When you bang your foot down the plenum chamber see a -ve pressure, ie the suck on that pipe disappears for a short period, this causes the WUR to reduce the control pressure, this is the pressure that stops the plunger in the metering head from rising any further. Therefore for a short period you get a richer mixture !!
Great ,so that means it is vacume or boost sensative,as I am turboing the car using the K-jet I need some way of making the mixture richer under boost so this may work
Well i don't know... i've always found it quite ambiguous... The underpressure on a n/a engine lowers the control pressure by moving the membrane in the WUR... so the mixture becomes richer... good... Now on a forced induction engine will the pos pressure not lean the mixure out then (higher control pressure) when on boost ? But then maybe the control pressure doesn't need to be lowered on boost because the compressor of the turbo really sucks the metering plate upwards ? in fact even a little more control pressure is wanted to get good air/fuel ratio? I'm not sure about what effects exactly take place in a turbo setup... that's why i'm using a turbo WUR (off a saab 900 turbo) to be on the safe side... i should (if i find the time) do some tests to really know what goes on and how n/a WURs are different (or not) from turbo WURs...
The Saab wur sounds a good idea as it was designed for the job,what year did it come from?,also are you using anything to ajust the timing during boost?
Yes it's just a bit more comforting to use parts that came off a turbo engine and were designed for it... I'm going to use the saab WUR, fuel distributor, vacuum advance canister and the T3 turbo itself... this all comes off a 1982 saab 900 turbo... but you can use audi, volvo, etc k-jet turbo stuff as well... (I'm not saying i won't have to tinker with the fuel distributor and/or the allen-srew in the WUR to get acceptable air/fuel ratios) The vacuum advance canister advances like a normal one, but can also retard while on boost, looks like it's simply a case of the pressure being able to move the arm in the opposite (retard) direction as well a bit...
I'm using Audi 100 WUR on my MK1 16v 9A and Volvo fuel metering. Good performance. I have Volvo 240 turbo WUR wanted to put in after swap in the new head. (P&P) Hope can get some hp increase.....
