The vacuum advance (delay?) valve
Discussion
Thought I'd split off this thread to avoid polluting the "idling" one.
Seems there are different explanations even on the same websites:
http://tvr-parts.com/tvr-parts/part-details/tvr-e0...
The wording seems a little odd:
"Vacuum advance delay valve for the Rover V8 . This device acts as a restricter and limits the vacuum being supplied, and, therefore, the amount of timing advance available. Mostly used on the 5.0 engines, it can be a great help in controlling "pinking". Can be used on any of the Rover V8 models as fitted to the V8S Griffith and Chimaera."
https://classicroverforum.net/index.php?threads/va...
and
http://www.britishv8.org/Articles/Curving-Rover-Di...
Maybe it's just there to protect the diaphragm, maybe from front-firing.
Seems there are different explanations even on the same websites:
http://tvr-parts.com/tvr-parts/part-details/tvr-e0...
The wording seems a little odd:
"Vacuum advance delay valve for the Rover V8 . This device acts as a restricter and limits the vacuum being supplied, and, therefore, the amount of timing advance available. Mostly used on the 5.0 engines, it can be a great help in controlling "pinking". Can be used on any of the Rover V8 models as fitted to the V8S Griffith and Chimaera."
https://classicroverforum.net/index.php?threads/va...
and
http://www.britishv8.org/Articles/Curving-Rover-Di...
Maybe it's just there to protect the diaphragm, maybe from front-firing.
Discussed on here years ago:
http://www.pistonheads.com/gassing/topic.asp?t=970...
To save reading the whole thread:
Right, it took me a while to find it but here's chapter and verse from Julian (Joolz) Lane, formerly one of HHC's mechanics and now a race specialist. When the subject of the one-way valve was raised on the TVRCC mail list on Egroups in August 2001, Joolz' reply was:
"The valve thingy is just a restrictor that works better one way than the other. It restricts the vacuum communicated to the advance mech when on cruise conditions, so it will suck advance on, but only after several seconds of holding at light throttle. This prevents the advance coming on when you go through the cruise portion of throttle towards high throttle, when you lift off the throttle any vacuum that has been communicated to the advance unit releases quickly... the intention is not to add vac advance unless the car is definitely in a cruise state, so limiting the change of pinking under transient throttle conditions. So you should not be able to suck easily through one way and you should be able to suck easily the other way, and fit how it says on the valve otherwise you'll get vac advance sucked on and staying on as the vacuum doesn't then release quickly from the unit and you'll run with another ten degrees of advance all the time - not good."
So I think I've got my vac and bobweights mixed up...
http://www.pistonheads.com/gassing/topic.asp?t=970...
To save reading the whole thread:
Right, it took me a while to find it but here's chapter and verse from Julian (Joolz) Lane, formerly one of HHC's mechanics and now a race specialist. When the subject of the one-way valve was raised on the TVRCC mail list on Egroups in August 2001, Joolz' reply was:
"The valve thingy is just a restrictor that works better one way than the other. It restricts the vacuum communicated to the advance mech when on cruise conditions, so it will suck advance on, but only after several seconds of holding at light throttle. This prevents the advance coming on when you go through the cruise portion of throttle towards high throttle, when you lift off the throttle any vacuum that has been communicated to the advance unit releases quickly... the intention is not to add vac advance unless the car is definitely in a cruise state, so limiting the change of pinking under transient throttle conditions. So you should not be able to suck easily through one way and you should be able to suck easily the other way, and fit how it says on the valve otherwise you'll get vac advance sucked on and staying on as the vacuum doesn't then release quickly from the unit and you'll run with another ten degrees of advance all the time - not good."
So I think I've got my vac and bobweights mixed up...
Now for me, I would interpret that explanation as -
This unit delays more vacuum advance happening (on) but does NOT delay vacuum drop (off).
So therefore right way round is when you can suck air through it without resistance, the end in your mouth should go to throttle ?
How it actually works is complicated by exactly where the 'port' is drilled, which affects exactly where more vacuum happens.
Most are drilled close to the main throttle, so the port only 'sucks' at light thottle anyway...
That all seems to make sense.
This unit delays more vacuum advance happening (on) but does NOT delay vacuum drop (off).
So therefore right way round is when you can suck air through it without resistance, the end in your mouth should go to throttle ?
How it actually works is complicated by exactly where the 'port' is drilled, which affects exactly where more vacuum happens.
Most are drilled close to the main throttle, so the port only 'sucks' at light thottle anyway...
That all seems to make sense.
RCK974X said:
This unit delays more vacuum advance happening (on) but does NOT delay vacuum drop (off).
So far so good.RCK974X said:
So therefore right way round is when you can suck air through it without resistance, the end in your mouth should go to throttle ?
No the other way around, if your sucking the throttle end (applying more vacuum) then you should feel resistance.
RubbishFettler said:
I don't have one of these fitted at all, would that explain why i can't completely stop the car from pinking?
Steve
Can also be caused by too far advanced timing...Cheap fuel..And a spark plug that is too hot..I had this with BPR5..The 7's were too cold so I now use the iridium 6's...Steve
Not the same engine I know, but I found that going to RN7Y instead of RN9Y for the 2.8i engine helps with pinking - I was able to advance timing a little nearer original with the colder plugs. So far not had any fouling issues.
I also did that on my old tuned Triumph 2500 engine, and it also helped, but I did have to clean the plugs a bit more often...
I guess this would apply to all engines (more or less) that it's worth trying one grade colder than 'standard' 4 star leaded setup ...
I also did that on my old tuned Triumph 2500 engine, and it also helped, but I did have to clean the plugs a bit more often...
I guess this would apply to all engines (more or less) that it's worth trying one grade colder than 'standard' 4 star leaded setup ...
I did try colder plugs, which didn't make any difference to the pinking. I have also tried octane boosts, although not the valvoline one as suggested, so worth giving that a try. It also doesn't seem to make any difference whether I use normal unleaded or super unleaded. Don't get me wrong, the pinking is only slight, but I would like to get rid of it altogether. Reading this thread, it does seem to suggest that fitting the delay valve may assist, are these model specific or is it the same one for all v8 wedges?
Cheers
Steve
Cheers
Steve
RubbishFettler said:
Hi
Does anyone know if these are model specific, or is it the part the same for any of the Rover V8 engines?
Cheers
Steve
All the same, as far as I'm aware. The 390SE was derived from the 3.5, the 400SE flapper was the same but with a different bore (by 0.5mm!) and I'm not sure if the 400SE hotwire even has it fitted.Does anyone know if these are model specific, or is it the part the same for any of the Rover V8 engines?
Cheers
Steve
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