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58mm of Bliss
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Head bolts/studs are a very discussed topic, and not just in the BMW FI world. In most cases, many people seem to go with X because its what someone else did. I started asking "why", and that lead me on quite an interesting journey in the motorsport world.

Some may remember the M54 bock and heads that I cut into slices last year. Some of that was to evaluate head stud options, and some of it was to look at matting surface stiffness. I sent measurements and pictures to quite a few motorsport companies to get their feedback on various concerns. The result kind of surprised me.

Over 80% of the "load" on a fastener is held on the first 4 threads of engagement on like materials. A good example of this would be the nut and a bolt. On an engine block, we often thread the head bolt or stud 15-20 threads deep. What's up with that? Un-like materials.

The greater the difference in tensil strength between materials, the more thread engagement is required. There comes a point however where the thread engagement holding capacity exceeds the tensil strength of the fastener outside of the block. When this happens, it won't matter how many threads are engaged on the block...the fastener will stretch without pulling out of the block under load.

Installing a bolt on an engine block applies a twisting, as well as pulling force on the block threads. To distribute this force so that the fastener and the block doesn't get damaged, BMW uses a lot of threads. If BMW used studs instead of bolts to hold down the cylinder head, you'd find a lot less thread depth in their blocks. So yes, the thread depth is over-kill when using studs on most production blocks.

So if more thread depth is unproductive, how do we increase cylinder head clamping ability?

Increasing the tensil strength of the fasteners, and/or increasing the size of the fastener.

Before that is done though, one of the simplest ways of increasing the cylinder head clamping ability is to convert from a bolt to a stud. A stud applies next to zero twisting force on engine block threads when being torqued down, which increases the amount of load you can apply to the engine block threads in one direction.

Increasing to a larger cylinder head stud, from 10mm to 11mm for example, gives a significant increase in clamping force potential. The gains come both from the strength of the larger diameter fastener, and the increased surface area of the thread matting surface in the block. Thread depth? Not really a concern.

So for those looking to hold their cylinder head down with big power: Pursue a stronger fastener material, preferably a stud, and a larger diameter fastener. Forget about increasing thread depth on the block.
 

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Head bolts/studs are a very discussed topic, and not just in the BMW FI world. In most cases, many people seem to go with X because its what someone else did. I started asking "why", and that lead me on quite an interesting journey in the motorsport world.

Some may remember the M54 bock and heads that I cut into slices last year. Some of that was to evaluate head stud options, and some of it was to look at matting surface stiffness. I sent measurements and pictures to quite a few motorsport companies to get their feedback on various concerns. The result kind of surprised me.

Over 80% of the "load" on a fastener is held on the first 4 threads of engagement on like materials. A good example of this would be the nut and a bolt. On an engine block, we often thread the head bolt or stud 15-20 threads deep. What's up with that? Un-like materials.

The greater the difference in tensil strength between materials, the more thread engagement is required. There comes a point however where the thread engagement holding capacity exceeds the tensil strength of the fastener outside of the block. When this happens, it won't matter how many threads are engaged on the block...the fastener will stretch without pulling out of the block under load.

Installing a bolt on an engine block applies a twisting, as well as pulling force on the block threads. To distribute this force so that the fastener and the block doesn't get damaged, BMW uses a lot of threads. If BMW used studs instead of bolts to hold down the cylinder head, you'd find a lot less thread depth in their blocks. So yes, the thread depth is over-kill when using studs on most production blocks.

So if more thread depth is unproductive, how do we increase cylinder head clamping ability?

Increasing the tensil strength of the fasteners, and/or increasing the size of the fastener.

Before that is done though, one of the simplest ways of increasing the cylinder head clamping ability is to convert from a bolt to a stud. A stud applies next to zero twisting force on engine block threads when being torqued down, which increases the amount of load you can apply to the engine block threads in one direction.

Increasing to a larger cylinder head stud, from 10mm to 11mm for example, gives a significant increase in clamping force potential. The gains come both from the strength of the larger diameter fastener, and the increased surface area of the thread matting surface in the block. Thread depth? Not really a concern.

So for those looking to hold their cylinder head down with big power: Pursue a stronger fastener material, preferably a stud, and a larger diameter fastener. Forget about increasing thread depth on the block.
I saw your cylinder head slicing thread and I wonder how much material there is between the water jackets and the head bolt holes to go an extra 2mm to use a 12MM stud/washer/nut combo.

We use 12mm on our SRT-4 engine now, we have A1 studs/nuts/washers.
even the 11mm, they hold 750whp on our cars and 40psi.
 

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Didn't someone use ARP studs on the M54 engine and ended up lifting the head on high boost? I remember some company used ARP and the head kept lifting, but then used OEM BMW head bolts and the head didn't lift. :dunno:
 

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Didn't someone use ARP studs on the M54 engine and ended up lifting the head on high boost? I remember some company used ARP and the head kept lifting, but then used OEM BMW head bolts and the head didn't lift. :dunno:
ARP doesn't make a stud for the M54 engine. I may be mistaken, but I think the instance you're referring to used the ARP M52/S52 stud, which has less thread engagement. What ended up happening were the threads got stripped in the block due to the fewer threads engaged by using the M52 based studs.

Again, I may be wrong about the details of the story, but I know that ARP doesn't offer an M54 specific solution.
 

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ARP doesn't make a stud for the M54 engine. I may be mistaken, but I think the instance you're referring to used the ARP M52/S52 stud, which has less thread engagement. What ended up happening were the threads got stripped in the block due to the fewer threads engaged by using the M52 based studs.

Again, I may be wrong about the details of the story, but I know that ARP doesn't offer an M54 specific solution.
Is that what happened on Benvo's car?
 

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ARP doesn't make a stud for the M54 engine. I may be mistaken, but I think the instance you're referring to used the ARP M52/S52 stud, which has less thread engagement. What ended up happening were the threads got stripped in the block due to the fewer threads engaged by using the M52 based studs.

Again, I may be wrong about the details of the story, but I know that ARP doesn't offer an M54 specific solution.
That would seem the most logical situation, wrong hardware would cause this issue.

The correct hardware on the stock block should hold enough for 35psi.

Has anyone contacted one of these Fastener companies if in fact they would manufacture a M54 specific kit?
 

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58mm of Bliss
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Discussion Starter #8
Has anyone contacted one of these Fastener companies if in fact they would manufacture a M54 specific kit?
Raceware makes a kit for the M54.

I've got a set of those on the shelf for testing, as well as a custom set of 11m studs for a new project.

You can ask for anything you want, and they'll make them...it just costs...and sometimes you have to buy a few. (My pistons are a good example of that)
 

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I wonder how much thread engagement the m5x/s50/2 arp2000 studs have when compared with stock bolts. These are the bolts that are holding my engine together, but instead threaded into steel inserts. I know that in racing use of the m54, there was a problem, probably caused by overheating in which the stock bolts would strip out of the block. The solution in my block was a direct recreation of a head-clamping solution made for some class in which the m54b25 was popular, I think Koni.
 

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58mm of Bliss
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The solution in my block was a direct recreation of a head-clamping solution made for some class in which the m54b25 was popular, I think Koni.
Koni cars ran/run M54B30s, it was World Challenge that the M54B25s ran in. There were 3 companies that supplied these engines to that series in decent #s: JBR, Sunbelt, Rebello. The M54B25 went through a bit of oil system development for all the builders until they figured out the baffles. The N52B25....that engine was a nightmare! Head studs made rebuilding the engines easier...it wasn't clamping force that was the sole reason for using them. (More rebuilds before the block threads wore out)

As an odd side note: I know of one very well known drag racer that was using a sprayed liner on his billet aluminum blocks. Rebuilds would involve acid dipping the block to prepare for the liner to be re-sprayed. After a couple of "rebuilds" he started noticing free-play when installing the head studs. The acid dipping was stripping material away from the block....including the threaded areas.
 

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At what point is it recommended to replace the studs? I have a ESS SC running 7 psi; aren't the oem bolts adequate?
 

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this may be a moron question, but if you increase the diameter of you bolts how do you put them into the stock holes? wouldnt they have to be drilled and an rethreaded?
 

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Didn't someone use ARP studs on the M54 engine and ended up lifting the head on high boost? I remember some company used ARP and the head kept lifting, but then used OEM BMW head bolts and the head didn't lift. :dunno:
It was ESS: "During TS3 R&D we have only been able to make stock headbolts (10mm) and E46 M3 headbolts (11mm) work reliably over time. ARP bolts constantly caused the head to lift and head gasket to leak as they are solid bolts which does not seem to work well in the full aluminium M54 engine due to their non-stretch design. Therefore we strongly recommend against using anything else than stock BMW head bolts with the TS3."

http://forum.e46fanatics.com/showthread.php?p=7277929&highlight=arp#post7277929
 

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58mm of Bliss
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Discussion Starter #15
It was ESS: "During TS3 R&D we have only been able to make stock headbolts (10mm) and E46 M3 headbolts (11mm) work reliably over time. ARP bolts constantly caused the head to lift and head gasket to leak as they are solid bolts which does not seem to work well in the full aluminium M54 engine due to their non-stretch design. Therefore we strongly recommend against using anything else than stock BMW head bolts with the TS3."

http://forum.e46fanatics.com/showthread.php?p=7277929&highlight=arp#post7277929
Amusing.

The person you quoted above has a TS3 on his car.
 

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Amusing.

The person you quoted above has a TS3 on his car.
I remember AJ telling me when I asked him about why do they use the OEM BMW head bolt. I just remember it being posted somewhere (too lazy too look it up), but not by who. Didn't want to put my foot in my mouth. :p
 

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Koni cars ran/run M54B30s, it was World Challenge that the M54B25s ran in. There were 3 companies that supplied these engines to that series in decent #s: JBR, Sunbelt, Rebello. The M54B25 went through a bit of oil system development for all the builders until they figured out the baffles. The N52B25....that engine was a nightmare! Head studs made rebuilding the engines easier...it wasn't clamping force that was the sole reason for using them. (More rebuilds before the block threads wore out)

As an odd side note: I know of one very well known drag racer that was using a sprayed liner on his billet aluminum blocks. Rebuilds would involve acid dipping the block to prepare for the liner to be re-sprayed. After a couple of "rebuilds" he started noticing free-play when installing the head studs. The acid dipping was stripping material away from the block....including the threaded areas.
must have been world challenge then. It was definitely one of those companies that did the machine work on my motor and executed the steel inserts. It was custom bolts that were used alongside the steel inserts. I chose ARPs as they had a higher tensile strength rating than the custom bolts and were cheaper.
 

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58mm of Bliss
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Discussion Starter #18
I remember AJ telling me when I asked him about why do they use the OEM BMW head bolt. I just remember it being posted somewhere (too lazy too look it up), but not by who. Didn't want to put my foot in my mouth. :p
Dude, I quote the wrong information all the time. This topic is a good example where I for some reason thought I had 11mm head studs on the shelf at the shop back in 2008...when they were actually 10mm.

FYI, the tensile strength of Raceware's material is lower than ARP2000s. Perhaps this is why I never had any problems?

must have been world challenge then. It was definitely one of those companies that did the machine work on my motor and executed the steel inserts. It was custom bolts that were used alongside the steel inserts. I chose ARPs as they had a higher tensile strength rating than the custom bolts and were cheaper.
I've always wanted to try using grade 8 bolts from a hardware store just to see.... Any volenteers with an engine?
 

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Dude, I quote the wrong information all the time. This topic is a good example where I for some reason thought I had 11mm head studs on the shelf at the shop back in 2008...when they were actually 10mm.

FYI, the tensile strength of Raceware's material is lower than ARP2000s. Perhaps this is why I never had any problems?



I've always wanted to try using grade 8 bolts from a hardware store just to see.... Any volenteers with an engine?
So does that mean the Raceware is in between OEM BMW and ARP2000?
 

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58mm of Bliss
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Discussion Starter #20
So does that mean the Raceware is in between OEM BMW and ARP2000?
From a "spec" perspective yes. However I think there are many other things that need to be looked at as well. For example:
  • Fastener thread shape
  • Fastener material coatings
  • Fastener installation instructions
Not all fasteners are the same, even though they share the same thread pitch. (Those of you with mechanic experience will understand what I'm talking about.) I have some really "good" tools to work with threads from Snap On, Walter, and a few others. Often the tap, die, or thread chaser has a slightly different shape than the fastener's.

The coatings will affect the amount of force a given torque value will exert on the threads. (Variance in friction)

You could have the same 2 fasteners, and they will give a vastly different result depending on the installation instructions.
 
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