924Board.org

[chuck21401]

[Beartooth]

Thanks for all the input, lots to go on here. I wish I knew what material the Porsche bolts and spacers are made of. All I've found is that the under-head length is 37mm; I'm not even sure what length the spacers are. I can see where a lot of engineering comes into a system like this. Because of the amount of heat, you can't treat things statically: it's constantly shifting things, and will quickly fatigue the wrong materials. I might still bite the bullet on Porsche hardware for the turbine to housing, but I'm not sure the spacers (sleeves) are still available. Then, assuming they're available, $250 for the set is a lot to swallow. I'll keep my eyes out for a used set though; even if I go with ARP or whatever, it'd be good to be able to switch to if what I'm using keeps coming loose.

On the other end of the spectrum, there's the question of how to avoid bolts seizing. I'm pretty sure chromoly should be good with that. Fasteddie's experience makes me wonder about the OE bolts, but there's a good chance they were either over-torqued, put together dry, or both. I'm planning on nickel anti-seize on everything; the only thing (potentially) worse than bolts that come loose on their own are ones that would rather break than come back out. I got my manifold back yesterday; guess they had a heck of a time getting the broken bit of bolt out. $125 later... I'm glad I'm not looking for another manifold though. Come to think of it, that'd be another part that wouldn't hurt to have a spare of.
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1980 931 diamond in the rough

[Fasteddie313]

I believe I heard the Porsche bolts are titanium..


Manifolds aren’t super common to come by, especially not cracked..

Cracks can be welded though.. It’s a quite fun job
The weld itself isn’t hard.. It’s the prep that is an involved task..

The 941 has a flex section in the J pipe.. Pretty cool..
Also has stage 8 at least on the mani-head.. I forget about the rest of the nuts/bolts..
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80 Turbo - Slightly Modified

[Carrera RSR]

[chuck21401]

The rubber elbow connected to the turbo came loose again while on boost.



While I was trying to confirm what had happened, I noticed one of the bolts connecting the exhaust manifold to the turbo is backing out.

When I replaced those bolts, I used 2 ARP bolts and one Porsche $$ shouldered bolt. The Porsche bolt remains in place...so now I'm convinced that I should upgrade. Will be interesting to see if I can find them again.

Not the best picture...but this bolt is 1/2 way out.



The Porsche bolt hasn't moved. Also pictured is the hose clamp that broke loose.


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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler

[Cedric]

Did you end up using gasket or ring between the manifold and the turbo?
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1980 924 Turbo
www.instagram.com/garagecedric/

[chuck21401]

[Beartooth]

I used ARP chromoly bolts when I put mine back together, but drilled them for safety wire. I'm finishing up a bunch of other stuff and have barely run it, let alone driving it, but the plan is to torque the bolts, drive it a bit, then re-torque and safety wire. It's gonna be a PITA to do that, but it should be doable. I'll report back on how it works out. I wouldn't call it better than the OE bolts even if it does work, but the bolts alone would cost over $100 and you'd need to find the spacers somewhere (they're NLA, I couldn't even find an exact match in chromoly - not that you'd use that with Ti bolts - and so I figured the ARP bolts were worth a shot).
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1980 931 diamond in the rough

[Cedric]

[chuck21401]

It looks like both parts are NLA. (edit: in the US)

On the hunt, maybe I an find used a used set or two.

Edit: These are available in Europe as of June 2023. Ordered two sets from Rose Passion in France. Shipped quick, arrived after 5 days via DHL.



Bolt 93112319700 and Sleeve 93112319900
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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler

[Beartooth]

Well, I'm revisiting this because I've already run into trouble with the ARP bolts. I'd run the car a few times after getting the turbo back in last fall, then it sat until I finally got it going again a week or two ago. I'd only driven it twenty miles or so when I decided to check the bolts over and safety wire them. Two of the three bolts came out just fine, but one of them broke free, then bound up in less than half a turn. I sprayed in some penetrating oil and worked it back and forth until I was able to get it out. Somehow, about half a thread got torn off. I'm assuming the top threads in the manifold got damaged too, but I put a new bolt in, and it went in fine.



Now I'm wondering if I should be looking to Ti, or if whatever Porsche used is the only thing strong enough and that won't gall threads. I'd considered stainless, but what I read indicated that it's actually more likely to gall the threads than chromoly. I read in a couple places that chromoly should work fine (and be less likely to gall than stainless), but not a good sign here unless there's some freak thing that caused this. At that price of the OE bolts and bushings, I have to wonder if there's some secret sauce there. It looks like the bushing at least would have to come over from Europe; most US sources list it as NLA. Then it's $200 for the hardware set... I'm not sure about a substitute bushing, even in Ti, I'm not seeing anything off-the-shelf that'd work, and using a different material would probably be self-defeating anyway. That said, if anyone has a bolt and bushing set they'd part with, let me know.

One intriguing option is to use Ti studs. Those are readily available (usually in sets of four, I think intended for a T4 flange), and I'd think I could drop a set right in. I know studs are usually preferred where practical (and accountants aren't involved), but I'm not sure if it'd be the ultimate step up here, a lateral move, or maybe even a step back. I also wish I knew more of the thinking behind they way Porsche did it - if there's much to gain from copying that as much as possible, or if there's not that much too it. I realize I may be overthinking this, or maybe being cheap by not just buying the OE hardware, but when there's a $75 solution that may be as good or better than the $200 solution, it's hard to pass that up. And of course, a hardware failure here could mean lots of headaches...
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1980 931 diamond in the rough

[Beartooth]

I have a potential answer to my question. I'd bet Carrera RSR is right that the Porsche bolts are inconel (or something similar). Doing a little reading, it seems inconel is the go-to for this type of application: corrosion and heat-resistant and fairly strong. Titanium might work, but it's quite a bit weaker than inconel. Anyway, I can't find much for an alternative inconel bolt, but there are some options for inconel stud kits. I see this one listed several places: https://turbosource.com/products/inconel-turbo-stud-hardware Unfortunately, it's not the absolute best: it uses A286, which is closer to stainless steel in many ways. But it may be a good choice. Another option for studs, apparently, comes from Mazda: the RX-7 uses M10x1.5 inconel studs. I've also found a couple small-time aftermarket turbo kit suppliers who have custom runs of studs made by ARP (no less), but availability isn't good...

I'm not sure I should pull the trigger yet, but I'm leaning that way. I'm pretty sure I could install the studs the turbo in place, but I'm not sure about getting it apart again. The ideal thing would be studs with an allen head, and I'm not sure if any of the ones I've mentioned have that. Still, I don't think I'd paint myself into too much of a corner. I'll have to think about it and eyeball it over the weekend; for $50, it at least seems worth a try unless disassembly would be a big problem.
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1980 931 diamond in the rough

[chuck21401]

I think it's interesting that Porsche moved to collar bolts/spacers along with other modifications mentioned in the technical bulletin issued in 1983 (Group 21, Number 83-03).



This note is on page three of the technical bulletin.



No doubt the bolts/spacers are crazy expensive. But I am glad to see that they are still available, 40 years later.

I still need to get under my car to swap out the third bolt...probably while I'm there for the next oil change.
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1981 Porsche 931 w/S1 engine & g31 transmission. Water-cooled intercooler

[Cedric]

Regarding materials, OEMs might use metals closely related to inconel in their hardware, one reason i use the Scania bolts is because i know what they are made of
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1980 924 Turbo
www.instagram.com/garagecedric/

[Beartooth]

If the cost were the same, or at least close, I'd go with the OE pieces - it's just hard to pull that trigger when 1) They cost 2-3 times what should be as good a solution (inconel or other super-alloy studs); 2) The bolts may have a tendency to back out (there goes $70); 3) Studs should be stronger and clamp better. I can't find much on any applications that use a bolt and collar like Porsche did here, and I'm not sure what to make of that. Obviously, there are reasons they chose to, but it's not apparent, and it doesn't seem any aftermarket builders use anything other than studs.

I'm not set on that kit I linked to: it's titled "inconel stud kit" then goes on to say it's something other than inconel, and I also have to wonder if it's China junk. That said, assuming it's well-made, A286 would probably do the job (used in some gas turbine applications), but seems to be a low-cost alternative to some degree. I have heard good things about the Heico-lock washers in that kit - that may eliminate the issue of the bolt backing out. It's still noteworthy that Porsche used a bolt and collar setup: I see a lot more recommendations for studs, and I wonder if that was stronger somehow, or had to do with making it easier to get apart.

I do agree with you Cedric, that OE hardware is a good choice. With regard to the stud option, the RX-7 studs are a really good deal for what they are. It's not going to be the highest-spec thing there is, but given that it went on something that came with a warranty, it's gotta be good stuff. I just wish there were an option from a name like ARP, but it seems like there's nothing at that level in inconel (or similar super-alloy) outside of having it custom made (at outlandish prices).
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1980 931 diamond in the rough