Head Lifting at 1.8 bar of boost ~ 450hp
 

Hey Guys, which studs are and headgasket are you using at that power level ?

we do door 2 door racing with the cars and time attack.

engines are complete built bp engines.

Jan

I am not at that power level, and have no direct experience...

Supermiata HB studs

Yea I had the same issue but at 1.6bar but closer to 400whp not quite 450. I am going with the HB studs that are linked above, they allow more tq they are arp2000 instead of the standard head stud material.

Is head boss cracking a concern with the higher specified torque of the HB studs? I'm going to be installing mine soon and I'm nervous about taking them to 90ft-lb.... Supermiata was unfortunately not very helpful when I asked. Wondering if my understanding of fasteners is just lacking here, maybe forces are way different given the different stud material and dimensions? I'd like to avoid destroying a $2000 head before I even have the chance to fire the car up

I haven't had any issues with 90ftlb. Head is doing fine. I think you'll be ok

Use lots of the goo that comes with the studs.

Compressive forces do not break things.
Tensile stress and metal fatigue do.

I'd encourage all of you to do some serious reading about the torque specs included with various aftermarket head studs sold for the Miata.

It shouldn't take much searching to find some real world experiences

One thing that WILL crack a block, it torquing studs down into the block.
You never torque a bare bolt right down into a blind hole, it acts like a screw jack and cast iron does not like being stretched.

Studs go in finger tight, or just nipped up, until the bottom of the thread in the block is reached.
Plonk on your head, and then torque down the nuts to the specified figure.
Top of the block is in compression, stud in tension, head in compression.
If anything does go pop, its going to be the stud.

Yeah, I read that thread when I installed mine now that I look at it again. I went big washers, 3 steps, lots of the ARP lube, and 65ftlb.

I've read quite a bit, and used that information the last time I installed ARP head studs. My question was specifically about the HB studs as what SuperMiata recommends is substantially different than what the popular consensus seems to be on head stud torque. I'm sure there are some gaps in my understanding of fasteners, and was wondering if there is something else going on with the HB studs that might lend itself to a 90ft-lb torque spec being safe in our application. Different thread design, ARP2000 vs 8740, etc.

FWIW, just took a cheap caliper to each stud/bolt variant I have sitting around. Middle ARP studs were purchased about 3 years ago, HB studs purchased earlier this year. HB are ARP2000, the Miata studs are 8740
https://scontent.fapa1-1.fna.fbcdn.n...78&oe=600A6848

I just installed my new head on my block today. Supermiata HB studs to 90ftlb. No issues, I've used them before at 90ftlb on my other head and also had zero issues. Just use a lot of the ARP moly and it seems to be fine

So I lifted the chrysler studs last year.. moving onto bigger things for this next year

It might be worth checking your head for hardness.
If its ever run dry and been seriously overheated, the aluminium may have been annealed and become soft. That can make holding down head gaskets problematic, no matter how strong your studs.

Might be worth a shot trying this https://www.summitracing.com/parts/s...da/model/miata . Supposedly it can deal with very minor head lift and maintain seal.

Wow, that's interesting. I went with a oem MLS this time instead of the cometic MLS last time. Will see how it goes, I don't expect I'll have any issues at 25psi (hopefully)

Cometic HG (copper sprayed Permatex), sees about 25 psi quite often, ARP torqued to spec. No issues and not afraid to beat on it. I am afraid of turning the boost up any more with the 6MT though.

Nice, yea I've already broken one az6 earlier this year, 4th gear left the building. I think the reason my cometic wasn't sealing is my fault bc I didn't get the head surfaced when I built my engine 2 1/2 years ago. It was fine until I cranked the boost up.
https://cimg1.ibsrv.net/gimg/www.mia...8b63fb7d35.jpg
Block side of hg was fine
https://cimg3.ibsrv.net/gimg/www.mia...6a52d062a8.jpg
Head side of hg showed a different story.

I've run the felpro mls gasket at low to mid 30s psi and beat on car regularly with no issues. I do intend to build another motor for nitrous use on top of that boost level and will be using those cut ring head gaskets along with half filling the block. Will see how the sce cut ring gaskets perform upcoming year. They are a little pricey though.

That cut ring gasket is .055 thick.
I believe the compressed stock Mazda MLS is .040-.045 thick.
It MAY be stronger but it will definitely reduce quench which is a BAD thing in my book...
Quench should be IMPROVED, not reduced in any application that will run pump gas.
If you're specifically running heavy fuel it doesn't matter.
E85, methanol, 110+ race gas are not nearly as critical regarding detonation.

Now, If anyone can find a cut ring gasket that is as thin or thinner than the stock MLS that would be the ticket...
The .055 gasket would work fine with the block "decked" .010-.015

I spoke too soon I think. When I was torqueing the nuts the #4 cylinder passenger corner stud made a cracking sound as I was passing ~80ftlb. I then went and torqued it to 90ftlb but it did require more turns than I thought it should. Didn't think a lot of it, car ran and started fine. Drove it 20 miles it was fine, didn't really boost it that day. Yesterday I went and did some virtual dyno pulls, before I even did a pull I noticed on startup that the car had a slight misfire that went away, little smoke came from the exhaust, I went home and picked up my laptop and when I started the car the same thing happened. Then as I was driving the car and came to a stoplight the car started to sound like a Subaru and white smoke was pouring from the exhaust. Once moving the smoke kinda goes away and drives fine, but at idle it's messed up. Pretty sure I cracked the head in the corner and it's leaking coolant into the cylinder. I pulled all the plugs and they looked ok, the #4 cylinder and #3 looked kinda wet. I pulled the VC and pulled the stud shined a light down there and didn't see anything, but something is definitely wrong. It's odd because on startup the car seems ok, then once it warms up it gets progressively worse. I'm gonna have to pull the head, and luckily I have a spare head I may end up using and pulling all the new springs/retainers I just bought and transferring it over. Pretty disappointed, and I can say I would not recommend 90ftlb now.

People should listen to EO2K

soo basically you didn’t confirm it cracked the head and are saying it did.

Any real info like it’s consuming coolant or it has intermix of fluids? Or a visual check at the boss area? Sounds like conjecture at this point.

I think people in this thread are well beyond the realm of stock power output and know that “miatas don’t lift the head” is in fact a false and dated.

Threads from 10 years ago when arp was specing wrong washers shouldn’t be mentioned in here.

Pretty sure I said I didn't pull the head yet, it's consuming coolant, and I did pull the VC and the stud and have a look at the stud boss and didn't see anything. There is no mixing of fluids but it's eating coolant. I'm making an educated guess and yea I wouldn't recommend this much tq, because I never had this particular issue previously at lower 70ftlb. I'll know more when I pull the head but life and a job makes that difficult at the moment.

Our reply to the same question you asked in this thread:

"Hi Nick,
On our engine builds we use the recommended value which would be included in the box. On our HB head studs that's 90 ft lbs.
That said, we have seen the same reports you have regarding head cracking. Not something we've experienced. Ultimately that will be between you and your engine builder if you want to use the recommended value or go with something lower.
Ed"

It sounds like you wanted from us, a definitive guarantee that your head would not crack. Of course we can't offer that. There isn't a lot of data for 30+psi, HB studs and 90 lbs torque. Our experience has been positive. Others have reported cracking heads with thinner studs and lower torque values.
We're all in uncharted territory here. Our message is that lacking a definitive scientific answer, it's up to each person to weigh the risks of modifying their BP to quadruple stock power. We can't offer you a cut and dried yes/no answer. Just share our experience and let you decide what's best for your project.