Ok, lets do a few measurements to assist anyone going down this path...
OE M12 hardware.
Stud (short fastener side of the engine)
102mm overall length
engaged thread length (part that screws into the block) 12mm
(usual engineering practice would require an engaged length of a minimum equal to the fasteners outside diameter, any more actually presents no more strength)
unthreaded shank 52mm
top threaded portion 38mm
Bolt (long fastener side of engine)
Under head length 105mm
threaded portion 33mm
OE ground flat both sides under nut/bolt washer 5.5mm thickness (powdered metal)
OE nut 12mm thick.
M10 bolts (victor reinz) integral washer under head (not TTY)
long 98mm under head length
threaded portion 49mm
shank is 'waisted' to 9.5mm
short 84.5mm under head length
threaded portion 50mm
shank is 'waisted' to 9.5mm
brand new unmachined cylinder head (Tipo)
thru hole length long 74.75mm
thru hole length short 60.5mm
so from all this what we really want is,
stud M10, = an engaged thread length a minimum of 10mm...
all ten threaded holes in the block have a depth of approx 33mm, all are blind holes (i.e. none present to the water jacket) and all present approx 25mm of thread (by hand) so we could have anywhere up to 20mm of engaged length here without issues of binding. Ideally we want the thread to fully engage with the block, and no additional threaded portion to be exposed above the block surface, so 20mm sounds like a safe threaded length which will be fully used... maybe 19mm would be OK as this corresponds to 3/4" given ARP is American manufactured and seem to center their measurements around imperial values.
Shank length ... short side is 52mm OEM (102mmO/A), however on the 'long' side this would only present approx 13mm for the nut and washer, simply not enough. On the 'short' side there is approx 25mm of thread exposed for the nut and washer combination above the head.
We don't want the shank portion to be too long, to allow for future head skims and thinner gasket variations, so if one threaded fastener is to be used in all ten positions, it should be 55mm in shank length (max) ... 51mm is 2" so probably a suitable number to settle on.
Threaded length for the nut. If we settle on 51mm (2") for the shank length, then this value calculates out to a minimum of 48.75mm (74.75mm [long side thru hole length] + 25mm [minimum thread for nut /washer and clearance]) so again 51mm (2") or at a pinch 45mm (1.75") would be the required top thread length.
This gives us a stud approx 115/121mm overall (19mm engaged thread, 51mm shank length, 51 to 45mm of top thread)
So using these,
http://www.summitracing.com/parts/arp-am4500-1lb
would be pretty spot on for overall length 4.5" (114.3mm) but I would be checking with the manufacturer to confirm the engaged and shank lengths, just to be sure...
The press in inserts I mentioned in another thread would also be a worthwhile improvement, basically a stepped washer (hardened and ground flat all aorund) which would require opening the head bolt thru hole out to 0.529" (13.43mm) (only at the top portion, but I regularly open M10 style heads out to 13mm to provide additional clearnace when used on M12 blocks) and inserting the washer which stays put if you machine the thru hole with a tight clearance. Check page 85 of their catalogue.
Washer, no chamfer 10mm .850 .120˝
(1pk)200-8590
(2pk)200-8591
(10pk)200-8592
would be the ARP washer to use for the head studs, suit M10, OD is 0.850" (21.59mm) almost the same as the stock washer, 0.120" thick (3.05mm) so 1 on the long side, and three stacked on the short side.
The washers being a little thinner than stock would make up for the additional few mm occupied by the stepped inserts.
I would then use High quality 17mm (10 grade) nuts, as if you use the fancy ARP 12 points, where are you going to find a retorque tool! and I can't find any hex M10 x 1.25 nuts in ARP's catalogue, only in 12 point, so I'm guessing they don't manufacture them.
so with a 115m o/a length, 19/20mm engaged thread in the block, 51mm shank length, 45mm top thread, a 2mm stepped insert washer, a 3mm hardened flat washer and a 12mm thick nut, we have 4.25mm of exposed thread (3.5 turns) which is about optimum.
On the 'short' side with 3 x 3mm washers, and everything else the same, we have 12.5mm of exposed threads, which wouldn't look out of place and shouldn't present any clearance issues for retorque tool fitment.
So your job now Rob, is to call ARP and get some exact measurements for these studs ... and if the engaged/shank/top thread lengths are 'within cooee' of these numbers... my order will be...
20 x AM4500-1LB head studs (or if they have them in kits of ten for a better price?)
2 x packs of ten 200-8598 insert washers
4 x packs of ten 200-8592 hardened washers
enough for two engines
SteveC