OEM Head bolt/gasket strength discussion

[STeeL25T]

I want to discuss the strength of our OEM head bolts and gaskets and how they compare to their expensive aftermarket replacements and decide if they are nessesary upgrades.

I think that paying 320ish dollars is a lot of money for a pieced together set of bolts you have to modify to work. I was trying to look up some of the benefits on NASIOC, one place claims to have done testing showing the ARP bolts to be no stronger than OEM (I'm assuming they tested this on STi bolts, not sure if the grade of hardware is any stronger than ours) however ARP wins out when they get used in high heat road racing but that isn't something I see myself doing. Other threads there claim reusing OEM headbolts is no problem with the FSM Subaru retorquing method and even the offical Subaru techs do not change the bolts, so the fact that ARP is reusable doesn't stand up either.

I havn't found out the grade of hardware the OEM bolts are, but if they are grade 8 then they're supposed to be good for up to 150,000 psi... right? If thats what we got then is it worth another 200+ bucks for 170,000 psi strength?

Next up is the head gaskets, I don't know about these. A lot of people had problems with Cometic from what I read, I know the thickness has changed on the new rev of these they sell for us so maybe thats been corrected? The thread I read suggested that unless the block is machine perfectly flat then an OEM gasket will probably perform better.

You guys have the experience with these motors, what do you think?

[Sov13t]

I am sure others will chime in on this with more credibility... especially YT...

Based on my research the weak point in the bolt is the fact that it has a hat, that hat when torqued is twisted and thus the bolt is under two forces, one that is twisting the cap to stay in place (the torque) the other is the vertical clamping force... well the stud on the other hand only has that "vertical" component... it is only doing what it is supposed to do and that is clamp down the heads to the shortblock. The bolt is prone to grow weaker due to this constant torque on the hat and thus stretch or even snap.

As far as I know the ARP studs are rated to 190k psi and are of way better material than our 17 year old head bolts are... (you could go on arp site to look for the exact materials and what not).

As far as cometic's... we all know that the stock headgaskets are weak... maybe due to their age.... now noone has had cometic's long enough to say anything about their durability or have had an engine that would push their limits performance wise... Dan's engine and that EFI EG33 might be the best examples thus far.

The school of thought has been, if you are building an engine for F/I you better get some beefier studs and gaskets in... The cometics are impressive... if I am not mistaken they have 5 layers of MLS and are quite a bit thicker than stock ones.

Price is a PITA though... I agree :(

my 2 cents

[STeeL25T]

This is all stemming from me calling ARP and them having no idea at all how to help me and said I would have to call them back with exact measurements and quantities of the bolts I needed, which I didn't know. So finding that info was a pain here, but before I found it I found this:

http://www.subaru-svx.net/forum/showthread.php?t=32054&highlight=headbolts

So I tried contacting headbolts.com to ask them what brand and material their bolts are made of to verify what he said, but I mistakenly said head "studs" instead of bolts and that led them to correctly assume I was an idiot and not answer my question correctly and they haven't returned my reply for 3 days, so I just went ahead and bought a set today. When I get them I'll see if they are OEM Subaru bolts or hopefully something stronger. If they're no good I can return them within 45 days for any reason as long as I don't use them so I figured what do I have to lose?

I have at worst (hopefully) new OEM bolts coming and I already have new OEM head gaskets, so lets not accept age as a factor here.

[Sov13t]

Well, you will be running into the unknown... as far as I understand you are trying to run F/I on your build. If that is the case... the bolts will be seeing spiked pressures, don't think anyone has done it before. Hope it works out for you.

Our engine builds are expensive and studs in comparison to other components are actually cheap. And you should consider the fact that they are running extinct... as all of the parts are dwindling in their supply. That includes the Cometics aswell :( (my opinion)

When I was purchasing my studs they were actually out of the shorter ones, and didn't want to do another run unless I had a commitment of a 1k units... I guess with OT and YT contacting them as LEGAL businesses changed their mind.

-Sov

[SVXRide]

Free the SVX ARP Head Stud 7!






(or whatever the exact number is..:rolleyes:)
-Bill

[STeeL25T]

I'm just thinking now that a lot of people buy things for cars without knowing exactly why, these guys have this so I have to have this to do what they do kind of thing. I'm living proof of this haha. I'm saying that surely there's another company out there some where in the world that might make a bolt about as good as ARP, so I'm trying to find some other options. I also have all my old stock head bolts to mess with, so I'd be happy to test them to see exactly when they break... if I knew of a place to take them to that could find that out haha.

[SVXRide]

FYI
I've tried headbolts.com a couple of times with no luck. I honestly think our only real options are OEM and ARP.
-Bill

[STeeL25T]

No luck like how? As in they couldn't get you the bolts?

[SVXRide]

Went through the ordering process on line a couple of times and at the end when you actually complete the order it comes up that they're out of stock. I honestly believe they don't carry them in the first place. It would be great if you could prove otherwise! :cool:
-Bill

[STeeL25T]

I hope I can haha, I paid for them and they sent me an e-mailing saying they are beginning the transaction process, but I haven't heard anything since.

[STeeL25T]

I got my head bolts in the mail last night from headbolts.com, pretty quick I must say. Now though the real fun begins, now how do we find out the strength of these bolts?

The bolts I recieved are not from the same manufacturer claimed in the post I linked to, these head bolts are made by Corteco, part number 27138. I'm still at work and have not opened them, but when I get home tonight I will check them side by side with my OEM head bolts to see if the sizes are right and check for any markings on the bolts. A quick search of their website didn't find me anything on their strengh rating or what material they are made of, maybe someone else can find something?

[STeeL25T]

Opened it up and pulled a bolt out, the bolt has 5 stars marked on the top and below it the number "11.9".

According to the thread I linked to, he claimed the bolts he got were 11.9k bolts that transalted to 169,xxxx tensile strength. Can anyone confirm thats translated right, and number two if thats what I have?

[SVXRide]

11.9 =

Ultimate Tensile strength of 1100 MPa (159,500 psi)

Yield Tensile Strength= 990 MPa (143,550 psi)

During engine assembly or maintenance, a bolt must be installed by torquing it into place. Due to the head bolt’s design, it has to be rotated into its slot in order to engage the threads and secure it into place. This process creates both twisting force and a vertical clamping force, which means that when the cylinders within the engine’s combustion chamber begin accumulating load, the bolt will both stretch and twist. Because the bolt has to react to two different forces simultaneously, its capacity to secure the head is slightly reduced and it forms a less reliable seal in high-powered engines.

By contrast, a head stud can be tightened into place without any direct clamping force applied through the tightening. A stud can be threaded into a slot up to “finger tightness,” or the degree to which it would be tightened by hand. Afterward, the cylinder head is installed and a nut is torqued into place against the stud. The nut torque provides the clamping force, rather than the torque of the fastener itself, and the rotational force is avoided entirely. Because the stud is torqued from a relaxed state, the pressure from the nut will make it stretch only along the vertical axis without a concurrent twisting load. The result is a more evenly distributed and accurate torque load compared to that of the head bolt. This ultimately translates into higher reliability and a lower chance of head gasket failure.

and a little bit more....

Application:
Street/Race
ARP 154-3603 Cylinder Head Bolt Kit
Fits 351W Ford V8 with Edelbrock heads 60259, or 60379.
ARP's "High Performance" series cylinder head bolts feature a reduced wrenching hex or 12-point head and a wide area flanged head that eliminates the need for valve train removal to facilitate cylinder head retorquing. All High Performance Series bolts are rated 180,000 psi tensile strength (which is 15% stronger than Grade 8) and all sets include hardened steel parallel-ground washers.
Available with hex heads only.
ARP 154-3603
• ARP's "High Performance" bolts deliver superior strength and are rated at 180,000 psi
• Cold forged and heat treated
• Ideal for all high performance applications
• Reduced hex size for more clearance around valve train components
• Application specific
Last Updated: 2010-01-11 19:02:37

[STeeL25T]

Where'd you find that out from? Every single chart I could find said that 11.9 was not a class of metric bolts.

If the correct ARP bolts actually exist, and are not like Big Foot, I'll probably end up getting them. I just thought this was worth a try.

[SVXRide]

I'm a mechanical engineer by training...;):D

My guess is that you found 10.9 and 12.9, as they're more common. Bottom line is that with metric bolts, the number to the left of the decimal point x 100 MPa = the ultimate tensile strength, while the number to the right of the decimal point x 100 MPa = the yield tensile strength. While not exact to several decimal points, you can use 145 x the number of MPa to get psi

-Bill

[STeeL25T]

Any idea what the part numbers are for OEM head bolts?