Quote:
Originally Posted by Jonny042
Absolutely!!! Like I said, thanks for sharing the correspondence and for bringing this up.
I do share your concern about that 38 pounds!!!
One of the things I learned in my research on the topic which I found counterintuitive is that the same torque on a fine thread and coarse thread will result in a relatively similar clamp load on the fastener (in our case the head studs). Not the same, but somewhere in the range of 10-15% greater for the fine thread.
This is relevant because Henry Schmidt who's done a great job designing his Supertec head studs (with fine threads on the nut end) specifies varying torques for them depending on application:
So even though the ARP nuts are coarse threads and the Supertec are fine, the torque values would be somewhat comparable, keeping in mind the 10-15% difference.
In my application 30 ft/lbs would be recommended for the Supertec studs. To get a similar clamp load (of course that would depend on all things being equal which they rarely are, but given the lube provided with both studs they should be similar) you would need a bit more torque on a coarse nut.
So, I chose 32 ft/lbs. I wanted a slightly higher clamp than stock due to the plain sealing surface on the 3.2 Carrera cylinders in the motor I was building.
Given the new information from ARP I will use the same for the 3.4 I'm gathering parts for now. Already have the ARP studs I was really happy with them in the last build. Some things are subjective and intangible (like your testing!) but they just "felt" right going together.
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Cool thanks.
I had my motor out for a few things and installed new base gaskets and went with a solid 26 ft lbs on my ARP head studs. Factory being 23-24 ft lbs. I thought a lot about it.
Also, if you look at other aluminum motors 21,22,23 ft pounds is the number a lot. 38 was insane.
Type 4 VW around 21, a new Min Cooper S (I have one) is 22-23 or 20 then 90 degrees, earlier 911s: 21 ft lbs and so on. We also have (4) studs per piston. If you look at other torque spec like the cam boxes that number is 18.3 ft lbs. I'm being cautious. I can always tighten them if they loosen but I don't think they will.
I compared factory hardware and finish to ARP's which is very smooth and slippery and made my decision to not do 28 ft lbs. I used assembly lube and 5W/30 synthetic on nuts and washers.
I want the value that is lowest but tight when cold.
I'll follow up with how it goes.
Matt
