ARP vs Stock studs

[sempaipaul]

Guys,

Currently going through a full top and bottom end rebuild. Trying to figure out whether to buy OEM studs (head studs, connecting rod studs) or, whether to spend a tad bit more and get ARP.

For the head studs - what are my choices. I hear a lot of Dilawar studs and the controversy that surrounds all of the OEM studs. I am looking at these ARP head studs: http://www.amazon.com/ARP-204-4206-Head-Porsche-911-930/dp/B0057Y7A48

For the connecting rod bolts - what are my choices? I am looking at these ARP units: http://www.amazon.com/ARP-204-6003-Connecting-Rod-Bolt/dp/B00IKAEWFG

Also - I came across this engine case kit from ARP. Would this be a good investment or, is factory stuff more than sufficient? https://hinsonsupercars.com/p-20216-arp-504-9501-porsche-911-930-turbo-case-stud-kit.aspx

Not doing anything crazy with the build --- 79 SC 3.0 with CIS and going to 964 cams and higher compression pistons 9:5.1

Look forward to hearing!

Regards,
Paul

[chris_seven]

This question keeps going around and around.

Standard steel studs on a standard Alusil engine case should be just fine.

Rod bolts don't seem to fail but use new nuts.

If you use ARP Rod Bolts you will have to re-size the big ends as well.

[Alan L]

I got ARP head studs - and then some engine builders on this forum tell me they won't use them.
Rod bolts yes, but studs no. Supposedly come loose (at the heads) - but I can't verify that.
Alan

[Flat6pac]

I don't know why so many think that ARP is the Golden Fleece for rebuilds. At least one person has the heads come loose and posted here. If you're going to upgrade the head studs, look at the supertec units with the fine threads on the outside for better adjustment of torque much like the factory uses on the through bolts from 3.0 on. The last several mag cases I built I used the the fine thread through bolts for better hold and torque adjustment. The factory items are sufficient for street building.
Bruce

[chris_seven]

One of the main issues with aftermarket studs and magnesium engine cases with aluminium cylinders is concerned with the core diameter (shank) of the stud.

If the core diameter increases then the additional force created due to expansion can be a real problem.

The force generated by expansion can accurately be described as irresistible and for a given Young's Modulus (E) is proportional to the square of the diameter.

If you increase the basic stud diameter from the 7.6mm of the standard stud to around 9.5mm then the pull our force generated will be 1.6 times that of the standard stud - something I would try to avoid on a magnesium case.

I can't see why an ARP stud should come loose at the head unless they are fitted without thread locker.

I realise that ARP suggest installation without the thread locker OR that the studs should be torqued before the thread locker sets which would be a real pain without special tooling.

Bottoming a standard stud into the hole in the case is not wise as this will cause issues with uneven loading due to the poor quality thread at the end of the blind hole.

The optimum solution is to use a stud with a 'dog' point that can bottom into the hole avoiding the poor threads and allow the stud to be torqued to about 12 lbsft before the threadlocker cures.

We have been making Titanium Studs with this design, specifically for Magnesium engines for about a year.

The Ti also has a lower modulus so that the increase in 'pull out force' due to expansion also reduces.

We use a fine pitch at the head end but this is so we can use a 928 - 12 point con rod nut which has a much lower cost than an ARP 12 point nut. We also make 17-4PH stainless steel ground washers.

The end of the stud is broached to allow them to be installed with an Allen Key.



We have them in around 10 engines so far and they seem to work well.

[Lapkritis]

Memories. ..

I have the arp but lust after a set of Chris's titanium. Next rebuild perhaps...

[jdbunda]

Originally Posted by chris_seven

This question keeps going around and around.
If you use ARP Rod Bolts you will have to re-size the big ends as well.

Chris - I am about to build my bottom end with ARP rod bolts. I was unaware that any "re-sizing" needed to be done - exactly what are you referring to here?

[boyt911sc]

I've done a few SC engine rebuilds using ARP rod bolts and not been aware of this process (?). Could someone elaborate on this subject. Thanks.

Tony

[Alan L]

Tony - as far as I know the 'issue' is with the head studs. There is a discussion - I think in the 930 forum recently (last 3-4 weeks) on this issue. The rod bolts apparently are rock solid.
Regards
Alan

[boosted79]

It's always a good idea to get the rods rebuilt whether using OEM bolts or ARP. The shop shaves a little off the cap mating surfaces, installs the caps using the ARP bolts or the original bolts if using OEMs then hones the big end to spec. Then they install new bushings and hone the small end to set both the center to center distance and pin/bushing clearance. If you're reusing the pistons/pins they'll want your original pins to size the bushing or a new pin.

[J-Mac]

Paul

I think the ARP rod bolts you need for a SC are 204-6005 and not the 6003 version you posted.

[Henry Schmidt]

We have sold over 1200 sets of Supertec head stud kits to over the last 12 years and to date have had ZERO complaints.
It is the number one selling head stud kit on the Pelican Parts website.
They are used by professional engine builders and DIY enthusiasts for both street and racing application.
They are selling so well that we are struggling to keep up with demand.
I notice the Chris has copied some of our unique design features to make his titanium studs which is indeed quite flattering.


Supertec Head Stud Kit

[chris_seven]

Henry,

I don't think you can call using a different thread pitch in order to use a much lower cost 12 point nut copying.

If the 928 con rod nut had been a standard Metric Coarse we would have used this thread pitch.

The best price I can buy genuine ARP 12 Point nuts in the UK is $6.00 each and I pay $2.00 for the 928 Con rod nut which is nearly 100 bucks difference for an engine and worth saving.

Which other features do you believe we have copied?

The material we have selected is different.

The shank diameter is different

We have added a 'dog point' and broached the end to allow installation with an Allen Key.

I would accept that the case thread is also the same but this is not really an option.

I had no intention of copying your design and as we only use these studs 'in house' I would hope it doesn't become an issue but we will consider using a different nut in the future. May be a prevailing torque silver plated K nut would work. I will buy a batch and check them for variation in running torque.

I hope that doing this won't offend Casper Labs who also use a prevailing torque nut.

The use of a fine pitch in stead of a coarse pitch is interesting as an exercise but I am not sure that the torque/preload levels used in 911 head studs it has much practical significance.

It is true that a finer pitch will have a greater mechanical advantage than a coarser pitch and that for a given torque the preload will be greater but the increased friction created by the longer thread length will tend to reduce this effect.

In practice if would look at the increase in axial load created by the geometric difference and then factor in the increase in friction the difference in 'one pitch' size is less than 5%.

If we then consider that preload using simple torque control, even in a perfect world, is likely to vary by 25% then the differences can simply be neglected.

It is fair to say that the stress in the nut will be lower with a fine pitch but at the torque levels being used I think this is irrelevant.

It is also fair to say that the fine pitch is also more resistant to shaking loose but again I am not sure if this is a major issue.

The subject of ARP nuts coming loose is interesting and worth some consideration.

In general it would b difficult to determine if the nut has simply shaken loose or if the stud had come loose from the case if ARP's recommendation had been followed and the studs had been installed without thread locker.

ARP also suggest a higher torque figure and if this is used in a Magnesium case the extra preload could cause stress relaxation to occur in the case and this would reduce preload and allow the nut to loosen.

With regard to con rod bolts ARP recommend that rods are re-sized after new bolts are installed as it is possible that the increased preload in the bolt may cause the big end to deform slightly and this could cause a bearing to pick up and will affect crush heights.

Just swapping fasteners is not always a great idea.

We are also in the process of designing a replacement Case Bolt set. We are planning to use a Tie Rod which will also prevent 'shuffle' by effectively pinning the engine cases.

[Lapkritis]

Originally Posted by boosted79

It's always a good idea to get the rods rebuilt whether using OEM bolts or ARP. The shop shaves a little off the cap mating surfaces, installs the caps using the ARP bolts or the original bolts if using OEMs then hones the big end to spec. Then they install new bushings and hone the small end to set both the center to center distance and pin/bushing clearance. If you're reusing the pistons/pins they'll want your original pins to size the bushing or a new pin.

Watch for oem fracture split rods though as this technique would ruin them.

[Henry Schmidt]

Originally Posted by chris_seven

I had no intention of copying your design and as we only use these studs 'in house' I would hope it doesn't become an issue .........edit.......

Good morning Chris
There is no issue at all. Like I said, "it's flattering".
There are many companies attempting to make a replacement for 911 head studs and competition breeds innovation...If you design a better head stud that is also cost effective, I may even use them. After you have two or three hundred sets in hundreds of engines with 100,000+ miles of success, let's revisit the question.

I appreciate these head stud discussions on forums throughout the internet because EVERY time they occur, our market share increases. Head studs are almost meaningless to our bottom line but my ego appreciates the validation.
Cheers

[Flieger]

I have to say, I don't see anything I'd call copying taking place. There are loads of other Porsche products which clearly get copied but these parts seem quite different to me, or at least as different as fasteners for a specific application can be.

Has anyone thought about making cylinders like an aircraft engine where they bolt to the case and then the heads bolt to the cylinders?

[boosted79]

"Has anyone thought about making cylinders like an aircraft engine where they bolt to the case and then the heads bolt to the cylinders? "

Make the cyl. and head all one piece like the old P&W radials. Just have a bottomless check book.

[Flieger]

Originally Posted by boosted79

"Has anyone thought about making cylinders like an aircraft engine where they bolt to the case and then the heads bolt to the cylinders? "

Make the cyl. and head all one piece like the old P&W radials. Just have a bottomless check book.

Well, Porsche did weld the heads on to some of their turbo motors- 962 I think and Moby Dick. I figured that if LN Engineering can manufacture the Nickies they might be able to do something like a Lycoming cylinder.

[Reiver]

Originally Posted by chris_seven

This question keeps going around and around.

Standard steel studs on a standard Alusil engine case should be just fine.

Rod bolts don't seem to fail but use new nuts.

If you use ARP Rod Bolts you will have to re-size the big ends as well.

Chris, in your opinion, how about steel studs on a 930-10 204 hp Euro with Nikasil?

[chris_seven]

We use standard steel studs on Aluminium SC cases all the time and have done for 7-8 years and never had a problem.

The 'class' of thread on a Porsche supplied stud seems better than any of the aftermarket studs when checked with typical 6H go/no-go gauges so the 'rock' a little less when fitted.

This is the main reason we only use our Ti Studs with Magnesium cases which are more prone to
suffer fro stress relaxation and pull out the thread.

I worry about Dilavar because Precipitation hardening Austenitic Stainless Steels to tend from intergranular corrosion in the presence of chlorides and I am not sure how long the coating on the latest 993 studs will last.