Wastegate & Spring rate. Help me understand this!
 

Hi,

I have searched but didnt find an answer. If i run wastegate without boost controller. Do i get the spring rate as max boost pressure?
example:
7 psi spring = 7 psi max boost? when the wastegate will open and when it will close?

Re: Wastegate & Spring rate. Help me understand this!
 

Wastegate creates a pre turbo exhaust leak controlled by air charge pressure that pushes/overcomes the spring and opens the wastegate.
Boost controllers "hide" this boost pressure from the spring untill greater pressure is reached.
No boost controller can make the spring softer :) So spring is allways the least pressure.

Re: Wastegate & Spring rate. Help me understand this!
 

It depends on a number of factors. Springs are rated on approximate operating pressure. Ideally a 7psi spring would be in the 7-8psi area. Springs have a "cracking" pressure which will be lower than the advertised pressure. This cracking pressure is when they start to compress and open the wastegate. They will slowly continue to compress until you reach the advertised operating pressure where they will be fully compressed and the wastegate will be fully opened. The wastegate will close again as soon as the diaphragm in the wastegate stops seeing pressure like when you let off the throttle. Exhaust flow, turbo size, wastegate size, ignition timing, etc can all play a part in the actual boost you see regardless of rated spring pressure. As stated above the set spring pressure will always be the lowest operating pressure.

Some boost controllers work by bleeding off some pressure/airflow to the diaphragm so that the wastegate opens later and operates at a higher pressure rating. Others work by introducing positive pressure on the opposite side of the spring to increase resistance which also allows the spring to work at a higher pressure rating.

Re: Wastegate & Spring rate. Help me understand this!
 

Both of the other answers are awesome. You're looking for simple..
Running on WG pressure without a boost controller, yes, you will see the spring pressure +/- 2 psi. If it is a 7 psi spring, you'll see between 5 and 9 psi max, IF the wg is functioning properly. The Wastegate is always closed. It opens once the spring pressure is reached.

Re: Wastegate & Spring rate. Help me understand this!
 

Thanks for the replies guys. Now i get it.