I don't want to drag into a long winded post so I'll keep this simple.

M96.70 engine being built for a roughly 700hp 996. Not my first build by far but first using this ARP headstud kit (PN 204-4210). Studs are coming up too short when installed into the case. Can only get about 1.5 turns of thread engagement on the nut(need about 6 minimum). Studs are of a bull-nose design, which typically in other manufactures and other applications goes INTO the case to bottom out in the stud register and provide a positive stop for the stud, however ARP techs are telling me it goes out.

Threaded in, the studs have inconsistent heights due to no consistent stop for the threads in the registers. Flipped around with the bullnose in the case I get more thread engagement at the nut(about 4 threads) but still not completely through the nut. Moreso, doing it in this fashion only puts about .5" worth of thread length into the case to secure the studs which can't be enough in an aluminum housing under this type of stress.

If one installs the studs according to ARP specs, but only threads them into the case just enough to get the full 1" of thread engagement at that end of the stud, you STILL end up falling short on the nut and then have to deal with stud rotation while tightening the fastener nut, let alone torquing them.

Has any engine builder here dealt with this issue on this particular application? Am I just being too picky with this crap ??? I cannot imaging how ARP designed this with the shortcomings the studs have.

Stud registers are ~1.735"from case deck with thread starting ~.36" from case deck. Fully installed(per ARP specs) studs protrude from case deck 6.067", some +/-.100" or so.

The build is currently on lockdown until I get some solid answers from ARP, or until I can get ahold of Kevin @ UWM and chat with him about this.

Big thanks folks. Nice site here, apologize for dumpy a crappy post as one of my first(if not the first) post.

 

This probably means nothing, but I saw it on the description for the studs at vivid

You will also note that ARP offers specially undercut studs for several engines. This procedure (done only to the shorter studs) more equalizes the "stretch" of both studs, which makes for a more consistent clamping force - and one that compensates for head gasket compression when the cylinder heads are installed. This helps prevent blown head gaskets, and assures optimum engine sealing!

 

Big thanks to Ian @ Evo MS. Had a good conversation about the issue and ordered up the last set of their studs they had in stock to replace this defective useless pile of bolts here.

~$700 price difference between the two sets is not worth risking potential multiple thousands of dollars when(NOT IF) they fail.


Now to deal with ARP and get a refund for the customer on these

 

Good choice. My engine fell apart with those ****ty ARP HS. Go with EVOMS. Are you doing the 12mm or OEM replancements?

Jag

 

OEM 10mm. Car has twin Alpha A28 billets, ~1.6 bar of boost. Made 599.89 AWHP last year before bending stock rods. Setting up and tuning for E85 after the motor breaks in(Tony @ EPL did before/still is tuning the car).

 

Sorry just seen the post.. Raceware... You would have saved a bunch and I have put 30 psi of boost on them with stock head gaskets no problem.

 

How much AWTQ and at what rpm did the car make before bending rods? What aftermarket rods are you going with? Just curious, thanks.

 

bent rod are very common on motors running over 1.2 bar with stock rods.

 

dont know what about turbos or fuel rod bend at 1,2bar?...but with 93oct and most hybridturbos no problem till 1,4bar for my understanding

 

Yes, was a stock motor running 1.6 bar on Tial turbos. Bent the rods causing one to slap the counterweights on the crank. That particular rod forced the piston pin over and popped a circlip out, which caused the pin to ride the cylinder wall and score the bore up.

New motor for customer has Carillo rods, new crank, JE pistons with full options(FSR forging, skirt coating, dome coating, hard anodized first ringlands). New OEM bearings, WR gasket kit, etc, etc. Customer is looking to setup and retune on E85, but not until The motor is properly broken in.

Ordered a set of EVO MS headstuds. Just waiting for them to arrive.

 

1.6 bar on TIAL A28S ( probably on pump) is not good... we don't go over 1.2.. and usually 1.35 on race.. thats it...
A28s are Torquee... TQ bends rods not HP...
But then it can happen to anyone...

 

Car was 93 + meth. Tony @ EPL tuned the car for the customer. I do no tuning..... just fab/protoype work, engine rebuilds, and occasional installs of aftermarket parts.


A28's are definitely torque monsters. Rods were the weakest link in the system and bend. Now I fear for the Viscous

 

Here's the dyno sheet of the car prior to the engine failure due to bent rods

 

As you can see its producing globs of TQ down low... although everyone would love to have that TQ but once things go bad they all wake up... notice that most guys with bigger turbos like 30rs do not bend rods... just lift the heads form running too much boost...
I am scared running smaller turbos past 1.4 bar on 100/104 octane.. but thats just me...
alos, looks like OEM piping to turbos and or slightly restrictive exhaust... car is choking up on top...

 

Stock IC cores, charge piping and Y-pipe. Fabspeed turbo inlet system, stock(non-ported) turbo manifolds, AWE straightpipes. I am making a new 3" exhaust for the car to quiet it down a bit as the straight pipes are abusive on a daily basis.

I agree with the fact that it was these turbos that initiated the bent rods. I told him that, and that the drastic increase in low end torque meant the system was overloaded down too low. Something had to give, rods being the weakest link they went first. He had mentioned the possibility of going with larger compressors, but then he also talks about selling the car after this is up and running so who knows really.

Just makes me wonder what'll be next down the list, but I have a sneaking suspicion the viscous coupling is the next target.


As of right now though I have to find someone with P-tool 9661 to time the camshafts. I owned the tool at one point but had a multitude of stuff stolen from my shop and wasn't covered by insurance that at time. Either that, or I need to find/verify the stock camshaft timing via lift @ specified crankshaft degrees and degree the cams as though they were aftermarket.