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Subject ARP 8740 vs ARP2000 vs stock... the truth vs the hype
Posted by LitlElvis on September 12, 2017 at 8:44 PM
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In Reply To Who's using the ARP Chromoly vs ARP 2000? posted by Zbullet on September 10, 2017 at 10:59 PM
Message I tensile tested some stock head bolts in 2010 and posted the results here.

Comparing my measured tensile strengths to ARP's published data for their different materials, both yield (YTS) and ultimate (UTS), gives us:

ARP 8740.....180.........190
ARP 2000.....200.........220

As we can see from the tensile testing and from ARP's published data, the ARP 8740 material is stronger than the OE head bolt material.

Fact #1, it doesn't matter how much stronger the fastener is over stock if you don't preload it to take advantage of its increased strength. This means the higher the YTS, the higher the torque can be to increase the preload on the fastened joint... but do you need this additional strength?... see fact #2.

Fact #2, the cylinder pressure required to make around 800WHP with the VG30 isn't high enough to overcome the preload of a properly torqued stock head bolt... at this power level, it's detonation that causes cylinder pressure spikes high enough to do this. To no fault of the fastener, the detonation is caused by over-zealous tuning for the fuel being run at the time.

I personally prefer head studs over stock bolts because a stud moves the friction point during torquing from the block's relatively fragile cast iron threads to the stud and nut, both of which can easily be replaced. I use the stock head bolt washers because they are not only the correct diameter but they are also thicker than the ARP washers which massively reduces the amount the washer will flex when exposed to a load an ensures the head gasket receives as much fastener preload as possible.

In my opinion, if you aren't planning to make more than 900WHP, stock head bolts or ARP 8740 studs are the best economical choice. More than 900WHP? Move on to ARP2000, L19, or CA625+ to handle the increased cylinder pressure that comes with more power and torque them appropriately to take advantage of their increased tensile properties and keep the head gaskets happy.

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