I may be a n00b, but I'd venture to say a restrictive catalyst 8" from the outlet of the turbo would be slightly detrimental to performance. If not purely from the reduced air flow, then perhaps the extra weight hanging off aforementioned failure zones AND additional thermal mass radiating directly towards the area in question known for failures due to thermally induced stress fatigue and fastener loosening due to CTE mismatched mating parts.

And def no benefits of a catalyst free system. They call them race pipes because they are loud and fucking cool, not because they increase exhaust velocities and lower EGTs. I may or may not be a mechanical engineer with experience in high heat thermodynamic systems, but I did stay at a Holiday in Express last night.

Jumping back to the original post, any thoughts on a FM kit with their locking hardware and exhaust brace?

It does not fix studs stretching problem between manifold and downpipe.

what locking hardware?

This item

Which they say

And Savington/TSE has their Inconel kit, which states

So, to make sure I'm understanding this correctly, as Shuiend says, even if things are locked down tight, the expansion/retraction of the stud itself will still occur, which can't be solved with additional hardware.

Is this a particular pandemic to Miatas b/c of their engine vibrations/cornering forces?

The material in the head and the material of the bolt see different expansion and contraction rates. The standard M8 bolts see the actual stud stretching

Here is the original thread that we first discussed the issue. You can read there if you want all the details.

If you want a track reliable setup you either need the TSE Inconel Studs, or a V-Band setup. So whatever manifold you decide to go with, make sure it works with either of the 2 things mentioned above.

Awesome. Thanks

We aren't talking about the head/manifold junction

As for the FM kit, well they sell their stage 8 kit in M10 and clearly state these are if you intend to drill out and retap your manifold to M10x1.5. Its a 1mm difference so I don't have any issues with doing it

http://www.flyinmiata.com/index.php?...umber=36-00010


As for the root cause of the issue...that seems to be more pronounced with cast manifolds.

1) Cast manifolds are heavier, retain more heat, and most kits put the turbo very close to the head. This all translates to much more heat at the turbo/manifold junction, more heat, more expansion. SST tubular manifolds for comparison tend to have longer runners and their thin-wall tube design dumps heat much faster. Just a few inches of thin wall tube can easily dump a few hundred degrees

2) Material mis-match. Standard SST fasteners usually are 300 series..which expands 30-40% much per degree compared to iron. On the ramp up they will just expand right out of the flange side..on the ramp down, since they will cool faster and contract more per degree..as every thing starts to contract the SST stud will get stretched waiting for the iron to return to its original size. On the flip side..Inconels CTE nearly matches that of Iron. So if you have an Iron mani, inconel stud, and iron hot side, they will all expand and contract together.

3) Track abuse. Take the issue above and mix in constant thermal cycling AND a big fat heavy exhaust hanging off the turbo, and now you've got a real PITA. You have a source to torque, stretch, and fatigue small fasteners that see a great reduction in mechanical strength properties at high temperatures and everything has more freedom if it has come loose. This is where you have the potential for complete stud failure. This is another pro for inconel, as it retains its mechanical strength properties at higher temps compared to other steels

I ended up snagging the local FM kit. I plan to re-tap it M10, install inconel studs, install locking nuts (unless I can sorce inconel nuts), and brace/support my fat bastard downpipe.

That and I'll start with a much more conservative low boost map for the track to see how it fairs. If I break it..im going rotrex..absurdflow..or LSjuan :laugh:

Our inconel stud kit includes M10 Stage 8 locking nuts; inconel nuts are not necessary and will be prohibitively expensive if you can even find a source.

Yeah I plan to pick up your kit if I cant source anything through my OEM channels

Long, tubular manifolds have proved to have just as much of a problem with this issue, unfortunately.

Actually, I had FM install 10mm studs on the last manifold I ordered from them before they shipped it to me. So far so good...and that was 2 years ago. While I'm not a trackrat, I've done a few HPDEs with absolutely no problems. I would imagine you can request FM to drill the mani out for you or do it yourself, either way, there is enough room with their mani to go to 10mm hardware. I also know the newer FM mani doesn't allow the studs to contact the exhaust gasses directly like the older FM/BEGi manifolds did....which caused numerous problems for me when I had one of the older manis.

I'm running an FM cast manifold drilled to 10mm to take TSE studs combined with a Garrett T28 and BEGI Divorced stainless downpipe. It's performed faultlessly after a huge amount of abuse on the track at 270whp.

Before this solution my studs were backing out in approx 15 mins with 8mm standard hardware. It's well worth the money for those who can't afford the Absurdflow stuff.

Well it is good to know that the FM manifold can be drilled out and will fit the TSE studs.

I already have my M10 tap and 8.5mm clearance bit so I'll let you know how it goes. But from the looks of it there is plenty of meat around the threaded areas so the slight change in OD should be negligible