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?





Thanks,
Dann

 

Re-weld with Gussets/supports

 

Do you mean from the flange to the manifold runners?

And while this is an obvious thing to try, what I also want to know is if this is the same failure most miatas have, or if this is a flaw in my design, technique etc?

Dann

 

The last 2 I've seen crack, were from ARtech, and cracked in the same exact spot.
He re-welded and gusseted them. See 99mx5's thread for pics of one of the examples.

 

Pretty much what I expected.

Anyone else?

Dann

 

What material? Certain materials are more susceptible to cracking than others especially when hot. I tried 321SS this time around because it should be much more stable at the temps we see. 304 is somewhat garbage compared to 321 at egt temps.

 

we have had issues with "steam pipe" lately too...we figure the quality of the pipe itself (from China?) these days is lower. We have similar crystalizng.

 

The solution is a cast manifold. FM or Trackspeed.

 

The metal near the weld becomes hard/brittle when welded and is more susceptible to cracking than the material outside the heat affected zone. Using different filler metals helps with this for the weld and the area it fuzzes with, the right filler can make a big difference. Which would be best depends on what alloy you are welding with.

I'm not a weld engineer but from memory 304 changes crystal structure or something around 1100*F, and that makes it brittle. 321 is a better material in this regard. The highest stress in that part is near the weld or at the weld. In your case the filler is probably a higher alloy and could take the stress, the base metal could not. IMO the best solution to completely solve the problem is use a material that can handle the temperatures reliably. A second option would be a design change to attempt to move stress from one area to another.

 

You might very well be right but our manifolds were scaling as well, away from the welds. As my mechanic said (who has made manifolds for years) he has never seen them do that before....hence we think it may be a quality of material issue....Chinese steel is having issues in other industry/environments too.

Cast might be an option or solution but not as yet for 1600 fyi.

 

I'm 100% on board with it being a material failure, which could surely be a quality problem as well.

 

The material is mild steel, sched 40 buttweld fittings.

Dann

 

Why dont I hear about this happening everywhere? Is it a hardcore track car only issue?

Dann

 

yes

 

Also, what rod is everyone using?

Ive got ER70s-8, as far as my research tells me this is the standard rod for this material, I could choose a ER70s-02 or something with a little less deoxidisers, but to be honest I really dont know enough to make the decision either way and have been using what my welding supplies specialist recommends for the application.

Dann

 

FM sells cast 1.6 manifolds. I've put over 40 hrs. on it. Basically, if you're road racing, and you're not slow, you will need a cast manifold. I'm genuinely surprised people are still trying welded manifolds on road raced turbo miatas. It's a problem that has been solved.

 

Our manifold is 347SS cast for a reason

 

Of course,

However for steampipe.. which filler?

Dann

 

I used ER70S on my mild schedule 40 manifold. The weld seam of the pipe failed but my welds did not after a few track days and lots of street miles.

 

Look above: Dann is asking ER70S-8 vs ER70S-2

Wow on fitting splitting! PICS?