But, while we're on the subject of cylinder head flex, hopefully you don't mind discussing it a bit. Is the flex issue typically heat related or pressure related? How much flex are we talking about? Have you guys ever implemented anything to combat it? Do you agree that a larger diameter stud could help?

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Pressure, usually from detonation. We don't do anything out of the ordinary to combat it. Proper machining, assembly, parts combination and tuning take care of it. I disagree that larger studs will help. . Like I said before, you can use the biggest, baddest fastener you can find but it doesn't stop the head from flexing/lifting between the fastener points. The only thing that will help is to put more fasteners around each cylinder but there's no room for that.

There are situations where you'll never get it to seal up- like race setups with big boost. We'll run a filled block and a welded cylinder head deck in that case.

Cdc1221 said:

Just to add a little flavor to this thread from the turbo diesel side, while i was working as a ford dealer tech we had several f-250s come in with blown hg's and if i remember correctly, the attributing factor to this was head bolt material being too weak and stretching too much so we were required by ford to replace them with better quality bolts and retorque them to factory specs

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That was a different scenario. The problem there was defective bolts supplied to Ford at the factory. Purchasing and installing ARP studs on affected vehicles was a cheaper alternative to sourcing replacement bolts and issuing a recall.

JacksonAuto said:

Pressure, usually from detonation.

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Yep. If you can't keep head gaskets in with regular ARP's and a stock style headgasket, your tune needs to be adjusted. There's a guy on here that was almost in the 9's on a 35r with pumpgas and stock headbolts for christ sake.

The other thing to look at is that the HG can act like a fuse. You get a bad tune, and knock a bunch, it puts out a headgasket. You get these badass studs in and a unblowable HG, then you knock untill a rod is poking out the side...

JacksonAuto said:

I disagree that larger studs will help. . Like I said before, you can use the biggest, baddest fastener you can find but it doesn't stop the head from flexing/lifting between the fastener points. The only thing that will help is to put more fasteners around each cylinder but there's no room for that.

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Here's my reasoning behind why I think 1/2" could help with flex issues.

Consider two cylinder heads, one with 11mm studs and the other with 50mm studs. Hypothetically, of course. The 50mm studs are stronger and larger in diameter, which would distribute the clamping force to a wider area. Theoretically, this would help reduce unwanted flex between cylinders. Futhermore, the distance between studs is reduced as well. Both, to some degree, help accomplish the same goal as running more studs per cylinder.

1/2" studs are 15.5% larger in diameter than 11mm studs. Although not near the difference of a 50mm stud, but the same improved load distribution would apply to a 1/2" diameter stud just the same.

99gst_racer said:

... 1/2" studs are 15.5% larger in diameter than 11mm studs. Although not near the difference of a 50mm stud, but the same improved load distribution would apply to a 1/2" diameter stud just the same.

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Totally understand and support your educated theory. Basic level of understanding physics will support this case. Not sure why Jackson is not on board ...

So what ever came of this? I have looked all over about this subject but it only brings me back to this thread. Were there ever any results or conclusions about this mod? I'm in the process of getting my 6 bolt spare block machined and was contemplating doing the 1/2 inch stud mod but this thread just kinda of stops with no sure answers as this being worth it or just stick with the l19's

Check the first page of this thread.

The guys at Force Engineering have done this several times since this thread was created and have found success in it. John or Tyler would have to chime in for any more info than that.

Personally I would just stick with 12 mm L19s. They are plenty big

TSIfreek said:

Personally I would just stick with 12 mm L19s. They are plenty big

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I agree 100% for this has worked flawless for many dsmers for years and has proven to be the choice of many experienced builders including myself. If a head is lifting the 1/2 stud is a bandade to a bigger issue.

If you plan to make real power, and you have room in the budget this is an option that certainly has merit.

Specifically for the reasons Paul had highlighted.

Not only will the bigger stud diameter allow you to use a wider washer while still keeping a low profile to spread the clamping force through more of the (relatively soft) head, but greater thread surface area in the block allows s similar effect on the other end of the stud.. spreading out stress internally because you are now engaging more material directly.

Here's an ASTM paper that touches on thread contact area.
http://www.astm.org/DIGITAL_LIBRARY/JOURNALS/TESTEVAL/PAGES/JTE100806.htm

The rest is well understood and described through elastic modulii in materials engineering.

Discussion is nice and all, but not everything is subject to opinion. This is a quantifiable physical effect.

Outright dismissing things you don't understand in favor of something you're more familiar with is foolish and short-sighted.

This mod is especially relevant as these half-mile and longer events become more popular. More folks are going to learn the hard way that keeping headgaskets in past 1320' requires thinking outside the box.

TSIfreek said:

Personally I would just stick with 12 mm L19s. They are plenty big

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Not all 4G63's have 12mm studs. The whole premise here revolved around going from 11mm to 1/2".

Paul going from 11 to 12mm is a big step by itself. Personally I dont see anyone needing anything over 12mm tool steel studs in a 4g63 block.

They're not using tool steel head studs. The 1/2" studs they are using are the standard arp 8740 bolts.

TSIfreek said:

Paul going from 11 to 12mm is a big step by itself. Personally I dont see anyone needing anything over 12mm tool steel studs in a 4g63 block.

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Our reasoning was that if you're going to mess with drilling and tapping a 7-bolt block for a larger stud, why stop at 12mm when the 1/2" 8740 studs cost half as much as H11/L19 studs and potentially offer a wider and more uniform clamp?

Well I think I'm going to give this mod a shot and see what happens, I talked to my machinist and he thinks is a good idea as well after I showed him this thread. We went to force engineering website and saw that this mod is offered in their stage 3 build good for 900hp so obviously they are having success with it. Now the question is where and what part number do I need to buy these?

LordDigi said:

Not sure why Jackson is not on board ...

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Because it's the block and head distorting, not the studs. Additionally, using larger diameter studs moves the clamping forces even closer to the cylinder walls which will exaggerate the effects.

JacksonAuto said:

Because it's the block and head distorting, not the studs. Additionally, using larger diameter studs moves the clamping forces even closer to the cylinder walls which will exaggerate the effects.

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Wow! Good point!

JacksonAuto said:

Because it's the block and head distorting, not the studs. Additionally, using larger diameter studs moves the clamping forces even closer to the cylinder walls which will exaggerate the effects.

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I've seen personally on a strain gauge (backed up with a noise analysis) on a similar application where engaging more material with the same load had decreased the strain. Per Hooke's law strain is proportional to stress.

Because this experiment decreased the local "stress concentration." This is a lattice structure we are dealing with. I maintain my hypothesis that spreading the clamp should provide a net benefit.

Hooke's law applies to the stretching and deformation of an elastic body which in this case would be the stud. It does not apply to how the forces affect the cylinder deformation. Your hypothesis may apply to studs of differing material or tensile strength but is not relevant to my statement regarding deformation due to larger diameter or proximity to the cylinder walls. My statement is not a theory or hypothesis. I have seen firsthand how a larger stud changes how a cylinder deforms by using a torque plate and a calibrated and certified dial bore gage. For the sake of this conversation I stand behind my comments that a larger stud will not combat cylinder head lift or deformation.

JacksonAuto said:

Hooke's law applies to the stretching and deformation of an elastic body which in this case would be the stud. It does not apply to how the forces affect the cylinder deformation. Your hypothesis may apply to studs of differing material or tensile strength but is not relevant to my statement regarding deformation due to larger diameter or proximity to the cylinder walls. My statement is not a theory or hypothesis. I have seen firsthand how a larger stud changes how a cylinder deforms by using a torque plate and a calibrated and certified dial bore gage. For the sake of this conversation I stand behind my comments that a larger stud will not combat cylinder head lift or deformation.

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I need to come hang out with you guys for just one week

The fact that you can measure the deformation in both block and stud deconstructed your own rebuttal regarding elasticity. It's plasticity that Hooke's law is not used to describe.

The cast iron IS subject to this description however.

So, we'll have to agree to disagree there.

Call it whatever you want, but a larger stud isn't going to fix a problem related to the cylinder head lifting from excessive cylinder pressure.

I've seen more than a few cylinder heads "crush" under the washer when they were either over-torqued or a higher strength stud was used. In this case a larger stud and washer would help but when it comes to preventing cylinder head lift you're off the mark.

Well it looks like I might just end up sticking with the 6 bolt L19's after all for this build. But I do have a revised 7 bolt as a spare that I would like to try this mod on, if anyone can give me a part number on a set of these or point me in the right direction of where to get them it would be greatly appreciated!

I did this on a customers drag 2g and it has worked perfect for 2 years of low 9 high 8 sec passes.