Miata Turbo Forum - Boost cars, acquire cats.

Quote:

Originally Posted by nitrodann (Post 1414569)

Hi,

I know that many many Miatas have difficulty keeping manifolds together under intense road racing use, and on 2 dedicated racecars I have had a similar manifold failure at the collector.

In both cases the collectors are extremely heat effected and very very brittle, infact you can see in the following picture how crystalline the structure has become where the manifold has torn. This particular manifold didnt have as much penetration as would be ideal which is my fault, however just like the other one it tore right through the steampipe, it wasnt simply a weld failure, or perhaps I am wrong, educate me.

Can anyone give some feedback, advice, or share their own experience?

https://cimg6.ibsrv.net/gimg/www.mia...bd975fa51c.jpg

Thanks,

Dann

Hey everyone:)

I registered here just to post on this thread. I too had a hard time when deciding what to make my manifolds out of. I narrowed it down to 321 sch40 or MS sch40. In the end cost wasn't a factor for me as the 321 steam pipe isn't too bad. At the end of the day I chose mild steel steam pipe sch40 for the runners and mild steel for the head flanges. The v-band flange at the turbine came from full race and its 304ss. The w/g flange from tial is 304 as well I think. Anyhow I chose the steam pipe because after much research I just couldn't find the instances of them failing like the 304. 321ss has too much expansion for my design I think and that's a whole other subject. I used er70s2 for all the MS to MS welds, and 308l for the 304 to MS welds. EVERY single weld was back-purged with 100% argon. EVERY single weld was 110% pen. I did this by running a root gap, bevel, and ran a key-hole when welding so that I wound up with beads on the inside of the joints. During construction I fully ported the insides leaving the quality as good or better than a casting, completely smooth and pit/crack/gouge etc. free. No sharp edges, not too much heat input, no undercut roots, etc. All it takes is one small spot for a crack to propagate and even the best material won't save you. I see in the OP's post that the penetration was less than optimal in one of the hottest and most stressed spots on the manifold. Please excuse me if this isn't Miata related however it is subject matter related and there just isn't enough info out there on the subject of MS turbo manifolds IMO. I am pushing around 12 lbs of boost now for 6k miles and no issues whatsoever except the White lightning substrate melting through a bit which Swain says is perfectly normal. I can tell you, the stuff works. I am starting tuning now and these manifolds are going to be severely punished so I would be happy to let you all know how they hold up.

Best,