advantages and disadvantages to running ARP Head studs

[Tim]

It looks like I will be pulling my heads again and making some more changes. So, what are the advantages and disadvantages to running ARP Head studs versus using the head bolts?
What type of metal are they made from as of course we would not want corrosion from dissimilar metals?
I will be staying normally aspirated with my Stryker setup.
Thanks
Tim

 

[Vic]

I think when you run head studs, (rather than bolts) more of the applied tightening torque becomes clamping force, than it does with head bolts. Someone told me that a long time ago, but what do I know... Its not like I did my due dilligence with a strain gauge, in a controlled laboratory test.

Moly grease works better on the threads at high torque values, than regular grease. Less wasted torque overcoming the friction of the threads. When you use Moly grease, ARP reccomends reducing the torque slightly.

But the biggest reason to use them, is in case someone asks you if you used ARP head studs, so you can answer "Yes, whaddaya think, I'm a dummy?" Being caught w/o ARP head studs, is like being caught whacking it. Not that I would know, a friend told me.

 

['Trust']

ARP studs (or any stud) provide much better clamping force than factory bolts. It is hard to explain so here is some verbatim from an article:

"During engine assembly or maintenance, a bolt must be installed by torqueing it into place. Due to the head bolt’s design, it has to be rotated into its slot in order to engage the threads and secure it into place. This process creates both twisting force and a vertical clamping force, which means that when the cylinders within the engine’s combustion chamber begin accumulating load, the bolt will both stretch and twist. Because the bolt has to react to two different forces simultaneously, its capacity to secure the head is slightly reduced and it forms a less reliable seal in high-powered engines.

By contrast, a head stud can be tightened into place without any direct clamping force applied through the tightening. A stud can be threaded into a slot up to “finger tightness,” or the degree to which it would be tightened by hand. Afterward, the cylinder head is installed and a nut is torqued into place against the stud. The nut torque provides the clamping force, rather than the torque of the fastener itself, and the rotational force is avoided entirely. Because the stud is torqued from a relaxed state, the pressure from the nut will make it stretch only along the vertical axis without a concurrent twisting load. The result is a more evenly distributed and accurate torque load compared to that of the head bolt. This ultimately translates into higher reliability and a lower chance of head gasket failure."

ARP's are 8740 steel but I've never heard issues of them being mated up with aluminum, I've had them on 2 cars, and the latest making 20psi with no sign of lifting the heads.

 

[apun]

Do head studs need to be retorqued periodically?

 

['Trust']

No they do not, they are not stretch to yield. If you have a lot of cylinder pressure (15psi of boost +, assuming stock stroke) you may want to check the torque every 6 months or so.

 

[Tim]

Are the gaskets and then the heads put on, studs torqued into place then the nuts torqued up?
Can the studs and nut’s be reused multiple times or should they be replaced after a couple of installations?
Thanks
Tim

 

['Trust']

You can reuse headstuds, since they aren't stretch to yield they don't get out of shape when you torque them. I always put headstuds on first, then fit the gasket around them (insures proper gasket fitment, and you won't be hurting the gasket by twisting studs rubbing up against them). Studs torqued first, lay the gasket, put the head on, torque the head on.

 

[Tim]

How tight do you torque the studs to? Then the nuts on top are torque to the 90’ pds in 2 steps? And I assume I can re use the nuts when I disassemble the top end again? So far I don’t see any negatives here.
Thanks
Tim

 

[Chuck 98 RT/10]

I don't think there is any need to torque the studs into the block. It doesn't make sense to do so, but if there's a good reason somebody explain please.

 

[Jack B]

Some more detail:

1. The stock Gen 2/3 head bolts are not taken to the plastic region of yield. The Gen 1's had that type of bolt.

2. Typically all head bolts are taken into the elastic range, this is part of what maintains the torque.This applies to the head studs also.

3. The hardest part (time) of installing the studs is cleaning the threads in the block. You do not use a stand tap. An undersized tap made for cleaning the threads should be used.

4. You do not want to bottom the studs, take it down to the bottom and bring it up a little. I used blue thread locker.

5 The problem with head bolts, especially deep bolts like the viper is that a large part of actual torque goes into over coming the frictional forces that run the full length of the threads. Less then 50% of the observed torque is turned into clamping force.

 

[Camfab]

Here's the other side of the coin. Years ago on a small block 400 block, which by the way has very little meat between the cylinders, I ended up cracking the block at each and every stud between the cylinders. This probably won't happen on a Viper, but it shows how much additional force is applied to the block when you use the same factory specs. In an Ideal world if your changing to studs, you should be boring and honing the block with those studs in place with the addition of torque plates. If you simply add studs to your old short block you will distort the cylinders and typically loose ring seal.