs primarily at two rpm points, about 1800 and about 3400, and they manifest themselves most noticeably under light throttle application. The Corsa system (like the stock system) utilizes Helmholtz resonators to tame them both. There is one in the center resonator that deals with one of the rpm points and there are Helmholtz resonators in each of the rear mufflers to tame the other. (I forget which handles which frequency). In the early days the Corsa was the only one to really quiet resonance other than the stock system. Today I believe there are other systems that do a fairly good job of it but not sure which. Others on the forum will undoubtedly chime in. Good luck with it. But I think getting a different exhaust system than the one you have is probably the most straightforward approach. --Bob

[Karl]

Either upgrade to their new system or try this. I deleted my resonator and installed an x pipe but have not done the NPP mod.

https://www.zr1.net/forum/showthread.php?t=22512

[Raykahn]

I'll err on the side of Warp Ten here and say you may be better off planning to get a new catback system that is designed more towards eliminating drone.

OBX/Maximizer has a catback system that is very reasonably priced on Walmart to match the headers you bought. From what I have read here on the forums and seen on youtube it has little or no drone.

Originally Posted by ZBrink

2) Adding mass/weight to the exterior of the mufflers (maybe the engineers of the forum can better explain this)

Warp Ten alluded to this by mentioning resonant frequency. There will be vibration frequencies that make the mufflers give off excess noise. If you have ever turned a stereo up in a car and had the door start rattling, its the exact same thing. Its a combination of material type, thickness, surface area, and vibration frequency.

By adding mass to the large surface areas you change the amount of energy required to hit that resonant frequency. That can reduce or eliminate it through the vibration ranges it will see use at. In sound deadening (for car stereo example) this is done by adhering sheets of butyl to the sheet metal panels to change the overall mass. You probably couldn't use the same stuff for the muffler because of the more extreme heat.

Applying exhaust wrap to the muffler would achieve a similar effect, it is adding mass. Another option would be welding extra material to the muffler to reduce the size of the resonant zones and/or add mass.

Originally Posted by ZBrink

3) Wrapping the mufflers in header/exhaust wrap (would this last long terms?)

I think as long as you understand why the exhaust wrap could lead to corrosion and how to mitigate that, its an option.

The danger of exhaust wrap comes from it getting wet, and then holding that moisture against your system for a long period of time. Aside from the obvious things, like rain or puddles, moisture can also come from not allowing the headers/exhaust to get hot enough to force evaporation. There is moisture in the air, and some heat can cause that to condense inside the wraps. So very short errand runs can actually be bad if there isn't a longer drive to break those up.

The risk here can easily be overblown. If it gets wet, at first opportunity take the car for a longer drive to build enough heat throughout your exhaust system and force any moisture to evaporate. Starting the car and letting it idle won't be enough to do this, the engine needs proper load to build the correct amount of heat, and enough time for all the moisture to be forced out.

So consider your usage. Is it a daily driver? That might be a little higher risk if you expect to be driving it in the rain. Weekend cruiser? No problem, that is low risk.

[Mikey]

I wish it was that simple Raykahn but I ignored the warnings on header wrap on an LT1 powered 383ci 94C4 and they rotted through in a year just as others had predicted. Car rarely saw any rain and all drives were long enough to reach full operating temperature. Lived in Detroit metro at the time, nothing was less than half hour. Car was never exposed to winter or salt either. Of course SE Michigan is humid.

[XfireZ51]

Just a long term update. Last year the DynoMax muffs had pretty much become a boom chamber. We opened one up and the insulation was totally carbonized. This time I decided to go w MagnaFlow muff w almost identical dimensions. Al moved the NPP valves over to these new mufflers and we made one small but I think important change whichis to extend the tips beyond the rear valence panel by ~ .75?. The MagnaFlows are of better construction than the Dyno and w valves closed u get a much mellower exhaust note. Valves open is significantly louder but even then more tolerable than the DynoMax.
I am thinking of trying this next. My gf has pretty sensitive hearing. Anyone have a comment on Block It?

https://www.tkoperformance.com/84-96...nds_p_710.html

[ZBrink]

Originally Posted by Karl

Either upgrade to their new system or try this. I deleted my resonator and installed an x pipe but have not done the NPP mod.

https://www.zr1.net/forum/showthread.php?t=22512

Hi, I'm a little confused. Do you have the old style B&B system? Are you saying that you had drone but switching to an x-pipe resolved the drone? Upgrading to their new system is not in the fiscal cards at this time. EDIT: I double checked and I have the x-pipe.

[ZBrink]

Originally Posted by Mikey

Do not wrap exhaust. It will only lead to corrosion.
Do you have an x-pipe in the center just aft of the transmission?

I just double checked and I do have the x-pipe.

[XfireZ51]

What Karl is describing is what was done w the C6Z. In order to reduce weight, Corvette went w an Xpipe rather than a resonator, and to duplicate the effect of the resonator, they adopted a muffler valve, the NPP. The system he described is what I now have on my ZR using a manual electrical switch to acivate the valves.