pcguy2u

After much testing, pushing and shoving with the service department and attempting on my own to find the source of the exhaust drone, it appears that the drone is coming from the by-pass (center) tailpipes.

My question is how are these tips constructed and what are the perforations for?

Let me explain - in the end, it came down to capping the two center pipes using large hose clamps and the bottom of two cottage cheese containers, like this:


With the caps on, the exhaust is less noisy at idle and has no perceptible drone under very very slight acceleration, which is the basic problem.

At first thought, one might conclude there's something wrong with the NPP valves, but the valves are closed tightly, the springs are also very tight and I have fully tested all the vacuum lines, connections and restrictors and found no anomalies.

So it boils down to whether I should make a stab at the service folks reluctance to do any about this. The defining answer to this puzzle is whether these tailpipes actually bypass exhaust through the perforations when the valves are closed.

Everyone I have received a response from, in other threads I've started on this issue, has said their exhaust makes no drone under slight acceleration. One response was from someone with a ZR1 whose exhaust was dead quiet under these circumstances and who has 2+ times the 9000 miles on this Z.

So if the perforations do not actually by-pass exhaust, there should be no sound or exhaust coming from the center tailpipes at idle. In this case you can put each hand over the ends of the pipes and the sound goes away and you can feel the exhaust your blocking.

The drone is getting progressively worse.

So what do the perforation do for the exhaust if they don't actually bypass exhaust?


BTW, my 3/36 is up in September.

narush

I LOVE MY B&B Exhaust

Loud as hell and it shoots flames what more can you ask for - LMAO

0Anthony @ LGMotorsports

Below is assuming that the valves are actually closing 100% when the car is at idle and below 3000 RPM...after that they open.

Pull them off and put on a set of 2006-2010 (early) Z06 mufflers on the car.

The ZR1 uses the same kind of muffler like the base cars do. They both use a resonator on the tip and almost wide open section on the open side. This would be the factory 'muffler mod' that most of the Z06 guys do.

If you put on a set of the normal Z06 mufflers on the car you will notice that the mufflers have solid tips and the open side is actually muffled as well.


A Z06 muffler is a direct swap and I'm sure there are a lot of Z06 guys that would be willing to swap you for them. Just note that the car will be quieter.

camille

Can you describe the drone in more detail? Can others hear it outside of the car?

I had an unusual exhaust sound only heard at certain rpm's on my previous '09 ZO6. I guess I could call it a drone, and it was related to vibration of the butterfly valves only at certain rpms. Definitely a bizarre sound that I could hear inside and outside of the car. The dealer demonstrated it for me, then replaced the muffler assembly under warranty - no more drone...

3LZZ06

Have you tried riding in another ZR1 as a comparison?

You might find they're all the same...

pcguy2u

Very helpful - the drone is totally absent while cruising at any speed.

The slightest bit of acceleration causes the drone to start and it gets worse as you press further on that right pedal. Of course we all know what happens when you press a bit further.

pcguy2u

Hey Scott, maybe you could try to see if you can feel any exhaust while your valves are closed and the engine is idling?? Also, if you cover the center piipes with your hands (or a piece of cardboard, or?), is there a difference in the sound at idle?

Or as the owner of the only other ZR1 I know of about (70 miles away) put it, "mine is dead quiet under slight accelleration".

Finding a ZR1 is not too easy - the guy above is the only one in two clubs (over 100 vettes) that I'm affiliated with.

No one has reported any kind of a drone on any of their ZR1's in any of the three threads I have started on this issue. The above post on the Z06 muffler replacement is at least proof that they will replace them.

Does anyone know if the exhaust falls under the 3/36 or 5/100?

BearZ06

camille

That's exactly what happened with my ZO6. Any acceleration would start the drone, and then at much higher rpms the normal engine/exhaust sounds would be louder than the drone itself.

The problem was there from day #1 with my '09 ZO6. Had I not previously owned an '06, I might have wrongly assumed that sound was "normal" for the car.

It was important for me to take the technician for a ride and repeatedly demonstrate the sound for him. Then back at the dealership, it took two technicians to isolate the problem to the butterfly valves themselves - oddly enough BOTH of them were causing this vibration, and there was no way to tighten or adjust them. The entire muffler assembly was replaced with a new unit and the car was perfect after that.

MachAll 2005

There was a post sometime back on a new GS Vert that had a drone that was corrected by replacing the new cat/X Pipe system ... http://forums.corvetteforum.com/c6-c...-gs-ideas.html
IF you car has the new exhaust system with extra cats you may want to check it out.

ufaj26

If you're getting some type of drone you should push for new mufflers under warranty. I would say the mufflers fall under the 3/36. I have not experienced the drone or butterfly vibrations in any of my ZR1's.

jcosta79

A quiet Corvette? I wonder what those are like?

camirocz

Sell it and buy a prius i hear they re really quiet.

OnPoint

No drone at all on mine when flaps closed. In fact you can't hear anything from the exhaust while in the cockpit driving (just a slight supercharger/engine sound, but that's it), and not a heck of a lot outside the car either. I regard the system as too quiet with flaps closed.

pcguy2u

How many miles on it?

Talked to the Service Manager yesterday and he agreed to replace the mufflers. Just wanted me to take a drive in one that the owner says is quiet and to then state that vehicle with similar mileage is quiet to my satisfaction.

Can't ask for more than that. Waiting for someone I know with a ZR1 to return from a trip. He says his is quiet also - just like everyone else who has responded.

I'll let you guys know the outcome of all this.

Thanks

OnPoint

Sounds like you're going to get fixed up.

BTW, mine has around 5,500 miles on it.

Gary '09 C6

Nick,

FWIW, with respect to this issue, I'm in the same place as Travis (also about 5K miles).

Gary

Shurshot

Manual transmission cars placed in a higher then optimum gear selection produce lugging that will introduce a low-frequency tone when prompted to accelerate.

This is why pinging from low fuel quality can often be heard better at low RPMs, and when at the same time the motor is forced to lug by attempting to accelerate without downshifting.

I'm not trying to tell you your business and I apologize if this comes off wrong, but maybe if you were more aggressive with your gear selection the drone will go away.

If nothing else it might be worth a try.

3LZZ06

I can almost say "Camry" quiet with the exhaust flaps closed.

Needless to say they are never closed...

pcguy2u

Met with the owner of a ZR1 in Napa on Friday and had a chance to drive his car - definitely much less drone and much less leaking from the center exhausts at idle.

Still trying to decide if I want to take the dealer up on his offer.