MY view on Head Studs for the MZR

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
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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.

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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.

 

Man, I REALLY appreciate all of the knowledge-dropping here on MSO, @Realgib3 ! This will help me decide the best route to go when I get built with 4032s/go EFR 7163. Honestly, for me, looks like:

-Stock Head Bolts -
- OEM Tq + angle = 65-70lbs
- 65-70lbs = 620whp/500wtq

would be all that's needed...

 

Personally tell people go stock bolts unless going over 450tq. Stock bolts also do not require a re-tq procedure, which I would advise for any stud.

 

Yeah, 500whp shouldn't eclipse 450 wtq. But I'm confused: even though they don't require it, are you recommending re-torquing stock studs? Maybe I'm misreading your statement...

 

Nope, to clear things up, stock hardware are TTY Head BOLTS, that do not need to be re-torqued. Everything else is a head STUD and does require the re-torque.

 

Yeah, that's what confused me. Stock head studs are tq + degrees turned afterwards. Your comment made me think you were saying to go even beyond that, LOL.

Anywho, think stock would be solid/reliable for 500/450 @ the wheels? I'm thinking so...

 

Awesome info, thanks for posting. Is there really that much distortion in the stock block even with a closed deck design? Where is your source info on this?

 

>1150+ whp

 

Regarding distortion, I always heard our blocks distort so little that machining plates like this, for instance, aren't even needed when boring/honing:
http://www.ebay.com/itm/Massive-Abs...0-2-3-Mazdaspeed-3-6-Miata-MX-5-/261035242373
The explanation was that our head studs anchor so deeply into the block that distortion is all but non-existent. I saw lots of knowledgeable folks on the other forum forego using a block plate in the machining phase of their builds, saying it's unnecessary.

Hate doing it (other forum link), but @Realgib3 determined they're not necessary already here:
http://www.mazdaspeedforums.org/forum/f106/gi-torque-honing-plate-142085/index3.html

Did something change or accumulation of more data render it a good idea? Maybe it's if you're boring out the sleeves to 88 or more that they're needed?

 

Nope, you're correct, we're just talking about two different things.

It is true, when testing distortion of the cylinders from a TQ plate, it showed that cylinders did not distort much at all, making it unnecessary to use a plate when boring/honing.

What I'm talking about here is the distortion of the cylinders under heavy load/cylinder pressure. More or less, the cylinders are "flexing" under extreme stress and causing a break in the seal of the head gasket. If you look at any of the very big power guys still on 10mm head studs, you'll notice they're also sleeved and are thus able to keep gaskets happy for a lot longer. From the factory, we have something like a 2mm sleeve, which is almost nothing, then most go to 88mm to get their cylinders round again and now you're down to only 1.5mm of iron trying not to flex at all under crazy stresses.

 

So what do you recommend on a 500/450 setup with stock headstuds, H-beam rods, and 4032 pistons? Upgrade the headstuds?

 

IMO, keep it simple for that power level.

Manley H-Beams with standard rod Bolts
Manley Pistons 88mm
OE Rod and Main Bearings
OE Head Bolts
OE Head Gasket

 

Thx for the input. I have my heart set on the 4032s because of their service life. These:
http://www.speedperf6rmanc3.com/products/sp63-4032-series-pistons-for-mazda-mzr-disi.html

SP63 assured me they'd be more than up to the task of 500whp/auto-x/tracking. They're confident in their hard anodized dome. Things are going to be nice and cool too because I'll be running a crapton of methanol for my extra fueling, and a failsafe just in case it stops spraying for whatever reason (I can hook it up to the failsafe trigger to open my BPV on my Guardian Angel v2 too).

 

Understood, and I do get the theoretical reasons you'd want to go with a 4032. The only thing I will say is I challenge anyone to show me a 2618 pistons, in a properly machined MZR that has any piston slap whatsoever... Along with that, you will easily get 50k+ miles at that power level on the Manleys. I think @Sho is over 50k on his Manley's at this point, for instance, and he's well past that power level.

 

Yep. ~53k on my build so far.
Manley platinum series 88mm, Manley h beams oem hg, oem head bolts.

No piston slap at all. And the car up until I retired it from daily driving 2 weeks ago, had all that mileage put on it in 13 months, with 10-15 start ups and shut downs per day.

Last comp test resulted in this.

 

53k in a year? That's crazy.

 

Bought the car with 25k miles in August 2012. It now has 215k lol

 

I feel like piston life will vary greatly on usage anyway. If you're flogging on it constantly I could see them having a short lifespan but if you're just going WOT once or twice a day and a few mid boost pulls then you'll be able to get a long life out of them.

 

Sho drives the shit outa his car lol. I know because it gave me ulcers back when he was doing on this on a 120k+ miles stock block.

Piston life and engine compression vary mostly due to machine work and assembly.

 

IIRC, you guys said no pinned cams or keyed crank either, right? I don't think SP63 even does those services on their Stage 1 long blocks, but I could be wrong... Looks like they don't, though: http://www.speedperf6rmanc3.com/products/sp63-stage-1-built-long-block-for-mazda-mzr-disi.html