ZX-Tex

iTrader: (15)

Yeah that is possible. But the bolt strength is ridiculous, like 15,000 lbs. I wish I had good numbers for the CTE of the turbine housing material Garrett uses but no luck finding them so far. I could run some calcs and check for the amount of load on the bolt due to temperature growth.

Laur3ns

Will fail according to my shop. I now have 304 stainless studs ready to go in and will report back on that next week. They use the same **** and are seeing 2000 F EGTs continues in 8-12 minute sessions. It doesn't fail.

ZX-Tex

iTrader: (15)

^^ Why do they think it will fail?

Laur3ns

12.9 or less, it doesnt like the high temperatures we see in that area. Not sure on the exact terms, but they become brittle.

spoolin2bars

iTrader: (1)

if anyone decides to go ***** out on the v-band setup, i have a new tial v44 wastegate for sale. $275 plus shipping. it's vband on in/outlet and has the flanges and all. lmk, thanks, john.

here's a few pics:

P090702002.jpg

P090702001.jpg

Laur3ns

If my stainless setup doesnt work I am going vbands now that Ive found some guy that will fab that **** up faster that I can break my studs.

JasonC SBB

How's the stretchiness of 304 SS?

ZX-Tex

iTrader: (15)

Lots of photos of beautiful, high-end (F1, CART, etc) NA and turbo racing engines here. See the top photos of the Ford Cosworth CART engine for some nice v-band ****.
ENGINE

304SS has about 55%-70% elongation at break. For comparison, A286 heat treated to 170ksi has about 17% elongation at break. So 304SS is MUCH more ductile, or 'stretchy', than A286. That makes 304 more tolerant to imperfections, cracking, etc. It is the typical tradeoff with metals, the higher the strength, the lower the toughness.

On the fence about whether to use a 300 series SS bolt, the Grade 12.9 hardware, or keep looking for A286. The first option is probably the safest bet, the second is more experimental, and the third is probably going to be expensive. For any of the options I still want to use socket head cap screws.

One thing to be careful of... I have seen stainless fasteners gall when used in stainless threaded holes. Sometimes it happens, sometimes it does not. In one case I had an #0-80 (very small) 316SS screw gall and completely seize in a 316SS tapped hole (in a very expensive prototype part) when I was just screwing it in by hand, no load on the fastener at all. I had to soak it in penetrating oil to get it out again.

But the screw and part were ultra, ultra clean, due to ultrasonic cleaning and a rinse with extremely pure alcohol. With even a thin film of oil on the threads galling is usually not a problem. But, on the turbine bolts, any oil residue will bake out. Maybe the resbond will help keep it from galling at that point.

curly

iTrader: (25)

I was going to say, the softer the better. Technically speaking you should never need a lock washer or loctite substance if a bolt or stud is torqued properly. By torquing it, you're stretching it and the elastic properties are what hold the nut from backing out. Of course all basic material theory goes out the door when dealing with the temperature's were dealing with. I believe the high heats and following cooling cycles we're putting our studs and bolts through are heat treating them. This makes them very strong, however takes away essentially all elastic properties. Once they loosen, and we tighten them again, they're not stretching, and therefore easily vibrating loose again. Starting with hardened metric hardware such as 12.9 would be a waste of time I'm afraid. I think you'll find that they'll back out faster than standard hardware, but it's hard to truly tell since putting them through similar tests would be difficult to say the least.

Some stainless hardware should resist this induction process the turbo puts it though, keeping their original elasticity. I'm not very knowledgeable on the properties of the different stainless alloys, but I believe you'd want a low carbon alloy with some magnesium in it, which ups it's resistance to temperature. Double check me on this by reading this here site:
Stainless steel - Wikipedia, the free encyclopedia

Laur3ns

No brittle rather, yes elastic gone. I think it's this effect: Sensitization effect - Wikipedia, the free encyclopedia.
Low carbon it is. The OEM exhaust studs look like they were made from some fany allow as they don't look nearly as bad as the studs I used to have in the turbo.

JasonC SBB

Re: SS galling. A recent Machine Design mag article mentioned about SS' propensity to gall, such that a graphite or moly based lube is a must when torquing.

minicoop821

Lock washers stopped that prob on my turbo civic years ago?

Laur3ns

Did you track that Honda?

y8s

iTrader: (8)

elongation at break doesn't help you... but a high elastic limit does. do you have data for that? or even better, fatigue limits?

Laur3ns

My manifold is back on, head surface was warped 2mm, now flat and mated. New exhaust gasket. New oem nuts.

Turbo is on, m10x1.5 304 studs, 15mm hex nuts. No resbond used anywhere. Downpipe has some old studs and two new 304SS, but that part is not the problem - has more studs too.

And now it's raining...

ZX-Tex

iTrader: (15)

OK just to be sure we are all using the right terminology here...

- Elongation at break is one measure of a material's ductility. It is not the springiness of the material.
- The Modulus of Elasticity (aka MoE or Young's Modulus) is the springiness of the material, or put another way, it is the strain versus stress properties. Think of it like a spring constant. For all steels, this is virtually the same, about 30 ksi, regardless of the alloy or heat treatment.
- The yield strength, loosely put, is the load a material can take before it no longer returns to its original length when loaded then unloaded. In reality, there is some microyielding at any load (even low ones) so the yield point is defined with an offset. But for our purposes the yield value is pertinent. Microyielding is more critical for very high precision parts.
- The ultimate strength is the load the material can take before it fails completely. This is also a little misleading since the load is actually increased by 'necking' as the part deforms, especially for more ductile metals. But, it is good enough for our purposes.

Any material will strain or 'stretch' some for any given load. Any steel will stretch some regardless of what steel it is, and any alloy bolt will stretch as it is torqued. The amount of stretch versus the torque load is a function of the MoE, which is about the same regardless of what steel alloy it is or how it has been heat treated.

If the bolts' tempers are altered by the heat cycling from the turbo, it is not becoming more or less elastic (the MoE is not changing). Rather its ductility is being raised/lowered and its yield (and ultimate) strength is being lowered/raised, respectively.

ZX-Tex

iTrader: (15)

Elongation at break is a measure of ductility. A more ductile metal (like 304SS) is going to be more tolerant of corrosion. That is one concern I have about the 12.9 fasteners; the lack of corrosion protection, combined with their low ductility, makes them more prone to stress corrosion cracking. So over time, they could corrode, have a crack initiate, grow (due to cyclic loading and corrosion at the crack tip), and then fail. It would be a long-term problem, say after thousands of cycles.

MIL-HDBK-5 has lots of fatigue properties for several of the more common metal alloys, and aircraft alloys. You can get a copy here. It is no longer 'active' but the properties it lists are still used by most everyone for design, including NASA.
http://assist.daps.dla.mil/quicksear...t_number=53876

Material properties are available at www.matweb.com

j_man

That's not a TB. It is an anti-lag device. With big turbo on a small 4 cyl. engine, it is used to keep the turbo spinning faster by controlling the intake/mouth size at different loads.

I am surprised noone has played with such on a Miata since that stuf has been out before the Miata was even made

JasonC SBB

Does this mean that studs can "break in" such that new studs need to be re-torqued a few times after a new installation?

Savington

iTrader: (31)

get the **** out of this thread