Alright I'm copying this over from the original, extremely beneficial http://www.mazdaspeedforums.org/forum/f106/lets-talk-about-head-studs-135380/ 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...
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
-----------------------------------------------------------------------------------------------------
-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
-----------------------------------------------------------------------------------------------------------------------------------------
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...
-----------------------------------------------------------------------------------------------------------------------------------
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
-------------------------------------------------------------------------------------------------------------------------------------------------------
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.
-----------------------------------------------------------------------------------------------
Now after more testing and results, I just need to put out the disclaimer that I still stand by all my feelings on this topic, HOWEVER, I also believe that at a the power level that IMO Needs a 12mm+ head stud, the lack of rigidity with a stock sleeved block is also a huge cause for the head gasket issues that many have seen.
This means, if I was building a high hp disi again, I would be sleeving the engine or half-filling it with Hardblock to keep the distortion in the deck surface around the combustion chamber to an absolute minimum. With the stock sleeves, especially on an 88mm bore, I believe that distortion is significant enough under heavy stress to upset the sealing surface and aid in causing HG failures, no matter which studs are used.
Lastly, also after more testing and experience I would absolutely suggest re-torquing any of these head studs you would go with. It's not hard at all to get the cams out, in the car, to get to the studs, so there's really no excuse not to do it. With the amount of variance I've seen in TQ numbers after going through this procedure, I would tell everyone with a built motor that it's a must.
So here we go, my personal view on head studs and head lifting issue on the MZR...
KevinK2;2635511 said:
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
-----------------------------------------------------------------------------------------------------
-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
-----------------------------------------------------------------------------------------------------------------------------------------
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...
-----------------------------------------------------------------------------------------------------------------------------------
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
-------------------------------------------------------------------------------------------------------------------------------------------------------
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.
-----------------------------------------------------------------------------------------------
Now after more testing and results, I just need to put out the disclaimer that I still stand by all my feelings on this topic, HOWEVER, I also believe that at a the power level that IMO Needs a 12mm+ head stud, the lack of rigidity with a stock sleeved block is also a huge cause for the head gasket issues that many have seen.
This means, if I was building a high hp disi again, I would be sleeving the engine or half-filling it with Hardblock to keep the distortion in the deck surface around the combustion chamber to an absolute minimum. With the stock sleeves, especially on an 88mm bore, I believe that distortion is significant enough under heavy stress to upset the sealing surface and aid in causing HG failures, no matter which studs are used.
Lastly, also after more testing and experience I would absolutely suggest re-torquing any of these head studs you would go with. It's not hard at all to get the cams out, in the car, to get to the studs, so there's really no excuse not to do it. With the amount of variance I've seen in TQ numbers after going through this procedure, I would tell everyone with a built motor that it's a must.
