Exhaust Valve Actuator for Low Vacuum

[jj911c2]

I recently installed a 997 GT3 exhaust with valves on my car. It sounds much better and does not drone.

The issue I am having is I can't get the valves to fully close (I only get about 30% closed) as the engine (3.8 with ITBs/big Cam) does not produce much vacuum - about -4.5 at idle and -6 PSI when cruising at 3k RPM. Does anyone know a source for actuators that close with a lower vacuum? I put a vacuum pump on mine and it takes about -12 PSI to fully close -- if I could find one that closes at -5 or -6 PSI it would solve the issue. Picture attached of valves. I did wire them shut and went for a drive and the difference between fully closed and 30% closed is significant.

[targa72e]

other option might be try using a one way valve with a vacuum reservoir. This is what was used on many production cars. Rev the engine one time and engine decel will create enough vacuum to hold closed. Then use a solenoid to open valve at selected RPM and load for loud exhaust.

john

[wallra]

just install a electric vacuum pump.

[jj911c2]

Thanks targa72e & wallra. I will look into the reservoir or vacuum pump option.

[JackkTheMackk]

That’s not the issue, I have the same exhaust from Brian. I have dc60 cams in my 3.2ss with a ton of overlap and I still have sufficient vacuum even at idle to close the valves all the way with no problem. It wasn’t like this at first and what I had to do was take that circlip off, break the jam nut free, and spin the rod coming out of the actuator in to the actuator all the way and then retighten the jamb nut and throw the circlip back on.

If you reach down with the car off, it will have a ton of free play. With a cold engine and the valve closed and the car running, you can push the rod and see that the linkage adjustment isn’t right.

Personally, I would prefer the valve to live in the closed position rather than open. That way during start up and if there’s any failure, it will stay quiet. I would not do electric as they fail fast from the heat and vibrations. Adjust the linkage and see if it solves it.

[jj911c2]

Thanks Jack. I did go out and take off c-clip, jam nut and even cut a bit of the threads off to get more travel. I can set it up for fully open with no vacuum and 50% closed or fully closed on vacuum but only 50% open full throttle -- just not getting vacuum to get the actuator to move enough. If I could get an actuator that fully travels at -6PSI it would give full range.

[JackkTheMackk]

Originally Posted by jj911c2

Thanks Jack. I did go out and take off c-clip, jam nut and even cut a bit of the threads off to get more travel. I can set it up for fully open with no vacuum and 50% closed or fully closed on vacuum but only 50% open full throttle -- just not getting vacuum to get the actuator to move enough. If I could get an actuator that fully travels at -6PSI it would give full range.

Do they jingle? My jingled before messing with the actuators. Have you bench tested your actuators with a hand pump and gauge to see what PSI you need to fully close?

What cams are you running? I imagine with EFI you would have slightly more vacuum and less overlap than me. My valves have no problem closing at idle along with sufficient vacuum at my brake booster for my stop tech big brake kit, all while vacuum is only tapped from cylinder 2 on my pmo intake manifolds.

[pampadori]

Could you switch to electric valves and use the ECU to control them based on map signal and RPM?

[jj911c2]

Originally Posted by JackkTheMackk

Do they jingle? My jingled before messing with the actuators. Have you bench tested your actuators with a hand pump and gauge to see what PSI you need to fully close?

What cams are you running? I imagine with EFI you would have slightly more vacuum and less overlap than me. My valves have no problem closing at idle along with sufficient vacuum at my brake booster for my stop tech big brake kit, all while vacuum is only tapped from cylinder 2 on my pmo intake manifolds.

I did test with a vacuum pump and they need about -12 PSI to fully close. I am only getting -4.5 PSI at idle and -6.5 at cruise. The actuators were not that loose -- only a few thread turns to take all the slack out. CAM is webcams 290/291 grind with 294 duration intake/280 exhaust. I have all six ITBs going to a vacuum block that I tapped off of for ECU MAP and exhaust valves.

Originally Posted by pampadori

Could you switch to electric valves and use the ECU to control them based on map signal and RPM?

This may be the way to go -- just requires modifying the exhaust and welding the electric valves in and programming ECU which would give more control than just vacuum.

[RarlyL8]

If the vacuum manifold doesn't produce the signal needed to properly operate the valves you can use a vacuum reservoir and then add electronic controls. Transplanting electric valves would not be simple and they are generally not as robust as the valves we use. I tested a bunch of valves long term and most failed in a few months.