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[ion] C2 · 03-22-2021, 08:17 PM

I've been thinking about how best to keep the head sealed. I pretty much settled on using the Cometic MLS gasket and using ARP Custom Age 625+ (extremely high tensile strength) studs. My intention was to torque those things like crazy (75% of their yield strength) which as far as I know is something like 120 ft-lb or more. I figure this clamping force and preload will keep things snug.

However, I've read/seen some interesting things about tightening the head down with higher torque and causing distortion in the head and block, causing the cylinder walls, valve seats, etc. to be misshapen. I've seen pictures and videos of cylinder bore wear being incorrect even on iron blocks from people using higher torque on their head studs.

As power levels increase you need more strength in the stud, but you DO NOT need or want a similar major increase in preload, all you will do is distort things so they'll never seal.

When you go way over the OE torque numbers, it distorts the cylinder head

When ARP calls back with the CA 625+ cost and timing information, maybe we can ask them about their thoughts on torque/preload for this application. The assembly manual for the engine only specifies 40 ft-lb on the long head bolts, and 30 ft-lb on the short head bolts as factory specs (but that's for an engine making factory wimpy torque). I torqued all of them to 85 ft-lb when I switched to ARP 8740 studs, because that's what everyone said to use on j-body.org.

Maybe that's why I had so much crankcase pressure after this engine was built: the cylinder walls were distorted and had blow-by. Over time it sealed itself up. Who knows.

These guys are discussing the exact thought I was having - head and block should be machined with the torque plate installed at that extreme clamp load.
https://dsportmag.com/the-tech/head-...ve-efficiency/

Maybe distortion isn't a big deal and the clamping force is really necessary to keep things secure. I know some 1300+ whp 4 cylinders in this shop have head studs torqued to like 140 ft-lb.

I have the highest torque LD9 ever made as far as I know, so it's uncharted waters.

03-22-2021, 08:17 PM	#111
[ion] C2 636 whp Join Date: Aug 2006 Location: AZ Posts: 11,876	I've been thinking about how best to keep the head sealed. I pretty much settled on using the Cometic MLS gasket and using ARP Custom Age 625+ (extremely high tensile strength) studs. My intention was to torque those things like crazy (75% of their yield strength) which as far as I know is something like 120 ft-lb or more. I figure this clamping force and preload will keep things snug. However, I've read/seen some interesting things about tightening the head down with higher torque and causing distortion in the head and block, causing the cylinder walls, valve seats, etc. to be misshapen. I've seen pictures and videos of cylinder bore wear being incorrect even on iron blocks from people using higher torque on their head studs. As power levels increase you need more strength in the stud, but you DO NOT need or want a similar major increase in preload, all you will do is distort things so they'll never seal. When you go way over the OE torque numbers, it distorts the cylinder head When ARP calls back with the CA 625+ cost and timing information, maybe we can ask them about their thoughts on torque/preload for this application. The assembly manual for the engine only specifies 40 ft-lb on the long head bolts, and 30 ft-lb on the short head bolts as factory specs (but that's for an engine making factory wimpy torque). I torqued all of them to 85 ft-lb when I switched to ARP 8740 studs, because that's what everyone said to use on j-body.org. Maybe that's why I had so much crankcase pressure after this engine was built: the cylinder walls were distorted and had blow-by. Over time it sealed itself up. Who knows. These guys are discussing the exact thought I was having - head and block should be machined with the torque plate installed at that extreme clamp load. https://dsportmag.com/the-tech/head-...ve-efficiency/ Maybe distortion isn't a big deal and the clamping force is really necessary to keep things secure. I know some 1300+ whp 4 cylinders in this shop have head studs torqued to like 140 ft-lb. I have the highest torque LD9 ever made as far as I know, so it's uncharted waters.