What's the secret to welding a v-band flange to a cast exhaust housing?
I have a Holset HE351 and it has a bulky and strange 4" outlet like this:

http://i54.photobucket.com/albums/g1...t/DSC00948.jpg

and I was thinking about turning it off flat like this:

http://i980.photobucket.com/albums/a...s/IMG_0131.jpg

and then plug the wastegate hole and weld a 3" v-band to the turbine outlet kinda like this:

http://alphatuning.com/wp-content/up...3/DSCN0174.jpg

 

I won't get into a filler rod discussion (aka fighting words) about what to weld it with, but preheating is a wise idea. There aren't any "secrets" really if you know how to weld. Preheat, make a pass, preheat, make a pass... You get the idea. The temperature you preheat to is also very debatable as well, but it helps to have a dedicated oven / grill / fluid heater / etc but a torch will work if you take care, it's just not as efficient.

They do make a no-preheat cast welding rod but I personally wouldn't use it in this situation. Some people might though... Also, it will make a difference if this turbine housing is used or brand new. Heat cycled cast parts can be just as much as a PITA as a dirty cast part.

 

i cant offer any advice but id like to see what others have to say as well.

 

i would sell that and get something you don't need to modify. that is the best choice imo.

i have welded v-bands to cast turbines and never had an issue. my process:

clean/grind/machine surface of turbine to be welded to bare metal.
preheat turbine housing on hot plate 1 hour max temp.
clamp v-band to heat sink to prevent warping.
remove turbine from hot plate.
weld outside of joint.
let air cool to cold.
remove heat sink.
preheat again on hot plate 1 hour.
remove from hot plate.
weld inside of joint.
let air cool to cold.

i have used 309L and never had any crack.

aaron

 

^^^this!!! 309L or 316L

 

I have some 309 filler. I'm more concerned with how long it will last in service than anything. It just seems that with the amount of temperature variance that a turbo sees and the difference in expansion rate between the two material, there might be a problem down the road.

 

well, the problem with that is this turbo can make near 500whp and I got it for $199. Unfortunately, there are no other options for exhaust housings. I can machine it flush for free. Worst case scenario is I just trill and tap some holes in it and make a bolt on flange like this guy did:

http://i980.photobucket.com/albums/a...s/IMG_0133.jpg

 

316 won't help.
309 or 312

 

so long as you preheat and allow the cast housing to cool properly, you will be fine...in the past, I have done between 3-5 passes

 

not that I am doubting you, but am wondering what it is about 316 that makes it incapable of giving a strong weld between the two materials?

 

Generally the higher the number the stronger it is in most cases. 309 is great for dis similar metals, 312 or supermissle works great for those too or as an all purpose. 316 will work sure, but you won't gain anything out of it. 316 is great to weld to 316 but that's really about it. 312 would be your go to rod as it's a better all purpose rod.
Don't get me wrong, 316 can and will work but it will have a higher chance of cracking.
So for this case i would use 309 or 312. i had this same question a few months back and researched the crap out of it and talked to many people that know a lot more about metallurgy than i ever could.

 

Thanks for that. I'm going to pick up some 312

 

If your weld is sound and you preheated before hand the weld itself won't break due to expansion or anything like that. However, I have found that the weld is considerably weaker in loading than it would be if it was a true stainless weld.

That said, you can help yourself out considerably by properly flexing and supporting the exhaust so that the weld doesn't get loaded up while you're driving around.

FYI, that goes for just about any part you make. If you're concerned about cracking due to loading/vibration, make the effort to support your load case and make sure you weld with proper filler and techniques and you're going to help minimize your failures.