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salcolkat asked: GM says the 2019 ZR1 is the loudest production car they have ever made. Can you explain the difference between the exhaust system on the Zr1 vs the ZO6 and the reason it is louder.
Tadge answered: The LT5 engine in the ZR1 produces 105 more horsepower than the LT4 in the Z06. To do that, it uses a larger blower at higher pressures to force a greater volume of air/fuel mixture into the same sized cylinders resulting in a more powerful combustion event. That also means more pressure on the piston and more torque at the crank – higher output. It also means a larger volume of exhaust gas pushed through the tail pipe and muffler. Bottom line is that we start with more acoustical energy with the higher output engine.
Corvette has been a pioneer in active exhaust. We use a variety of strategies to give people options on how aggressive they want their car to sound. For ZR1 we have taken it a step further by adding internal, passive valves (shown below) that effectively act as a continuously variable orifice instead of the fixed perforations that most manufacturers use to muffle sound. We do still add in fixed perforations (on the “Chimney” in the pic below), but they are much smaller than any of the previous C7 muffler tunings. The smaller these fixed perforations are, the more aggressive the car will sound. Why not eliminate them entirely? Because, even in this car, we are still balancing aggressive sound and refinement, or sound quality. The passive valve allows this tuning change to be possible, and allows the ZR1 to sound extremely aggressive. It acts as a type of acoustic by-pass giving the car a tuned straight pipe type of sound. It is very easy for someone to cut the muffler out of a car and just run straight pipes, but that solution can sound coarse and boomy at lower speeds. The passive valve allows us to have a straight pipe-like sound, but then also have a quieter, less aggressive mode as well.
Most Corvettes have electronically controlled valves on two of the four exhaust tips. You can see those on the rear of the car if you look under the fascia. Those are the key components in our sound management strategy. Under light throttle those valves stay closed and force the exhaust gas to take a torturous path through the muffler. This is true for Stealth and Tour Modes in the ZR1. Sport and Track modes have the electronic valves open far more often. Even in these “Quieter” modes (Stealth/Tour) these electronic valves will open around 4000rpm’s for backpressure reasons. We don’t recommend using stealth or tour on the track since it will retain heat in the exhaust system and probably not help with certain track’s sound limits (because the valves will open under full throttle). In the picture below, which shows a portion of the muffler internals, the electronic valve is not seen because it is outside the muffler and resides on the main flow pipe. When the electronic valve is closed, it creates back pressure that forces open the passive valve in the illustration. The exhaust is forced to expand into the chamber created by the muffler can and pass through multiple perforated barriers and out the secondary flow path. So under light throttle and relatively low flow conditions all of the exhaust exits through the center two exhaust tips. As the driver adds more throttle, more gas passes through the passive valve opening it up wider until there is enough throttle for the electronic valve to open.
Once the electronic valve is open, there is minimal back pressure and the passive valve closes. In this case, most of the exhaust will take the path of least resistance and that is straight through the main flow path. Under these conditions almost all the exhaust exits the outboard exhaust tips. This is why you see the outboard tips dirtier than the inboard tips if the car has been used on track or driven hard. The Z06 and other Corvettes with NPP have fixed orifices in the main flow path in place of the passive valve, so even when the electronic valve is open, there is some leakage over to the secondary flow path. On the ZR1 there is minimal leakage and the sound is a tuned straight-pipe…. much like a race car.
The engineers who invented this system have applied for a patent and I fully expect it to be granted.
As in many things in automotive design, there is a lot of technical engineering, but also an element of art. To be honest there is even some trial and error. Tuning exhaust systems is both and art and a science and we are still learning.
Excellent response Mr. Juechter. Thank you very much for this concise explanation. After reading this I do believe it will kill the after market exhaust system business. Absolutely no need to change out the OEM system !
I guess the next question is how would this system or a similar version sound on the Z06. If it was available and sounded as good, relatively speaking with less pressure and a smaller supercharger, would your engineers build it for performance parts. I would rather spend my money with chevy than on aftermarket Just thinking and asking.
I guess the answer would imply that with a bigger blower and very similar HP on my Callaway 757 I would get a similar sound by putting the ZR1 mufflers on my car.
Thanks Tadge. As usual, very good explanation that at least some us "gear heads" appreciate! It was well written and basic enough that anyone who doesn't want all the details can understand that it happens for a reason!
04-25-2018, 04:06 PM
[ANSWERED] ZR1 vs ZO6 exhaust system
