I'm looking at getting uprated head studs to use in the new engine I'm building. I know a few people on here are using them and just wondered if someone would mind explaining why the head is less likely to lift when using them, because I cant get my head around it.
Do they not expand as much as normal head bolts? Or are you able to have them tightened to a higher torque?
Cheers, Ben
Id talk to Darren or Ruan they know about them
Although sure one of them will come along soon and explain
It's because standaed bolts are made from weaker material and will stretch a very small amount under enough pressure. Harder grade studs/bolts won't stretch as easy
Precisely what Dan said.
Id have a speak to ARP. They do them for the mi16 iirc that you'll need to get some custom washers made up for them
From what I remember they're £200+
I know of 3 people who have issues with head studs. Me, ruan, and con. I cant see why they are needed unless you are running over 300+ ftlb of torque.
What about the site we were talking about the other night bed ? With the custom made ones.
So it is just that they don't expand as much. Last time I asked the answer wasn't so decisive so I wasn't sure.
I know I will probably not have issues with a lifting head, but these would in theory make it a more reliable engine and would also mean it would be ready for bigger power in the future.
And Jake I will probably try and get a quote from them soon.
(11-09-2012, 04:27 PM)Ben Wrote: [ -> ]So it is just that they don't expand as much. Last time I asked the answer wasn't so decisive so I wasn't sure.
I know I will probably not have issues with a lifting head, but these would in theory make it a more reliable engine and would also mean it would be ready for bigger power in the future.
And Jake I will probably try and get a quote from them soon.
Stock bolts are stretch bolts so under high boost the stretch and lift the head. Arp are just high grade bolts so the don't stretch
![[Image: torque_failure.jpg]](http://engineeringfasteners.com/work/images/torque_failure.jpg)
Here is the best way to describe the difference in stock bolts and uprated one.
As you can see on the graph, the straight line between 0-100 indicates a linear tensile load/bolt stretch, as soon as the line starts to curve, then the bolt is being stressed to a higher load, but the extension is much more, causing it to yield, at this point, the bolt will not return to the normal length it started with if you were to release the load off it.
Basically uprated ones will be able to maintain the straight line for longer, meaning that they can be loaded more before they stretch, this being reusable and/or providing a higher clamp force. Stock bolts are designed to stretch past the yield point as thats where the maximum load on the bolts can be acheived, hence why we should in theory replace them, although I never have hehe, textbook tuners
edit: just realised this is a torque/angle graph, but the principles are applied in exactly the same way.
Thanks Dave. It really makes things easier to understand. Rep much earnt
Basically what Dave said, the high cylinder pressures tend to press up on the head and stretch the standard stretch bolts so they won't return to their normal shape afterwards - exactly the issue I was having...
ARP bolts don't fit as standard, be warned, you'd have to at least use 2 sets of ARP washers to make them work... If not 3 sets to get them in the right place....
Uprated bolts are basically made out of a very high grade steel - they won't stretch until a VERY high torque figure... They are heat treated and become quite brittle, but they won't stretch....
Had someone mention to me the old 1.6 205 gti head bolts weren't a stretch type (there was also stretch ones too on later cars) and should fit the xud.
Might be worth looking at?
Im looking into drilling them out to M14 and using cap screws
Getting them drilled and tapped to M14 may be a suitable solution, but you have to obviously get everything dead straight, and then make sure the heads honed out dead straight too. This is why it may be easier to get £200 ARP studs lol, when you're having issues lifting the head with those studs then M14 bolts may be applicable, but i've only ever seen ONE person have issues lifting the head with a turbo that dosent require SILLY amounts of backpressure.... con...
However, that was in an OEM k14 housing, which will have messed up the a/r... They're .42 as standard anyway from what I remember, with reaming that'll be even less....
Yeh so lots of backpressure hmmmm
ARP bolts don't fit as standard, be warned, you'd have to at least use 2 sets of ARP washers to make them work... If not 3 sets to get them in the right place....
What do you mean by this Ruan? Surely if you get bolts or studs made from a different material you could use them exactly the same as long as the threads correct? And why the 2 or 3 sets of washers?
Because ARP don't make them for the xud but they make some that will fit in the block but will be slightly too long in length
So instead of getting some that are perfect for 4x the price just spend the money on some longer ones and space it out with washers :-)
Ahh I see, what a simple reason.. I was over thinking it too much!