MY view on head studs for the MZR

[Realgib3]

Alright I'm copying this over from the original, extremely beneficial Lets Talk About Head Studs thread. That thread, great as it was, is now insanely long, dated, and recently filled with garbage. Please feel free to go back and read through it though, as some of what I'm about to post, definitely came from info/research/testing/etc in that thread.

So here we go, my personal view on head studs and head lifting issue on the MZR...

Originally Posted by KevinK2 Head lift, by my definition, is any condition where the compressive force at the gasket sealing embossments is not high enough to maintain a seal there. .

This is really the ONLY thing that matters. No engineering theory needed.

Almost everyone here (including myself at one point) thinks that head lifting happens when a bolt/stud actually stretches under high cyl pressure, allowing the gasket seal to break and water/oil to be pushed. The fact of the matter is, this may have happen to one or two people ever and that's even a stretch because this almost always only happens with major detonation.

What really happens in 99% of cases is just not enough clamping force, allowing high cyl pressure to push through the sealed surface. This clamping force is really the ONLY thing we should be looking at... So let's look at it...

Disclaimer: I am just going to be using these numbers for the sake of having round numbers to work with. If you start disputing them, I will lose my shit. The tq numbers are calculated as % change from my baseline (stock). The whp numbers associated will them take into account the average whp most tunes would get out of the calculated tq number on this engine with our current rpm limits. Also, these are all on the conservative side.

All specs below will be using ARP Ultra Tq lube.

UTS Values

-OEM Bolts- 150ksi

-ARP2000- 200ksi

-H11/L19- 240-260ksi
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-Stock Head Bolts -
- OEM Tq + angle = 65-70lbs
- 65-70lbs = 620whp/500wtq

10mm ARP2000
-ARP Tq spec = 60lbs
60lbs = ~8% LESS than stock = 575whp/460wtq

10mm H11/L19
-ARP Tq spec = 80lbs
-80lbs = 18.75% more than stock = ~775whp/600wtq

11mm ARP2000
-ARP Tq spec = 80lbs
-80lbs = 18.75% more than stock = ~775whp/600wtq

11mm H11/L19
-ARP Tq spec = 95lbs
-95lbs = 31.6% more than stock = ~850whp/660wtq


12mm ARP2000 (Nissan Pulsar gti-r)
-ARP Tq spec = 100lbs
-100lbs = 31.6% more than stock = ~875whp/685wtq

1/2" ARP2000 (Nissan Pulsar gti-r)
-ARP Tq spec = 110lbs
-100lbs = 41% more than stock = ~900whp/710wtq

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Now....... that actually lines up very very well with what I have personally seen in a real world environment.

That is also all using ARP's very conservative tq specs which have been known to be measured closer to 65% yield on the fastener, not the 75% yield ARP publishes. Either way though, this means we can and SHOULD apply more tq to the studs. Since 85% of yield would still be plenty safe and get us much more clamping load, lets add 15% more tq to each stud. This would put us at 90% yield if ARP's initial 75% number was true and 80% yield if the number is closer to the 65% value that has been measured (evom has a lot of good info on this). Also note, ARP (though you'll get a dif answer every time) has consistently told people "It's fine to go 12-15% over if you want".

So lets redo it all with that in mind...

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10mm ARP2000
-ARP Tq spec + 15% = ~70lbs
70lbs = ~7% more than stock = 675whp/535wtq

10mm H11/L19
-ARP Tq spec + 15% = 92lbs
-92lbs = 29% more than stock = ~840whp/650wtq

11mm ARP2000
-ARP Tq spec + 15% = 92lbs
-92lbs = 29% more than stock = ~840whp/650wtq

11mm H11/L19
-ARP Tq spec + 15% = 109lbs
-109lbs = 31.6% more than stock = ~950whp/740wtq


12mm ARP2000 (Nissan Pulsar gti-r)
-ARP Tq spec + 15%= 115bs
-115lbs = 31.6% more than stock = ~1000whp/770wtq

1/2" ARP2000 (Nissan Pulsar gti-r)
-ARP Tq spec + 15% = 126lbs
-126lbs = 41% more than stock = ~1150+whp/830wtq

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Now these numbers are alllllllll obviously approximations, but they are all based on more head stud research and real-world test results than most, if not all others in this thread have seen, so take from it what you want.

[tastysi2004]

thanks for this!!!! @2.0t03speed; time to get those high hp eh'?

[Easter Bunny]

Nice summary

But the stock bolts are 150.00000000000001 ksi

[aviator79]

Originally Posted by Easter Bunny Nice summary But the stock bolts are 150.00000000000001 ksi

Thats what I measured when I used that machine to shear one.

But they feel like take 300+lb ft to remove. I assume this was in the other thread but are the head studs torqued to spec just as hard to remove after 10k miles on a engine not assembled by mazda? IDK, have not taken head off a built engine. Normal or ? torqued higher at factory?....I can delete this post to keep thread clean.

I wish I could go test these bolts on the machine I am talking about. Has anyone done that? They have them at colleges that someone on here could use. FIT has one so others must.

[KevinK2]

Pablo tested stock bolt:

TS = 160 ksi
YS = 130 ksi (.2%)
e == 65% elongation (.65" from 1") This high value may reflect it's torque-to-yield use, and reuse.

OEM Bolt Test Results

I feel this minor difference does not change the excellent summary by Realgib3.


.

[Airman3454]

So with a 500WHP setup playing with the ARP's is just a matter of time until it becomes a bigger issue?

Sounds like I will be better off replacing the ARP's with the L19's since my block is still in the engine stand.

Thoughts?

[Realgib3]

Originally Posted by Airman3454 So with a 500WHP setup playing with the ARP's is just a matter of time until it becomes a bigger issue? Sounds like I will be better off replacing the ARP's with the L19's since my block is still in the engine stand. Thoughts?

Standard ARP's at 70lbs should support >600whp for a long time.

With that said, I would just spend the extra $100 and get l19's but that's just me

[Airman3454]

Originally Posted by Realgib3 Standard ARP's at 70lbs should support >600whp for a long time. With that said, I would just spend the extra $100 and get l19's but that's just me

Yeah I might as well since the block is pulled anyways. Thanks dude

[Fstrnyou]

Thread revival, because I think it's relevant to anyone trying to figure out what head studs to use...like myself.

ARP Custom Age 625+ is another option.

Cheaper than H11/L19 and same/similar strength.

[mituc]

I have these in the current engine. You can torque them to stock values (70lbs) for a 600ish whp build or torque them to 80lbs for 750+.