My downpipe has cracked for a second time near the turbo flange.

I am debating whether I should try to find a new one (I should be able to use an off-the-shelf part from Greddy), or have it welded again.

I think the issue is partially that it's a track car, so this part of the downpipe experiences pretty extreme temperatures, and secondly that the downpipe doesn't have a flex joint.

If I was to have it welded again, is there anything I should consider so it doesn't crack again so soon?

Should I get a flex joint added to the downipe? That would probably make it easier to reinstall, in addition to being less prone to crack.

 

if you add a mount point to it like how the stock tt one is, it will help if not remove that problem entirely. the flex joint would be nice too but the mount is really what you need.

 

Flex joint is another point of failure in a track car.

I would add v-band flange on the 45 deg vertical section of the downpipe at the bottom of the firewall.

This will provide a "pivot" for thermal expansion and engine movement.

The v-band off the turbo should be welded with special care. A high nickel filler rod (inconel) will provide most durable high heat weld. Watch undercut, penetration and backpurge like a hawk and choose appropriately thick pipe for front of downpipe.

 

I believe the turbo he has, was a bolted outlet, which is probably more prone to cracking than a v band. Wouldn't be surprised it's a mild steel flange. If the pipe itself is stainless, probably 309 would be a reasonable rod.

Engine and diff mounts might be worth a check if it's cracked in a short period of time. Here, generally like to run a turbo support bracket too.

If you elect to run a flex joint, it must be lined. The bare braided wire type without the liner some places sell, will disintegrate internallly under rotary stress, the accordian type seem to be more ubiquitous these days....and you avoid getting stabbed by stray broken wire as a bonus!

 

It’s a three-bolt flange to the turbo.

The new Greddy downpipe comes with a flex joint.

I suspect they added one at some point due to cracking.

My engine mounts are solid metal.

The downpipe has a mounting point, I just have no idea where it’s supposed to attach or how.

Last time it was welded with a stick welder, which probably wasn’t great, but it didn’t break on the same place this time.

There’s a possibility this break was caused by hitting the downpipe on a curb, though the rear flange doesn’t show any sign of this.

 

Do you know the part number for the bracket?

 

looks like this guy, https://www.amayama.com/en/part/mazda/n3a140080a

 

You just need any bracket to attach the tail end of the down pipe to the side of the tranny. There is a location on the side of the tranny with bungs for this purpose. That will support the cantilevered weight of the downpipe during bumps. This will help with relieving exhaust manifold stress/cracking as well.

 

I did do a Google search and found the part, but it's NLA, of course, so I'll probably go with fabricating something, since the stock piece looks really heavy.

I suppose they wanted it super rigid for a reason, but my exhaust is (probably) lighter than the stock one.

If the welded back up, I wonder if should add some gussets.

 

That would have been quite tricky!

When we had the twins, did get a hairline crack near the flange, not through the weld, even with a support off the box (can't remember the brand, it was Japanese with a welded on, rather than bolted mount). I think the pipe grew enough on track to munt the mounting bolt. If you're going to do it, I'd probably look at an isolation mount to allow some degree of movement.

 

The bracket does not need to be super strong. Just enough to provide a consistent mounting point so the tail end isnt able to bounce and apply torque to the turbo system. My bracket uses a 5/16 rod welded to a simple flat bar mounting tab. The hardest part will be tacking the bracket in the correct location. I suggest doing this real time in the car. Fab the bracket, bolt it to the transmission, then tack to the downpipe. Pull the downpipe and fully weld. Reinstall.

 

Thanks, I will try something like that. One of these days I should get my own welder...