when are head studs needed?
05-10-2010, 04:54 PM
#16
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The necessity of head studs is a function of combustion pressure, which normally varies directly with boost pressure.
14mm studs aren't the best solution - machining the larger threads removes material & rigidity from the block and $$ from your BOMB budget.
ARP 2000s are fine for most builds, if you need zero failure go with the nickel-base 625+.
Studs (any threaded fastener) will stretch by design, and yield if their tensile strength is insufficient for the load applied.
Stretch is good, yield (permanent deformation) is bad... think of studs as very heavy-duty springs that barely move.
All studs stretch - the 625+ will stretch more (contain more combustion pressure) before they fail (yield)... length change (stretch) is measurable though minute - think of stretch as absorbed load.
Studs are naturally far less likely to pull threads - without tensile stress within the block's thread engagement length, load is shared equally among all engaged threads.
Bolts stretch when torqued to desired clamp load, so most of the shear stress in the block occurs in the 1st engaged thread, followed by 30% less on the next thread, etc. until the bottom end of the bolt is usually just along for the ride (until the upper threads strip out and the load is accordingly carried by the next lower threads).
Also, prevailing torque is much higher on a bolt fastener than a stud fastener (even with correct torque lube), due to the difference in number of rotating threads - so more accurate (and ultimately higher) clamp loads can be developed with studs.
If your MLS head gasket is sealing well, leave it in place and stud it (ARP 2000, A1, H11, 625+, etc.) to your desired power production goal; if the head is coming off anyhow, consider a 12V gasket & O-rings for the ultimate in cylinder head sealing.
14mm studs aren't the best solution - machining the larger threads removes material & rigidity from the block and $$ from your BOMB budget.
ARP 2000s are fine for most builds, if you need zero failure go with the nickel-base 625+.
Studs (any threaded fastener) will stretch by design, and yield if their tensile strength is insufficient for the load applied.
Stretch is good, yield (permanent deformation) is bad... think of studs as very heavy-duty springs that barely move.
All studs stretch - the 625+ will stretch more (contain more combustion pressure) before they fail (yield)... length change (stretch) is measurable though minute - think of stretch as absorbed load.
Studs are naturally far less likely to pull threads - without tensile stress within the block's thread engagement length, load is shared equally among all engaged threads.
Bolts stretch when torqued to desired clamp load, so most of the shear stress in the block occurs in the 1st engaged thread, followed by 30% less on the next thread, etc. until the bottom end of the bolt is usually just along for the ride (until the upper threads strip out and the load is accordingly carried by the next lower threads).
Also, prevailing torque is much higher on a bolt fastener than a stud fastener (even with correct torque lube), due to the difference in number of rotating threads - so more accurate (and ultimately higher) clamp loads can be developed with studs.
If your MLS head gasket is sealing well, leave it in place and stud it (ARP 2000, A1, H11, 625+, etc.) to your desired power production goal; if the head is coming off anyhow, consider a 12V gasket & O-rings for the ultimate in cylinder head sealing.
05-10-2010, 07:25 PM
#17
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14mm are completely unnecessary for just about everything except the highest hp 12v's, 1500hp+. 1000+ hp has been done quite a few times on just the standard ARP's and o-rings or a MLS.
05-10-2010, 07:28 PM
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ARP specs them at cold, A1 specs there's hot, so. Ask 10 different engine builder and you'll get 10 different answers. IMO as long as you do the proper torque specs on the first go around you'll be fine.
05-10-2010, 07:36 PM
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Works for me. I thought on a cold engine, that way a guy could do a valve set too before starting it up?
05-11-2010, 09:41 AM
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05-11-2010, 10:40 AM
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If you're taking it apart for injectors you might as well do the ARP 2000's while you are in there. I believe that valve springs are needed about 55psi.
05-11-2010, 07:33 PM
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05-11-2010, 07:56 PM
#25
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Hello,
Isn't a bottoming tap needed to run thru the block holes. That would be my preference. The studs should not be tightened down in the block. They should be run down and then backed off so they are loose. The stud itself should not be tightened. The nut on the head should be the only thing that is tightened.
Diesel studs are so so expensive compared to gasser engines. It is all part of the game of charging excessively for non-main line parts. I know there is added cost in making smaller runs of parts but NOT double, triple, and quadruple the cost. JMO.
Damon
Isn't a bottoming tap needed to run thru the block holes. That would be my preference. The studs should not be tightened down in the block. They should be run down and then backed off so they are loose. The stud itself should not be tightened. The nut on the head should be the only thing that is tightened.
Diesel studs are so so expensive compared to gasser engines. It is all part of the game of charging excessively for non-main line parts. I know there is added cost in making smaller runs of parts but NOT double, triple, and quadruple the cost. JMO.
Damon
05-11-2010, 08:56 PM
#28
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Diesel studs are $$$ due to less demand... if you want to build HP on the cheap do a SBC.
Studding a CR isn't easy for the average DIY'er - rocker cover base needs machining to clear rear stud, exhaust valve lash should be checked after reinstallation, solenoid wires have to be removed, gotta be careful on solenoid nut torque and make sure exhaust pushrods stay in tappet cups, etc.
Following stud manufacturer's instructions is also important.
Bottom tapping the block isn't worth the time if the head is in place.
You can expect 270*- 990* of extra thread engagement... at best a 5% gain in pullout threshold (which is basically never reached anyhow).
Studding a CR isn't easy for the average DIY'er - rocker cover base needs machining to clear rear stud, exhaust valve lash should be checked after reinstallation, solenoid wires have to be removed, gotta be careful on solenoid nut torque and make sure exhaust pushrods stay in tappet cups, etc.
Following stud manufacturer's instructions is also important.
Bottom tapping the block isn't worth the time if the head is in place.
You can expect 270*- 990* of extra thread engagement... at best a 5% gain in pullout threshold (which is basically never reached anyhow).
05-11-2010, 10:46 PM
#29
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Who does not want to make HP cheap? I surly don't want to overspend. We also have to spend wisely. I hate SBC through. Only do Mopar unless a friend need a hand.
The part about less demand is mostly junk. I get to see the inner workings of the cost on Cat, SeaRay, Mopar, Chevy, Building components, Honda, etc etc. when I do fire investigations. It is CLEAR that the cost of an item is mostly based on the perception of its worth to the upper management. This has a much larger affect on the final price of an object. There is no doubt that the major manufacturers have an increased cost due to less demand. But make no mistake that the perception of a part worth has a greater affect on the parts final price. In our automated world of cnc and robotic equipment there is little cost involved in making the minor changes in a part to fit one brand over another.
Damon
05-11-2010, 11:50 PM
#30
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Without minimizing any of the marketing fantasies upper management is subjected to, 3 decades of experience in manufacturing has made it clear to me that cost accounting is the major determinant in product pricing - software excluded of course (a little inside Dilbert humor there! 
) - or a company and it's products don't survive over the long term in the marketplace.
I can understand how an NFPA-ish viewpoint would create a slanted view of all hard parts based on a narrow segment of specialized safety/prevention items.
BTW - there are plenty who don't want to make HP cheap, that's why we build Mopars, Pontiacs & CTDs... it's the American way!
) - or a company and it's products don't survive over the long term in the marketplace.I can understand how an NFPA-ish viewpoint would create a slanted view of all hard parts based on a narrow segment of specialized safety/prevention items.
BTW - there are plenty who don't want to make HP cheap, that's why we build Mopars, Pontiacs & CTDs... it's the American way!