ARP head stud torque for a Miata.
 

Searching yields wildly different answers. I do know some are really wrong.

Facts.
1) The factory head bolts specs are 56-60 ft-lbs.
2) ARP head studs have finer threads and the nut is lubricated with ARP Molly.
3) Using the same torque value as factory bolts will result in significantly more than factory clamping force due to the design of the studs.
4) As far as I can tell ARP studs are 11mm and 190,000 PSI tensile strength studs.
5) The box they come in recommends 71 ft-lbs for that size stud “to achive Optimum clamping preload (Clamping Force)
6) I have tightened them to the 10mm spec of 48 ft-lbs in the past and it has never resulted in a problem even at 300hp levels.
7) I have tightened them tighter based on internet info and destroyed a head with $2000 worth of port work on it by smashing the bosses and cracking it. I can’t remember what that torqe was but it wasn’t much more than 71 ft-lbs if any.

My guess is somewhere below factory torqe spec is what you wan’t with ARP hardware. My guess is they will still clamp harder than stock and you really don’t want to go with much more clamp than stock. So what is the spec? my guess is 48-50 ft-lbs. What is everybody else doing?

PS. I actually think the ARP head and main studs are solving a problem that simply doesn’t exist on a Miata but I have them anyway. About the only thing I think they could be doing is providing more consistent clamp force at each stud than stock.

Bob

Have you measured your used gaskets?
Turboford.org had dedicated threads discussing this with iron and alloy heads. The stock Ford 'bolt' specs were too high with studs (IIRC).
Way too much and you collapse the heads around the studs. Too little and, well, blown out h-gaskets as well.
Alloy heads on iron blocks can be a problem. Differing expansion rates can smash the gaskets around the studs/bolts. Even clamping is what is wanted. The head's RA is also a factor.

Measure your used h-gaskets around the studs and in-between. Need to keep records of the torque used also. The most even without failure, such as the fire-ring moving, is what we're after. Sorry I don't have any numbers for you, just suggestions.
BTW, I'm drunk-posting, so this may not even make sense to me in the morning... Editing 'cause I've had way too much, and it's getting hard to type, and I know i've left stuff out...

I purchased my studs from Flyin Miata, and they had a correction in the instructions to torque them in the 50 ft lb range.

I would agree that Miatas are not notorious head gasket blowers. I would never have a race motor without them however.

As far as clamping force, I was under the assumption that studs were supposed to clamp harder than stock, but to maintain the integrity of the block threads. Race motors have the head on and off frequently, and head studs make parts last longer.

I clamped mine to 65 ft*lbs and didn't have an issue, but I also wasn't pushing even 200 hp. When I pulled the head off, the gasket wasn't crushed oddly or anything and it hadn't leaked. Just my experience. But as you pointed out, the head studs don't do a whole lot on our closed deck blocks. Their main function is simply being reusable. On open deck blocks like Hondas, they are absolutely essential. On my old civic, I was getting head lift and popped a HG at 7 lbs. ARP studs torqued to 75 ft*lbs and never happened again. Thats also an open deck, alloy head and block.

Its been a long time, but I seem to recall the instructions stating 50ft/lb with the ARP lube, and 65 ft/lb with engine oil, but don't use engine oil if at all possible. Would probably be best to call ARP.

I've never seen those instructions in like 4 boxes of Miata head studs I have had for various engines I have put heads on. I do know that the generic 71 ft-lbs listed on the box for 11mm studs is dangerously close to destroying a Miata head by crushing and splitting the aluminum bosses in the head they clamp down on. Miata head studs are significantly oversize for the amount of clamp force needed.

Bob

Sounds about right. Strangely I have an old email from Bill at FM stating 71 ft-lbs but I swear I remember they told me 48 before as well. You can also find people claiming 85 by searching. So there is a tone of confusion on this.

I now know the torque level on a Miata needs to be much less than the capability of the stud.

Bob

Holly shit I torqued them to 80 ft/lb!!!! :noob:

71lb here, I'll go lighter next time..

Holy shit so 50ish is fine??

The workshop manual is 60 on stock bolts

youre lucky you did not crack your head.

Shit Im lucky it ran for so long then. Lol.

It doesn't make sense to me that a stud that by it's design (Finer thread on super hard high strength I quality steel threads and well lubricated) should produce significantly more clamp force at a given torque level should be torqued any higher than stock. and most likely should be less.

Miatas don’t suffer from heads not being torqed tight enough. I can't see any reason to more than double the clamp force at the risk of crushing the head.

http://www.flyinmiata.com/projects/c...ts.php?UID=789

Note the picture. Stock bolts at stock torque don’t even hardly leave a scratch mark on the bosses.

Bob

Well shit. This all would have been good to know 7 months ago. I cant remember what torque spec I used on mine but it was sure as hell more than 50. I did not use the lube the last time I assembled my engine, just engine oil.

Oh well, working fine with no cracks (that I know of) so far.

After much thought on this subject, I opted out of studs for my GTX engine build and after reading this i'm glad I did.

I am thinking the stock bolts are softer so they stretch more requiring a higher tq to ensure correct clamping force on the head/gasket whereas the arp studs are stronger resulting in less stretch therefore needing less tq to achieve the same clamping force on the head/gasket.

lol oh well i did my ARP studs like 5 months ago with the lube and at 65lbs

Reguardless of the strength of steel all steels have really really close to the same elastic modulus so unless they are a different diameter then they are the same stiffness as long as you stay below yield. And the fact is the head will yeald under the washers before the bolts will and I think this is true even with the factory bolts. The factory bolts will require a lot higher torqe to generate that much clamp force though and they might twist before they generate as much clamp.

Bob

Curious how you arived at the 65lb torque level? was it documented somwhere?

Bob

Way too much conjecture and guessing in this thread for me. I followed the instructions that came in the box and I've had no problems at all.