Defeating the Exhaust Bypass Valves

While digging for some old notes for another thread I ran across this and thought to post again for those that might have interest.
Defeating the Bypass Valves. Anyone that can jack their car up safely and turn a ratchet can do this. The only 10 mm screws you turn are on the rear bottom under panel of the car to remove it (9 screws). From there No hoses to cut, you just reposition two on them. All right in front of you.

It is a subtle but nice increase in sound. Far from resonance with stock silencers and about 30 to 40% of what late gen Tubi's sound like. It gives the car a more fitting idle and sound for driving. You will be hard pressed to find any lost torque by doing this.

It cost nothing but a few minutes, can be reversed in the same amount of time. Once the rear lower under panel cover is off, find the vacuum hoses running from your exhaust bypass valves at very rear (near tips) of mufflers (a.k.a. silencers). Backtrack to vacuum "T", then backtrack again from the vacuum "T" with the single hose to solenoid, a very short distance. Now that you have the solenoid identified, go back and remove this last single hose that you followed up to the solenoid but, remove it at the vacuum "T". Leave this hose loose for now, go back to the solenoid, at the twelve o'clock position carefully remove the top vacuum hose, by twisting, wiggling and pulling as gently as possible upwards. Once removed, take this hose (12o'clock hose) and connect it to the open vacuum "T" that the short hose had been connected too. Then take the short vacuum hose that is still loose and reconnect it to twelve o'clock position on solenoid (creating a small loop). That's it. Doing this you have attached the accumulator hose from front of car to vacuum "T", directly activating the bypass valves to open upon start up. They now stay open with car running. The other small hose has simply covered the open hole on solenoid to prevent dirt from getting in.

Last, replace bottom rear under panel.
I don't think anyone with stock exhaust would not enjoy this subtle improvement in sound.
Bill
FL

 

Nice write-up, Bill.

Barry

 

Bill- That sounds familiar.

 

For which car is this? 456/M/550/575?

 

All with fail closed exhaust valves. Note early 456s do not have much of a vacuum system (or valves), even the brakes are hydraulically boosted. Idea is to provide vacuum all the time to keep the valves open. What Bill wrote works without needing any additional hoses and plugs all the holes so nothing gets into the system or parts. The valves can also be wired open, but that is a way less elegant solution.

 

Very good tutorial! Thank you