I got these studs which have a Minimum Tensile Strength of 124,000 psi
McMaster-Carr

Matched with stage 8 10mm locknuts
Flyin' Miata : Turbochargers : Parts and upgrades : Stage 8 locking turbo hardware (10mm)

Now, for the track guys/engineers or anyone who can shed some insight.

I am going to guess that now my begi cast mani is the weakest link here. My question is, how are the threads inside the mani going to hold up? Will i be screwed from having the stud shear the female threads? I will of course re tighten them after they heat cycle a few times.

If this doesn't work, what will?

Since everyone like pics, here is one i mocked up while i await my motor to be completed:
IMG_0445.jpg

 

I would say that on the street you are fine. On the track this 10mm stage8 will still loosen or break. The manifold should be ok as that has 9 nuts over 4 here. That is 125% MORE nuts.

 

My apologies for not making this clear.

On track, will this hold up? I am talking about the studs threaded into the mani. Not the studs on the head holding the mani to it. Think the stage 8s aren't strong enough?

To make this even more clear, the 4 studs in the picture above.

 

@thesnowboarder: I have not tried stage8 myself but others have reported that nothing holds up at the track once you drive hard enough.

 

remember that the studs (when tight) are primarily in tension. there is very little shear on them. the shear force is carried by the material interface of the manifold/turbo mating being squeeeeezed by the tight studs. so as long as they stay tight, they wont shear.

i think the stage 8 hardware will be fine. it's in a low load situation other than the nuts themselves, right?

 

The problem is not lack of strength, it's that they loosen, which the stage 8 stuff will address.

 

All,

I just tried the Stage 8 system on a Miata Turbo over 4 track days. The nuts remained on the studs (M8 1.25). However, the studs stretched/backed out themselves. Tension was lost. So, at least I didn't lose the nuts and the fancy retainers, but the I could rock the nuts back and forth about 3 degrees with my finger (once things cooled down). These were fancy-pants ARP exhaust studs, by the way, that promised a tensile strength that "far exceeds grade 8 bolts."

These Stage 8 fastners did keep a small exhaust leak between the turbo and manifold from becoming a big exhaust leak. However, even after retightening when warm (just try to get the locking hardware off of a hot turbo sometime. The lower right nut, ouch!), the nuts still lost tension the next day after a single 20-minute track session.

I was still making full boost, and the gap shrank when warm, but I could have slipped a feeler gauge in there when cold.

So, even though these worked, the stud to which they attached still let the overall system fail.

Phil


Has anyone tried simply welding the studs in? Or using high-temp epoxy? Anyone?

 

I have a begi s5 manifold.

I've had the same problem with studs backing themselves out. I tightened down the locking nuts on the studs really hard but the stud still backed out. The nut didn't move at all. This was with street driving.

I too would like to know a way to keep the studs themselves from backing out.

 

Drilled studs with a castle nut safety wired.

MX-5 Miata Forum - View Single Post - Calling Black Jesus...

 

Thanks for the link, but I don't understand. Wouldn't this just lash the nut to the stud and keep the nut from coming loose? The only way I can see this working is if you're lashing a nut onto both sides.

 

The stud is drilled, you safety wire the studs, it keeps the studs from spinning. The castle nut allows the safety wire to pass through, also retaining the nut.








I assumed it was implied, the cotter pin mentioned is not used, you replace that with safety wire.

 

I dont know if you have room, but i use 3/8-24 nut and bolt. been on there for almost 2 years and have never messed with it since. There not even anything fancy maybe grade 5. or go 7/16 NF, but again you may not have the room for that size bolt/stud.

 

How much track time?

 

2 days @ Streets of willow and 2 days @ Spring mountian in NV. and 13K miles on the street. would like to track it more often, but the economy is not allowing it.

 

What are you using to keep the nut on?

I agree a larger size with more thread area is needed for most of us. But I think your setup will eventually loosen.

 

The nut itself is an OEM exhaust nut, i cant remember for what car, but i will find out for you all, its just been so long since i put it on. Anyways I remember the threads inside the nuts have a little wave in them right at the end so they go in a bit tight at the end of the nut. Basically they spin on real nice then when you are tighting the nut it kind of feels like your cross threading it cause it get tight, but it does not cross thread.

 

Opppss, correction i have a 10mm x 1.5 nut and bolt, not 3/8-24. holding the turbo to manifold. My mistake. The nut from what i gathered from everyone i ask said they think it was most likly porsche 944 turbo, but that may not be correct. obscure details, when it happened so long ago. dang it :(

 

safety wire. I saw it on a few cars last weekend, but v-bands are the answer. I'm going to try the safety wire and if it fails I'm getting the check-book out and getting a tial turbine housing w/gate, begi s4 manifold and dp with v-bands and never looking back. Gotta pay to play. There's a reason every car in competitive racing runs v-bands.

 

hustler, you gotta figure out how to do v-bands on the head flange.

 

Nah you can use explosive welding to join aluminum and steel so just do that for the head-to-mani joint