This was quite a learning for myself and was pure luck I came across the information.
I had originally bought a set of ARP 218-4702 which are ARP2000 for my build.
As with any build you go ARP for that extra clamping force over OEM or so I thought anyway.
The MZR / Duratec engines only have 10mm size bolts / studs which when you are chasing power they are quite small, this is something I over looked.
I was randomly looking on Facebook on one of the Miata pages and noticed a post about ARP head studs and a few comments mentioning they are junk.
Why may you ask?
From what I have been reading anything north of 450whp it is advisable to upgrade the head studs to the Custom Age 625+ by Speed Perf6romanc3
The ARP2000 at the higher power levels just do not have enough clamping force to prevent the cylinder gases lifting / creeping past the gasket.
It could be due to higher timing will increase the cylinder pressure, so it’s very possible with a safe ignition map you can run more boost and get away with the ARP2000 with more power. 🤷♂️
There is information regarding you can torque the ARP2000 higher, as with ARP I’m sure they advertise a pretty safe torque to yield figure too.
You can view that here. http://www.mazdaspeedforums.org/forum/f658/my-view-head-studs-mzr-173212/
This may also be worth a read, it’s quite long.
The Mazdaspeed boys seem to to push serious power in some of their cars and the company Speed Perf6rmanc3 have come up with a PnP solution to keep that cylinder head where it should be.
For a long time the only head studs available for the MZR platform were the ARP2000’s. As more cars started to creep into the 450-500whp territory, people began to lift their heads which in some cases lead to catastrophic engine failure. We began to research this problem and found that the ultimate tensile strength (UTS) of the ARP2000 studs was 190 ksi. In order to increase this number we had to look into other materials that could do the job. We started with H11 which was strong (UTS of 262 ksi), reliable, and offered many pros over the previous option. We then moved on to ARP’s L19 material as it matched all of the qualities of H11 but at a cheaper price that we could pass on to the customer. We ordered 1000’s of these studs before asking ourselves if there was even more we could do to bring the very best product to the table.
Intoducing the Custom Age 625+ head studs from SPEED PERF6RMANC3. These studs have an even higher UTS (closer to the 280 ksi limit of the material) than our previous L19 offering and have the added benefit of better corrosion resistance. We also upgraded the nuts in our head stud package to a heat treated version which have a lower failure rate when paired with an equally heat treated stud.
So in conclusion if you want to push big big power and high boost without the worry of the head lifting or having head gasket problems I’d suggest going for some Custom Age 625+
Head on over to http://www.speedperf6rmanc3.com/products/speed-perf6rmanc3-ca-625-head-studs-for-mazda-mzr-disi.html to purchase your set.
* TIP Don’t look at the price, just order them.