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ARP headstuds VS OEM headbolts - 4AGE oil flow/clearance.


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#1
assassin10000

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Here is some info regarding using headstuds vs. stock head bolts and the issue oil flow & volume to the cyl head on the 16v 4A-GE engine.


After reading a post a couple months ago it stuck a thought in the back of my head, "Am I really going to hurt anything by using ARP headstuds instead of OEM headbolts due to the differences in diameter?"

I did run them for 3+ years on my old motor with no upper end issues. And many others have as well with no problems. But that's not to say there couldn't have been one we've all been lucky enough to avoid.


Since right now I've got my cylinder head and block back fresh & clean from the machine shop (basic rebuild, no perf parts - no spare $) I decided to take a look into this by measuring & calculating the area's where oil is flowing through to get the cylinder head, starting with where it comes out of the block and goes up around the head bolt/stud and into the cyl head oil galley/passage.


The measurements (starting with the important one - since it defines the smallest area oil flows through & dictates what the min. allowable area/volume will be):
1.85mm - head passage/galley I.D.
6.15mm - block passage/galley I.D.
8.5mm - OEM head bolt O.D.
9.95mm - ARP head stud O.D.
11.05mm - Cyl head opening (for bolt/stud) O.D.

Calculated area (approx.):
2.69mm - head passage/galley
29.7mm - block passage/galley
56.75mm - OEM head bolt
77.76mm - ARP head stud
95.90mm - Cyl head opening (for bolt/stud)

Now, don't forget since were working with oil under constant pressure flow dynamics aren't as huge of a deal. But having a 'minimum' of area for oil to flow through; equal to OR matching the smallest point it flows through in an OEM setup is the goal (IMO). In other words, don't choke off the oil supply volume/area. It's your engine's life blood. In this case that point is the passage/galley in the cylinder head that is supplied by the oil coming up around the head bolt/stud.


Since the only thing being changed here is the difference between the area (and volume) between the OEM bolt & ARP stud. Let's compare by subtracting the area the bolt/stud takes up from the available area in the cylinder head bore and you get the area oil can flow through:

39.15mm - OEM head bolt
18.14mm - ARP head stud

No worries yet, still plenty more than the minimum area necessary (the head passage/galley - see above) But, you also have to take into consideration the clearance available between the cyl head opening/galley & head bolt/stud as that can also bottleneck oil flow. I think this is where Dan/Oldeskewltoy was really concerned, and what has been stuck in the back of my mind.

Clearance's (not area's - that'll be important just a bit further down):
1.275mm - OEM head bolt
_0.55mm - ARP head stud

But don't forget, the oil is under pressure and will come in/up/around/through from ALL sides. So the real calculation that is important is the area around the passage/galley opening to the bolt/stud.

Area of clearance for oil to flow through:
7.41mm - OEM head bolt
3.19mm - ARP head stud

Calculated by taking the clearance between cyl head opening & bolt/stud x circumference of the cyl head oil galley. (The area that oil can flow into the galley is basically cylindrical for these purposes, since it's under pressure... I think.)


In the end it all boils down to:
3.19mm > 2.69mm

So you are OK if using ARP headstuds. (But it sure was close in my mind and I was worried until I did the #'s)

Andrew

#2
assassin10000

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FYI: there are other people who have had issues, and are still cropping up. So check your bore & fitment. Slightly warped heads, off-center holes, bore size variance can all cause a problem on YOUR motor.

ARP studs are a 'race' product and checking things before assembly is part of your job building a motor... unless you have a shop do it that will warranty it.

Andrew

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