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1.9TDI ~ 200hp with 35mm or 38mm Wastegate

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Hey, i'm currently building MK3 Golf TDI (1Z engine). VW is well known for issue with wastegate so i picked up a turbo from Golf 2 1.6 GTD (~180-200hp capacity). I already did EDC15VM+ swap on my car so i will not have too much problems with remap :) What i want to know is, which wastegate should i choose 35mm or 38mm? For the spring i know that it must be on the half way from boost, which means if i run 30psi i need 15psi wg spring, but what if i put 11psi spring on 25 or 28psi of boost? Btw stock wg valve is 23,2mm

The wastegate size is actually only part of the consideration here. You also need to factor in the way the wastegate is integrated to the exhaust manifold, as poor integration will require a larger gate to achieve control - in some cases if the integration is terrible then it may be impossible to achieve good boost control irrespective of the size of the wastegate. I'm not familiar with that particular engine but I'd probably suggest a 38 mm wastegate to give you the best chance of success.

Where will you suggest me to put wastegate on exhaust manifold? I tought to install it between 3rd and 4th cylinder... Btw i'm building manifold from scratch.

Here is a diagram of the best way to do it if you have the room:

https://www.turbosmart.com/wp-content/uploads/2011/10/5529.jpeg

and this on what to avoid:

https://www.theturboforums.com/attachments/wastegateplacement-jpg.662720/

Thanks David, i have just ordered 38mm wg :)