My '83 308 GtSi, greymarket Euro QV has no vacuum limiting valve and no fittings that I can see where one may have been. Should I worry and try to put one in, or does the Euro version not need it? thanks
There's a recent and related thread I started at http://www.ferrarichat.com/forum/showthread.php?t=308489 I'm still trying to understand how necessary the vacuum limiter is on a non-emission-controlled car; hearing that your Euro car doesn't have one suggests that may not be very necessary. It would be interesting to hear from some other non-NA owners, see whether they ever had the thing. FWIW, many other US-spec cars of that era have devices that similarly keep metered air flowing when you get off the throttle suddenly: dashpots that slow the throttle closing on many smog-era weber carbs, for example. In those cases, the idea is to prevent misses on deceleration that will dump unburned fuel into the exhaust stream where it will damage the cats or backfire intolerably when mixed with air from a smog pump. Obviously this is only a concern on an emission-controlled car with cats, thermal reactors, smog pumps, EGR, and the like. Generally letting an engine run way lean is a Very Bad Thing(tm), but under high-vacuum closed-throttle overrun conditions, the combustion chamber pressures are so low that even a very lean mixture won't hurt anything.
The Euro 308QV SPC illustration structure and numbering order indicates (IMO) that the Euro 308QV "evolved" with the early cars having the AAV mounted on top of the engine near the water pump and no vacuum limiting valve, while the later Euro 308QV have the AAV mounted to the coolant expansion tank and do have a vacuum limiting valve. Is your AAV mounted on top of the engine near the water pump or to the coolant expansion tank?
The only place the vacuum limit valve can go is on the throttle body as its purpose is "throttle bypass". So, if yours doesn't have any taps / fittings for valve plumbing ---- then it never had, and was never supposed to have, one installed. As long as your car still has all of its original ignition system, and critical CIS system components, everything will be fine. If any of that has been altered, you may have a problem. Also, the early Euro injected cars didn't have the excessively retarded ignition maps that the US cars had. They also had slightly richer fuel delivery across most of the lower load range --- so, not as much need for a vacuum limit valve. As I mentioned in the other thread referenced above. The vacuum limit device is a device that actually increases the fuel mixture delivery under certain load conditions --- therefore, it is not an emission control (i.e., to lower emissions) feature. It protects the engine from lean misfiring ---- which is not as necessary on the Euro cars due to their richer mixtures and less-retarded ignition curves.
The 308 has the AAV under the expansion tank but again, no taps that I can see. From the look of things, it seems to be all original down to the braided hose covers. On deceleration the engine "burbles" a little but doesn't sound lean.
