Is 90ftlb for Supermiata head studs too much? Cracked head
 

So for those of you that are following my build thread will already know. But I cracked a head with the Supermiata HB head studs. They say to go for 90ftlb and well.... Watch the video to see what happens when you go that high. Now, a little disclaimer I'm not saying you will crack your head going this high, I did my old head at 90ftlb and it was fine, this one was not. Probably can chalk they up to casting irregularities between heads. Some might be fine some might not be. Personally I will not be going any higher than 70ftlb when I install my spare head. Before you ask, yes I used moly lube, cleaned and chased the threads in the block, used the correct washers, and went in the correct tq sequence 30ftlb/60/90 in 3 steps. I have done 7 or 8 head installs on Miatas and yea I've never cracked a head until now. Curious to see what SM thinks about this. And I wanted to warn any of you that are planning on using their high boost studs.

When the head cracked I was in denial and didnt want to believe it, so I went ahead and buttoned the car up and it was ok for the first 20 miles or so before it started to idle like a subaru and blow a ton of smoke out. I had a guy comment on my YT channel that he too cracked a head on the EXACT same stud so this isnt the first time someone has had this happen. Shitty head or too much tq? You tell me.

Which style washer did you have? There were a few threads round these here parts that stated the 90ftlbs was pretty smoothbrain for the run of small diameter washers.

SM instructions should probably stand to mention that little caveat since it was likely through history they sold both revisions of hardware.

I used the washers that came with the kit from them, they are bigger than the old washers and about the same size as a OEM washer.

Cool so at least you didn't get bitten by that issue, though it doesn't really help your current situation any. :(

yea, it does suck but at least i have a spare head I can transfer the parts over to. It took me 3 days to get over it lol....the mourning process.

Nicely-done video. I feel your pain and hope you can rectify things without too much trouble.

haha thanks brother, yea it shouldnt be too bad to fix. Just have to wait on the machine shop and I think Im gonna run a SCE Vulcan Split ring HG this time, that should hold my 22psi easily.

It's a huge bummer man. When putting my motor together I did a bunch of research on this, and IIRC settled on 70 ftlbs with the ARP stuff being safe. Lots of folks torquing to 80-90 without issue, but also I've read of cracked heads from this too. I want to say it was a post from Savington that swayed me to not torque them to the ARP hardware recommended spec.

Now I'm paranoid! I just finished putting my engine back together. I did a bunch of research and landed on 70 ft-lbs using ARP hardware. I've only started the engine up a few times (chasing leaks) so it hasn't been stress-tested yet. Was I too conservative on the torque settings?

No 70ftlb is good. That's what I'm gonna go with this time. I am running the hb head studs that are asking for 90ftlb instead of 65ftlb for the off the shelf ARP Miata studs.