The 550 Exhaust PATENT explains why the valve is there

Here's what kind of Ferrari Test and Evaluation driver I am:

Right now, I've got the only street 550 in the world with a (prototyped and custom fit-tested) Hyper-flow tuned exhaust system (cats and x-pipe, feeding into Quicksilver "silencers").

Soon, the engine will be responding to a custom-designed power load curve, "dialed in" via cam tuning by Dave Helms of Scuderia Rampante, Boulder (using engine cam data from a GTO250 racer that ran on the torque-intensive Nurburgring).

Right now, the MELLOW YELLOW MARANELLO is so powerful it's literally eating the rear tires- or the brakes if ASR is left on- ALL the time: At 50mph on irregular pavement...moving off from a standing start... at 130mph (which is as fast as I now dare drive, and have all mid winter, on what are becoming racing slicks!)

With this tuned exhaust, the engine's throttle response is 15-20% faster and my gear shifts HAVE to be right on - or you feel your mistake shake a 4,000 pound car, even at 100mph! The torque curve now goes right past its former plateau of 5,000 rpm.... and the engine will pull all the way to shift points in the 6,000's (although I usually shift below 5,500 to spare the engine).

The sound? When I go under a highway overpass, it sounds like all hell breaking loose on the uphill portion of Monte Carlo...50 meters up from the hairpin turn, where the F-1 engines are again sucking air in volume!

Actually, I think the car's now TOO loud!
Maybe I'm not insecure enough about needing people to look at my LOUD FANCY YELLOW FERRARI IN YOUR FACE! Standing behind it at idle, you can hear the exhaust pulses from the engine.... so distinctly, it's like listening to a trilling musical instrument: You can hear each cylinder firing... in rapid order...individually.

Maybe I'm just not insecure enough. But I'm doing test and evaluation of ALL the car's performance parameters, as a result of this tuned exhaust (and now cam) upgrade. And noise is noise- unless it's helpiong performance. Nobody was listening to my engine- except me- last June 10th, when I did 191mph... UP a 3% grade! That was two months before we did the fit evaluation on the Hyper-flow cats (now, I'd easily do over 200mph on that same two mile running start hill climb!)

No, it's this simple: My Ferrari is now TOO gnarly and LOUD! But what will happen to performance if I "tone it down"? I asked a lot of people. And nobody really knew for sure why the 550's OEM mufflers (er "silencers") had the valve assembly on the one barrel. Troy of Hyper-flow thought the valve might simply be a noise-reduction device (and he was right, as I found out when I read the Ferrari patent tonight). And Josh of http://www.Exoparts.com told me that many of the Euro performance cars had this type of exhaust valving, so it made sense that it couldn't be TOO performance- depressing (if Lambo does it and Porsche and Mercedes, etc).

There were two general theories about the OEM 550 mufflers and valves: 1. They provided noise- abatement. 2. They enhance low-end torque as a result of increasing exhaust back pressure.

And then there is the PATENT (#5,301,503):
Mr. Paolo Martinelli submitted the application for the Ferrari patent (for a GT car exhaust system)in 1992. And the U.S. Patent was granted in 1994.

The patent describes how, in engine exhaust design, "...a trade-off is invariably involved between the characteristics of the engine and the exhaust system... generally reults in impaired performance...particularly at high speed."

The Summary of the Invention is "to provide an internal combustion engine exhaust system enabling optimum operation of the system as a function of engine speed."

As I show in the attached illustration, inside the 550 silencers there are two types of pathways for exhaust gasses: The upper "Interference type" which utilizes Heimholtz resonating chambers to create wavefront interference - between exhaust pulses- to attenuate the sound. The other pathway (which has the external barrel's valve assembly to shut it off at low speed) is a less-restrictive type of silencer called a "Dissipative type". This is simply a perforated pipe, surrounded by a packing of steel wool...with the engine vacuum-actuated valve placed in the end of the pipe, where it's closed at low-medium rpm.

The patent describes how the Engine Management System of such a GT car would monitor rpm, throttle opening angle and intake vacuum (to determine the "load" on the engine). At variable moments in which the engine load is above a computational threshold stored in the EMS ROM, the EMS throws open the "vacuum actuators" on the mufflers...and the exhaust flow is increased for maximum top-end performance.

Actually, the patent does not describe ANY low-end performance. Instead, it refers to the fact that this invention, "...provides for optimum performance of engine by enabling greater output at high engine speeds, while at the same time maintaining a more than acceptable degree of noise attenuation... (of sound waves) being produced predominantly at engine speeds well below those corresponding to maximum output of the engine.

"In other words" the patent goes on, "the present invention provides for dynamically adapting the characteristics of (the) silencer to the operating conditions of engine... thus preventing output at high engine speed from being impaired solely for the purpose of attenuating noise at medium-low engine speeds, as with known exhaust systems."

The patent basically says that at low-to-medium engine rpm's, the 550 OEM muffler's closed valve
doesn't interfere at all with the adequate passing of exhaust gasses. And at high rpm and load (when the valve opens) then the exhaust's path is right down the less-restrictive "Dissipative" tube...and out the open valve.

So, in conclusion, I've decided now to create the first hybrid OEM/aftermarket mufflers in Ferrari history! I'm unbolting the OEM valve/ exhaust barrel assemblies from the OEM mufflers. And I'll have them welded to the exterior cases of each of my aftermarket Quicksilver mufflers (which have two dissipative pathways- no Heimholtz chambers).

The result will be that I will have a wide-open, unrestrictive (dissipative) route for low rpm exhaust through the Quicksilvers... AND a quieter car at those rpms because the other pathway will be blocked by the closed valve. Then, at higher rpms, the other dissipative chamber will be wide open, as the 550'e EMS throws it open to match the mapping of the ROM in the EMS. The net result will be that I will ensure, as the patent concludes, "...improved processing of the exhaust gas at high engine speed... also provides for more or less completely mixing the exhaust gas... thus further reducing pollution at high engine speed, and ensuring a fine balance of the exhaust back pressures of the two (cats)".

When this is done, I'll bet that if I "stomp" on car at 3,000 rpm in second or third...that the burst of additionalo sound (from the now-open valve on the Quicksilvers) will be just as incredible as the sudden blast of torque that already twists the car's rear to the right when I shift gears! Ah, FERRARI!

So I sitting on my deck in North Carolina enjoying my gin and tonic, when off in the distance I hear a high Reving engine. hey, WYo, could you turn it down alittle

Great reading, thanks for sharing all your hard work. Bob