bahurd

iTrader: (8)

The pic you showed of the cracked downpipe also showed the replacement cast manifold. I can assure you the location of the v-band flange is not in exactly the same spot as the MK manifold so you can’t blame Lars “skills” or “welds” on the cracks in the downpipe.

Even a minimal change in mating location or angle will put stress into the downpipe causing it to crack wherever the stress (and heat) is greatest.

So now you’ll need to have a downpipe “fabricated” to match the cast manifold and everything will be good again.

ragtag93

Appreciate the copper anti seize tip.
Engine mounts are stock and agree that engine moves more than it should. I've only cracked manifolds and downpipes on the track, which makes me think the Gs don't help.
The tune started out as a 1.6 MS basemap with some additional street runs using tunerstudio tune analyze feature. Advance is set to 4 degrees (from basemap) with 100% ethanol content. Agree that it could use a better tune, but AFR seemed stable and didn't see any issues on the logs. I'm not sure what a tuner could do different to help with EGTs. I always assumed running on the track for 1+h is just a different level of heat than any street driving.
Agree that mani location is probably shifted slightly and the plan is as you said, to refab the downpipe to fit it better. If it's due to movement though, I'm still thinking it will crack. I'll post when I have an update.
If you read my 1st post, the whole reason for switching to cast mani is b/c original welded MK miata one kept cracking at the welds. I've told Lars that the cast one seems to hold up better. Every time I email Lars he does not seem to have the manifold or the downpipe in stock - that's the frustration.
Either way, there r plenty of posts about cracked downpipes, even w/ the FM kit before they went with a cast piece:
I just cracked my FM Downpipe, Suggestions please - MX-5 Miata Forum

sixshooter

iTrader: (12)

I stopped reading at engine mounts are stock. Don't throw rocks at a vendor for your mistakes. Not cool.

Newaza

If I read your post #18 correct you said you added a flex joint and a custom hard bracket to solid brace the downpipe to the transmission, with the brace being between the turbo and flex joint? Try placing the flex joint between any solid exhaust bracing and turbo to see if that helps. Maybe after the first downward bend after the turbo if there is room. Combine that with stiffer motor mounts may be the ticket.

Also what is your timing like when on e85 at 10 psi? excessively retarded timing and/or too lean mixtures can put a lot of additional heat in exhaust.

ragtag93

Thx for the feedback. Yes, will try adding a bracket just after the flex joint. There is only one exhaust hanger roughly where the trans ends. It allows it to move a lot, so extra bracing can't hurt. Adding my timing and flex sensor pic:

Newaza

In my opinion any bracing between the turbo outlet and flex joint maybe should be removed. That will help alleviate stress in the hottest parts of the downpipe as it expands from heat. That will also help with the stress from engine movement and vibrations as well I would think.

Might want to also look to what some others on here are successfully running in so far as timing when on e85 with a similar setup to you and tracking there car as well.

I would post one of my spark maps but mine is a very different animal from yours and used for a very different purpose.