[s-cars] Re: Valve Job Anyone?

[Kirby Smith]

Since I'm home with a cold and temporarily awake, but too dumb to know
better, I'll throw my 1787 USA half-cent into the fray.  

I find it unlikely that an Audi supervisor would approve use of a very
expensive (to Audi) steel type for the head studs, thereby cutting into
Audi's profit.  I'd bet that Audi would find another way, such as using
more studs.  Thus, the Audi stud steel could easily be of a lower
tensile strength than ARP studs.  However, lower doesn't automatically
mean inappropriate.  There may be more than enough strength.  

Why not get some steel of the appropriate thickness, drill the proper
clearance hole, torque up an ARP stud and measure the stretch.  Then do
it for an Audi stud.  Is there a significant difference in stretch?  
And at what torque does each start to fail having passed its strain
limit.  If the ARP studs prove to be stronger, then question is, is the
tensile strength of the Audi studs times their sectional areas greater
than the forces being applied to them?  What if it is the head that
deflects under cylinder pressure, not the studs?  Certainly the head
will try to squirm around.  The studs are clamping aluminum, I presume,
so some metal flow is possible, potentially reducing clamping force. 
These factors could mitigate the value of greater stength studs.

On the other hand, even if the Audi studs were strong enough I wouldn't
flame someone for buying ARP studs any more than I would flame someone
for buying airplane insurance, even though probability theory suggests
that they are wasting money.  

kirby


Mihnea Cotet wrote:
> 
> Heck, I'll throw my 0.02 Euros in here too then :-) and don't forget that
> right now 2 Eurocents is worth more than 2 murkin' cents :-))))
> 
> I am fully with Scott on this one. ARP studs are useful if you're having
> permanent head gasket issues, i.e. you have to swap the head gasket every
> few months, even once a year. AFAIK and IME, this has never been a problem
> for anyone running a 20vt engine, unless that person would have used the
> stock, NLA paper head gasket every time.
> 
> So, really, what's the advantage in having studs over stock stretch bolts
> in a high performance engine? If the bolts are torqued properly, they will
> never be a problem by themselves. ARP studs are more expensive (I think 3
> times more expensive but I might be wrong) than stock bolts and if you
> don't replace at least 3 head gaskets over the lifetime of your engine,
> they aren't worth the expense. So if it's a matter of having "ARP head
> studs" written in an extensive signature line describing all mods, then I
> agree, it's "better" to have ARP studs than stock stretch bolts.
> 
> Now if you're having head gasket issues on a 20vt motor, the problem is
> elsewhere and it has to be found and solved and ARP studs won't be an
> advantage at all over the stock bolts.
> 
> Mihnea, bolting heads up in Belgium and not knowing nuttin' 'bout dynos and
> studs, C.
> 
> <succeeding flack snipped but available from the archives>