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Turbo guys: (Another) broken exhaust stud


Lebowski
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Ok, so I'm getting tired of breaking exhaust studs... today makes #3. I know all that weight of the turbo/manifold hanging out in mid air puts stress on the studs....

I spoke with Jon (the owner of 666 Fabrication who made the manifold) after the last stud failure and he didn't recommend any bracing on the manifold/turbo. I do remember talking to Pat Allen and seeing photos of his brace though so I'm re-thinking that plan...

Luckily none of the broken studs has sheared off inside the head so no oil leaks... I did reuse the studs that weren't broken though (also re-thinking that plan).

Does ARP or someone make hardened studs or is there something I'm screwing up? 15# of boost sure is fun, but as always there seems to be a price to pay for pushing things this far!

Note to anyone considering going turbo: It's these little things that kill you!

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Just a quick note... Coming from experience building high hp twin turbo motors, I would always fabricate some sort of brace to support the turbo manifolds along with installing better studs. Hks makes some great ones as well does greddy. Not sure if they have the proper size for an 02 but worth looking into. Turbos put a lot of stress on the studs as they spool up hence if you ever compared a stock manifol flange as opposed to a turbo manifold flange there usually is a good difference in the thickness. Oh and if you fabricate a brace I found it better to brace from the bottom of the manifold to the engine block. Just my 02cents and opinion

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I know I'm on the sidelines with this conversation But I'd like to add something.

The bracing from the bottom idea is good as it seams that a brace from the top is going to involve the valve cover or at least the head bolts. Bracing from the bottom could come from the motor mount plate. However when a turbo spools up and you go for that long 4th gear pull there is a lot of heat made and I could only imagine how much movement takes place due to heat expansion.

I guess the idea would be to brace, but leave room for some flex? Or instead of bracing to the turbo, brace to the manifold about an inch or two from the head. Let the manifold cary the weight of the turbo and let the brace hold the weight of the turbo/manifold combo. Then bolt to the head?

John

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Thanks for those pictures. Those are some crazy wheels haha. What are they?

Oh thanks! I hope that the drivetrain will handle 250. I think its reasonable.

Power to weight<3

Thanks Frenchee, they're Schmidt TH Lines, 15x7 front, 15x7.5 rear... one of my favorite all-time wheels. Glad you like 'em.

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I guess the idea would be to brace, but leave room for some flex? Or instead of bracing to the turbo, brace to the manifold about an inch or two from the head. Let the manifold cary the weight of the turbo and let the brace hold the weight of the turbo/manifold combo. Then bolt to the head?

John

John, I really appreciate the thoughtful response. I too was wondering about thermal expansion and the stress on the bolts after my last go-round. But that was with the old manifold, now the new manifold has an even thicker flange with more room around the studs to allow for some expansion. I guess I need to call and talk to Jon again to see his thoughts on bracing to the manifold. He has told me before that it shouldn't need it.. the manifold is strong enough to take it.

Maybe it's just all on me for using previously used manifold studs?

post-14664-13667632913803_thumb.jpg

post-14664-13667632916493_thumb.jpg

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do you know if they break because of thermal expansion of the manifold, or by vibration/harmonics from them motor ?

in all cases, there are simple fix for that...

if they break because of manifold thermal expansion (which would be evident from the picture above if it is made of stainless), one common practice is to place a piece of tube, and use a longer stud. This way the stud can flex more instead of snaping, as the manifold expands.

See my poor drawing. 3/4 inch -1inch of mechanical tube is good enough.

post-119-13667632921308_thumb.jpg

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If you are torqing the studs to the max when the engine is cold then the expansion of the manifold flange is going to over stress the bolt right at the time they are as hot as they can be when you are under boost. There is a reason the factory Turbos used 10mm Inconel studs instead of the 8mm steel studs on a NA M10 engine. I would use some kind of brace from the block to the turbo mounting flange and try a NEW set of studs and self locking Coper nuts, keep the torque well under the 25 ft/lb torque limit for a 8mm grade 10 stud. I would try something like 15 ft/lb to start.

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Depending on the material and design of the manifold you are looking at expansion measured in 0.001's of an inch. Compared to the strain on all of the parts trying to withstand the heat and vibration of the turbo, down pipe etc hanging off the head studs the worry about the brace not "expanding" is non existent.

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