Can anyone give logical explanation why the car would tend to boost spike with extra restrictor pill in Stock turbo wastegate/actuator vaccum line?

Don't have much knowledge in fluid dynamics

 

The more restriction in that line, the higher the boost. Less restriction = lower boost.

 

That pill slows down the air getting to the wastegate actuator. Imagine it like traffic, if you have a 5-lane freeway the traffic can get from A to B quickly. If you choke it down to one lane in the middle, it slows everyone down bigtime.

Since the air goes through slowly, the actuator opens slowly. The longer the actuator is shut, the more boost you run. This is how boost controllers work, they regulate the amount of air pressure going to the actuator, kind of like having traffic lights on the freeway regulating the flow of traffic. If you want max flow, put all the lights to green, no flow, put them to red.

The big problem with the stock boost control system is it's designed for a stock car with a stock cat, stock cat-back, stock exhaust, everything. When you start getting out of the parameters that it was designed for you run into overboost and spiking.

Dale

 

adam, I had known that much. Still Thanks.

So it has nothing to do with Venturi effect or something?

Dale, Good explanation and appreciated. Thanks!

 

venturi effect is more associated with measuring pressure drops. wastegate pill is the flow metering/regulating view of bernoulli's principle.

the wastegate is a flow through actuator and the pressure differential between each side of the pill is negligible when the actuator is moving. how fast the pressure gets from one side to the other is what's of more concern in this case.

like Dale said, small hole=slow traffic. big hole=fast traffic.
(dont think too much into it and say, "smaller hole accelerates fluid faster" because the volume of air that is passing is still less than the volume of air through a larger hole.)

 

If there are two pills in the line, its likely that one of them is from the prespool line. If this is the case, the pill with the larger orifice belongs in the wastegate line.

 

Yes, there's nothing unusual about the stock boost control system. The Supra's, Sylvia's, and many other cars of that era use a bleeder solenoid with an orifice (restricter pill). This is very common on current Subarus for example. Once you start modifying you have to change wastegate duty cycles (not possible with stock ECU on this platform) and/or change the pneumatic aspect (solenoid, pill, hose).