they were at least when I did them on my buddies 6.0 a few months back but their new instructions call for 80 so idk what gives lol

 

Good information here so thank you. As noted the cost (got mine for $70 shipped) of the pro comp is relevant for a jy budget build, at least for me. Additionally it is almost unanimous in the pro comp thread in FI that you should torque 70-75 lbs max.

For the cost and relatively low boost (<22 psi) the pro comp studs made more sense to me on a $500 block build. ARP is far superior for sure but I have heard of some snapping as well whether it be installer error or other.

 

I'm all for turbos, so the ARP stuff is clearly the best choice

 

Very interesting data. The ARP's "only" provide a 17% increase over stock bolts. Lots of other good reasons for ARP studs, though. This time around I used stock replacement bolts, since the engine is pretty mild.

Pro-Comp stuff is cheap off shore copies of real American products. There's no place for any of that cr ap in my garage. You get what you pay for (if you're lucky).

 

yeah, but look at what some people are getting away with on the pro comps. Sure it may not look like a substantial strength increase with the ARP when were talking in 6 digit numbers, but im sure those are hard fought numbers to achieve, and not only achieve once, but constantly deliver time and time again through strict quality control that the ebay studs may not have. ask any fabricator about bad batches of steel, or any parts distributor about parts being bad or out of spec out of the box. All about insurance for some people.

 

Very cool, thanks for sharing. Did the lab provide the stress/strain curves? If you could get those and post them it would be very interesting.

 

I am not asking the OP to spend anymore money BUT you have to wonder about the ProComp consistency, none of us knows if that was an average example or if it was weaker or stronger. The ARP and GM I trust to be consistent, ARP because what they do is high end fasteners and GM because millions of them are in service and reliable.

 

That would be cool. From those curves you can determine the yield strength.

 

so what are the yield points for each material? It is much more complicated than stretching the bolts with an instrument and spit out the results. We need to take into consideration young's modulus, elastic and plastic points to see the actual deformation before failure. What this shows me is that the procomps are made from a less ductile material i.e. "brittle" and thus doesn't experience much plastic deformation before failure, much like carbon fiber and other materials with little plastic deformation travel. Head lift will occur much earlier than the posted results due to material travel/stretch, the results only show failure which by that point the head has already lifted due to the material's plastic deformation stage before rupture. But until the plastic points are shown for each material, we can't really jump to any conclusions as that will be the point where the stud or bolt will be permanently deformed and will not return to its normal state (what is referred to as elasticity). Another factor to consider is QC and acceptable margin of error/std deviation of material strength, uniformity in density of the material, and material purity. Don't be quick to put all your faith in ARP as they have fucked me and thousands more in the import world. Thousands of heads have lifted on mild supra builds, 300zx builds, and even on evo's. The cause was arp's stud and nut design that dug into the cylinder head under high cylinder pressures which resulted in head lift. It is also good to note that the studs never ruptured, as by the time the head lifts, the material has stretched just enough that the clamping force is minimized due to head travel, i.e. the stud will not rupture, but what good is it if the head has already lifted?

 

As you may or may not know, a higher tensile strength will typically correlate with a higher yield strength. With a higher yield strength, the fastener can be stretched to a higher clamp load than a material with a lower yield strength.

It's a pretty safe bet that based off the data, the ARP material (probably the 8740) will have a much higher yield strength, and therefore potentially a higher clamp load than the eBay studs.

It's also a pretty safe bet that since the GM bolt is torqued to its yield point while the eBay stud is not, the GM bolt actually provides a higher clamp load than the eBay stud as well.

 

in all of this where would the arp head bolts sit as they are affordable and reusable. I plan i buying the bolts because they are relatively inexpensive and reusable and there for could be use in another project if catastrophic failure occurs

 

Same. This is really a test of the properties of the material, not necessarily the design (ie bolt vs stud).

 

Clamp load is a function of torque, not the material of the stud.

 

this is true, however if the material yields then the clamp load will be diminished although some of that will be reflected in the torqueing of the bolt but not all. In this case I would expect the arp to have a higher yield strength and thus be able to generate more clamping force before the material yields and ceases "clamping"

 

No, the torque really has nothing to do with it. Clamp load can be approximated using Hook's Law. The stiffness of the material times the distance stretched will result in your clamp load.

Torque has to overcome the force required to stretch the fastener and the friction from turning the bolt/nut, so it's not really a good indication of clamp load.

 

#...rod bolt stretch guages

 

From: link


The mathematical relationship between torque applied and the resulting tension force in the bolt has been determined to be as follows:

Equation T = c D F

T = Torque required (inch pounds)
F = Bolt tension desired (Axial Load) (pounds).
D = Nominal bolt diameter. (major dia.)

c = Coefficient of friction constant

Steel and/or zinc plateds threads = .2
Cadmium threads = .16
Lubricated threads = .16 to .17

 

Like I said, it's not a good indicator because when you try to calculate clamp load with torque, you have to account for friction with some sort of coefficient which is, at best, a wild guess. Why do you think that, as your link points out, bolts that are tightened to a torque value are not recommended to exceed 80% of its yield? That's a fudge factor.

Now back to my original point, a material with a higher tensile strength will typically have a higher yield as well. If you can't exceed 80% yield, then you can only increase your clamp load with a higher yield material (ARP 2000, 625, L19, etc) or greater cross section.

 

I would be happy to request additional data if you guys tell me what you want to see. Based on the data I've seen we won't be offering this product. Sometimes Ya try stuff in hopes its a bargain. Sometimes bargains don't pan out!

 

provide elastic yield points for each fastener

and provide plastic yield points for each fastener