Welding To Cast Iron
My quest to run an external wastegate has led to a bit of a problem that people in many car communities have went back and forth about for years.
Most factory turbo manifolds (including the GTi-R ones) are made from cast iron. When welding other materials to cast iron you run the risk of it cracking. In addition since the two materials expand and contract at different rates you also run the risk of cracking occurring further down the line. Several people have modified GTi-R manifolds for an external wastegate, but I have yet to get a good answer as to how they held up over a long period of time.
The process of welding to cast iron is sensitive as well. From what I have read, the cast iron must be pre-heated, welded, and then allowed to cool slowly. I have found a local fabricator (JM Fabrications) that has been doing this to DSM manifolds for a while with good luck. Their process seems to be spot-on with what I have read as well. Their cost is about 1-2 hours of labor plus the cost of materials (This should be minimal). Once I receive the Synapse Engineering 50mm wastegate, I will bring it along with the manifold and turbo to have everything welded up. The turbo will have the internal wastegate flapper welded shut.
Why go through all of this and set myself up for a possible failure down the road? There are aftermarket turbo manifolds available for FWD SR20′s, but the problem comes with the rest of my setup. I want the turbo to sit in the stock location (IE: The location that the OEM GTi-R manifold puts it). This will allow me to use the GTi-R J-Pipe and downpipe which can be purchased for a reasonable price. I figure the less custom parts I have to have fabricated the less money I will have to spend. I’m not cheaping out (Which can be a bad idea on a turbo setup), I’m just trying not to reinvent the wheel.
The one tubular manifold that will put the turbo in the stock location is some Chinese made piece on ebay. Based on the experience of others, I’m willing to say that the $240 Ebay manifold is just as likely to crack as my modified GTi-R manifold. Someone in the SR20 community is also working with LoveFab to create a tubular FWD SR20DET manifold that will put the turbo in the stock location. I figure by the time the modified GTi-R manifold cracks (if it does) I can upgrade to that manifold once it is available.