Ahh, that makes more sense. Like you said, not cheap! So the shop used conventional machining to bore through the old bolt, then the EDM die process to cut the hex into the bottom of the stud to remove it. Awesome!
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The '93-'99 blocks have head bolt holes that are ~3" deep with threads (well... time-serts in my old block) that start at ~1.325 deep.
These engines use 140mm head bolts and the head bolt bosses in the cylinder heads are ~3.010 tall. Head bolt thread engagement was ~1.175 or 2.7 bolt diameters.
I found out that several of the changes I was attributing to '04 actually happened for '00.
In '00, GM reworked the dies that form the sides of the block. They did not rework the valley die, the end dies or the crankcase die.
The side dies have the upper crank sensor boss, the cooling jacket drain bosses, most of the accessory mounting bosses, etc.
The side dies also define the casting features which receive the head bolt threads. Since GM updated these dies for '00, they lengthened the casting features that receive the head bolt threads. The lower/outer rows of head bolt holes in the '00-'03 blocks are ~3.800 deep overall with a starting depth of ~2.025 for the threads.
Since GM was not changing the valley die for the '00 update, they did not extend the casting features for the upper/inner rows of head bolts. However, since they were completely changing the cylinder head castings, they made the upper/inner head bolt bosses in the cylinder heads taller, up to ~3.660. The '00-'03 upper/inner head bolt threads are slightly deeper at ~1.380 starting depth.
Those changes to the block and heads let them increase the bolt length from 140mm to 156mm, though they kept the 11x1.5 thread.
For '04, GM switched to the 11x2.0 thread and further increased bolt length to 161mm. The upper/inner bolt holes couldn't go any deeper, but the threads actually go shallower at 1.150 starting depth. The lower/outer bolt holes got slightly shallower at ~3.600 with threads starting at ~1.800. Thread engagement went up to ~1.525.
LS's use multiple head bolt lengths. All are 11x2.0. <'04 engines use three different lengths, one of which is 155mm. The '05+ LS engines changed the design so that the longest bolt is 100mm.
Soo.... Where does that leave me?
I will be using Cometic MLS gaskets, so the stock torque sequence is out the window.
At Alan Johnson's suggestion, I used 70 ftlbs on my previous engine and had no problems.
I will install thread inserts no matter what.
Because I'm using '<99 cylinder heads, EITHER I'm limited to the 140mm early bolts or my current ARP 204-4204 studs in the upper/inner rows OR I need to machine spacers to use 11x2.0x161mm bolts with the shorter <'99 upper/inner head bolt bosses.
I need to measure out the 'serted and virgin hole diameters to see if the material is in the block to install the 11x1.5 inserts at the <'99 depth in the lower/outer bolt holes. That would let me run my current studs all around again.
I can install the 11x2.0 inserts all around at the '04+ block depths, and machine spacers to use the 11x2.0x161mm bolts in the upper/inner locations as noted above. I still need to figure out torque based on preload and buy a new set of head bolts (not expensive) but I would not be able to reuse my current studs
I can install the 11x2.0 inserts at the '04+ depth in the lower/outer locations. AND install the 11x1.5 inserts at the <'99 depth in the upper/inner locations. That would let me use 11x1.5x140mm bolts in the upper/inner locations and 11x2.0x161mm Northstar bolts in the lower/outer locations. I'd have to do some math to figure out the torque to get the clamp load right, using 70ftlbs on the 7/16-20 thread at the top ends of the ARP studs as the benchmark. I'll end up with different torques for each row.
If I "split the pitch" as described above I could also use ARP's 11x2.0 LS long studs--which *probably* have 7/16-20 upper threads--in the lower/outer locations... that at least means I use the same torque on both rows.
I need to call ARP about the upper thread and snagging 10 of those long studs, since I need to call them about ordering eight 11x1.5x0.880" LS flywheel bolts anyway.