How do I pick a wastegate spring to work with a manual boost controller?

[dpuma8]

I have an N42 block with dished pistons, N47 head, 38mm Tial wastegate, Megasquirt, 550cc injectors, and a GT3076R .64 turbo ready to go on my car.  From what I am reading on this site, the N47 is not a good head to run boost on so I am planning on running 5psi until I can find a P90 head.  I have purchased a cheap manual boost controller but I do not know what spring I need for the wastegate.  This car is street driven and will never see the track.  I eventually would like to see 15psi.

 

Can anyone recommend a specific spring that I need for my setup?  I am super confused as to what spring to get in conjunction with a manual boost controller.

Edited April 12, 2016 by dpuma8

[mtnickel]

I have an N42 block with dished pistons, N47 head, 38mm Tial wastegate, Megasquirt, 550cc injectors, and a GT3076R .64 turbo ready to go on my car.  From what I am reading on this site, the N47 is not a good head to run boost on so I am planning on running 5psi until I can find a P90 head.  I have purchased a cheap manual boost controller but I do not know what spring I need for the wastegate.  This car is street driven and will never see the track.  I eventually would like to see 15psi.

 

Can anyone recommend a specific spring that I need for my setup?  I am super confused as to what spring to get in conjunction with a manual boost controller.

Well if you need to run 5 psi early, then you will certainly need a 5psi spring.

 

As for what spring to use when you go up to 15psi, there are a couple things at play.

 

1) if the spring is too soft (low PSI), then even if you use a MBC, you may not be able to get very High psi's as the wastegate flapper will push open.

 

2) The degree to which the above will happen depends a lot on the size of the diaphragm in the wastegate. With an external gate, I wouldn't be surprised if you could hold 15psi even on the 5psi spring.

 

3) I would however choose about a 10psi base spring. I feel that the closer your spring is to your MBC setting, the more stable the MBC operation will be.

 

Hope that makes sense.

 

Mark