Richsubarusti

Just wondering what power some of you are running with 11mm arp head studs at what boost level ? And at what stage would you need to go for the bigger studs .if anyone has some for sale let me know cheers Rich

Tidgy

mines built for a 500bhp daily 2.5, currently running low boost untill i get a few other supporting mods, but im on 11mm's

WUZ

iTrader: (14)

Anything over 1.6 Bar or 450bhp and it would be prudent to run a 14mm Head stud on a 2.5 build - you are talking about a large amount of force on the combustion chamber with a 99.5mm (or larger) diameter piston!

Richsubarusti

Would it be about the same bhp and boost level for a 2.0 sti before going for the 14mm studs ?

Tidgy

Mine will be well over that so that's not the case.

domino46

no offence intended but yours "will be" doesn't prove anything lol ,,, proven specs for over 500bhp on a 2.5 normally include 14mm head studs and thats a proven fact not a WILL BE

iv heard mine will be this and mine will be that so many times and seen many of them fail so best to get over the 500hp mark before making claims in my view ,, but remember heads dont always lift strait away so again proof is in running it for a while not just doing a few dyno runs and then running around on low boost lol

mines still going strong after 5 years in my ownership running over 500hp and the new owner is loving it aswell after nearly a year so the 14mm conversion is worth doing to cross any risk off ,,, iv had quite a few big builds done now and 14-14 stud conversion is always on the list lol

johnlogie

iTrader: (4)

2.1 SCDB, 11mm ARP studs, approx 500bhp, 1.8 Bar boost. Built in 2013, done about 15,000 miles. 8,000 of them at 400bhp, 1.65 Bar, last 7000 at 500bhp. Obviously the majority of the time it’s running at low boost but I have done quite a few track days. No issues at all.

WUZ

iTrader: (14)

Had you read my post you would have seen the words "it would be prudent"........ try grabbing a dictionary when you get the chance and learn something new about the word prudent.........

Pulling apart a 2.5 engine in its entirety and getting the machining work done to the block for the bigger RCM 12mm stud or the block and heads for the big daddy 14mm studs from Alyn or RCM is very time consuming and expensive so if you don't decide to do it at the point of the original build.

Chances are (based on real world experience of 100's of 2.5 builds on here) that by the time you have put 16-20k miles on the block (+/- 2 years of ownership), your heads will have lifted or be about to..........

2.0's and 2.1's have APPROXIMATELY a 15% smaller piston diameter so you would need more boost on a 92mm piston to match the force on the heads similar to a 99.5mm piston.

In short, on a 2.5 build - err on the side of caution and future-proof the build with 14mm studs - its not about power, its about compression ratio and cylinder pressure. 2.0 Bar on a VF 48 will lift the heads just the same as 2.0 Bar on a GT35....... power difference is +/- 180bhp

domino46

still doesn't really prove anything as its a 2.1 ,, we all know what the 2ltr block can do as its been done loads of times by many people ,,,,,one of my close mates is running over 800bhp and around 2.4bar but again thats a 2ltr block with 14-14 studs,,, iv ran 2.2bar in my 2.1 with 14-14 head studs but that still doesn't mean anything when relating to the 2.5 really lol

johnlogie

iTrader: (4)

the OP in post #4 asked about 2.0 ltr block so I think my post is perfectly relevant. The OP hasn’t mentioned the 2.5 block in any of their posts

domino46

apologies didn't see that bit

johnlogie

iTrader: (4)

No probs mate

MOTORS S GT

iTrader: (2)

Nobody is stating which 11mm Arp studs they are using, the 180,000 psi or the 260,000 psi, quite a big difference in the final clamping load.

adam.pah

There are 2 versions of the ARP 11mm studs. If you are referring to the standard ones, then I contacted ARP last month to find out what they recommend boost wise. They stated that they don't have an official recommendation although 20-25psi should be 'safe'. They said that if I wanted to go more than that then they recommend using the high performance 625 version. I did just check to see if I still had the email but I must have deleted it.
On my 2.1 I am currently running 1.75 bar (~25psi) which seems fine. I could probably run more and it would also be fine....until it isn't! I'm told that these things aren't an exact science as it can depend on lots of other factors so I decided to stick to this 'recommendation' while also using good MLS head gaskets.

John 37

RCM offer 2 types of 11mm studs. They say they're suitable for 350 & 450 bhp.
The arp ones look slightly stronger.

stockcar

RCM very much err on the side of safety and their "std' studs have been used many times at 450'ish

personally once your above this level then its a no brainer to go 14mm given the 625 option is more expensive even including machine work