Exhaust Bypass Valve Operation

Hi,
reason for this by-pass valve is the legal requirement concerning exterior noise. All passenger cars needs to fulfill to a max of 75dBA exterior noise. This is measured via two microphones standing 10m from each other (left/right). The measured car is then with wide open throttle acceleration from 50 to 60kph, running exactly in between both microphones. This should then not exceed 75dBA. Hence, many brands have features to lower the exterior noise in the afore mentioned speed band. That might be via exhaust valves, or via engine software. Examples are limiting the max power when you give wide open throttle at exaclty 50kph (not 49, not 51). Doing so you produce less exterior noise. That is the cheapest solution for passing the criteria. Lucky though our cars do it via a tuned exhaust valve............

 

... so how can I open the valve indefinitely?

 

Hi Terry, correct Corvette is using the same kind of exhaust valve control as Aston Martin is doing as well (Vanquish). The point that the valve is closing the exhaust at different rpm's when comparing 550 with Vanquish or Z06 is due to the different gear ratios. The homologation test is done starting at 50kph to 60kph full throttle. Yet no automotive brand will admit that this valve is there feature to fulfil the homologation, instead prefer to publish torque increase. That torque increase is indeed the case with open valve, however very marginal.

regards, Jan

 

TAZ those are nice clips from your manual with great pictures? What manual is that from. Is it an official ferrari 575 manual or something else?

 

Nice work as usual Taz!
Mine were bypassed just as described ( Vacuum hose to T, solenoid with c-shaped tube from inlet to outlet to prevent anything entering it.... )
(Any chance you can upload the files to a file-sharing server like Depositfiles / Filefactory etc..? )

 

With the right hoses, connectors and a stopcock, I bet it's possible to have a switchable system. One could always go back to stock if need be.

Barry

 

True that!

 

Terry, does Corvette provide the cockpit selector as standard equipment?

 

Thanks Taz. Hopefully that becomes a bit more clear when I get under the car.

-Joe

 

Ferrari has always been very up front about the bypass systems being for noise requirements.

Eliminating bypass valve function on 355 is a known cause for real engine problems. It should be left intact.

 

RD,

Can you tell us why the 355 is different regarding engine problems if the bypass is deleted? Is it that whole issue of hypothesized exhaust gas reversion in the 355 that other ferraris do not have?

Thanks!

 

It is not hypothesized. Ferrari knows of it very well and it is easily proven.

I recently had a 355 here that failed smog. After much screwing around I loosened the center pipe and slid in a piece of sheet metal. It instantly ran correctly and cleaned up. There was so much backwash that the air was cooling the cats and making the O2s think there was too much O2 and ran the mixture full rich. Blocking the center pipe made the O2s calm down and operation differences could be seen on a scanner. The cats heated back up. I could see it all real time on SD2. It made the car run clean, correctly and it finally idled good. Also it has been well established that the back wash gets clear to the cylinders. It has been causing much of the advanced cylinder and ring wear we have seen on many motors. At low exhaust flow the motor just keeps reingesting its own exhaust. The degree of the effects change with different exhaust systems.

Its no myth. Ferrari has known about is since they built the cars.

The exhaust tract of the 355 is short. It is eight feet from the tail pipe tips to the cats in a 550 or 575. Even 360 has a longer exhaust tract than 355.

 

They have been told before. They just want loud noise so everyone will look at them. I prefer to be quiet so no one notices.

 

The kit I have uses the factory HomeLink button on the sun visor to operate the muffler bypass valves. The choices are always open or follow the factory algorithm, which i believe opens the valves at 3000 or 3500 regardless of throttle position or load.

Jeff

 

I think its more like a guy with a P51 who likes climbing out at 3000rpm and 60 inches on 110 low lead. Sure sounds cool but you can use your Timex for an hour meter.