Trying to understand stock wastegate function

[Eric Fischer]

I am doing some shakedown testing with the new mods in my sig. I am using a fishtank bleeder valve to control boost on a stock turbo.

Boost control is absolutely horrible with this setup. On launch it will peak to 21-22 PSI and then at higher RPMs the boost falls off to about 12 PSI (probably because the turbo is too small). But then when it shifts into O/D boost will come back up to 19-20.

In any case it's my understanding that if the wastegate is fully open then I should get nearly constant minimum boost levels. So I tested this idea by closing the fish tank valve (which essentially means that there is a direct connection between the compressor and the wastegate actuator). Well this did change how the turbo responds, the tendency to overboost on downshifts is nearly gone but maximum boost is still erratic with a low of about 12 PSI and still spiking to 19-20 at WOT.

If everything is functioning properly and with a direct connection between the compressor and the wastegate actuator, shouldn't the boost remain nearly constant (wastegate actuator spring pressure)?

Thanks.

 

[dgoodhue]

Re: Trying to understand stock wastegate function

Base boost is suposed to be around 9psi. Pull the fish tank valve and directly run a vauum from the actuator to to a vauum source. (You don't have the solenoid still connected to the ECM and vacuum source?) If this still give you erratic boost control (or more than 10psi), you have a bad accuatoror or a sticking wastegate puck

BTW your not going to able to control boost spikes with the stock turbo wastegate and any type of manual boost controller.