There are numerous stainless steel alloys (alloy = mixture of base metals) available. Not all of them offer heat resistant properties. Would be nice if you could find out which particular alloy this is (available on ARP's website perhaps?).

Don't forget that exhaust manifold studs in the head can get away with less heat protection because they are water cooled. The studs in the manifold to turbo and turbo to downpipe connections only get air cooling, with the manifold to turbo being, by far, the highest heat connection in the car.

Well, I still need to call that fastener place listed earlier, but so far, it looks like the BEGI 8mm inconel downpipe studs are the only "good" option.

Miata Downpipe Mounting Hardware - Inconel studs /8mm BEGi

$175.85 + $18.64 Shipping. Fuck that.

Also - I have been fighting removal of my turbine housing from the CHRA for days. I finally got it off, but some of the turbine housing to CHRA bolts are a bit rounded.

Are these special material too?

I think Hustler wrote about his CHRA bolts over in the EPIC thread. Thankfully, my Mitsu turbo uses a V-band for that.

It looks like Ford uses M8 studs for 4.6 and 5.4 V8 exhaust manifolds. At some point furing production they switched from standard steel to some sort of stainless alloy to try and cure stud breakage.

Ford 9K494SUB Exhaust Manifold Install Kit 8 Studs Washers Nuts | eBay

Looks like you can get a full set of 8 studs, nuts and washers for pretty cheap. Not sure why the studs have a copper color though.

Also not sure what type of stainless they are made from. But, I might try these instead. The local parts store (O'Reilly) had a set of these studs in the "HELP" section. Of course the HELP ones are shitty chinese brand, so I didn't buy them. Length is 56mm.

Well, after removing the TSE inconel studs that came with my manifold - it looks like one of the threaded holes in the manifold is boogered up. It has only about 20% thread height on one side.

I'm not sure if this happened before the previous owner installed the TSE studs or after. No way to know. In any case, it looks like I will have to fix this somehow.

So - on to the question. Should I use a Time-sert (unknown material), or an Inconel 725 Helicoil?


Versus:

Helical Thread Inserts: M10 x 1.5, 15.0mm (1.5xD) Length, Free Running, Inconel X750 (Package of 1)

I'm kinda leaning towards the Inconel helicoil. It is cheaper as I already have a helicoil installation tool, and I only have to buy one (probably 2 to be safe) inserts. It is Inconel, so should be plenty strong at high temps versus the unknown quality of the TimeSert at high temps.

Any thoughts on this?

I agree with you. I would go with the known material that is suitable for the temperature requirement.

Time-serts- I've never seen many good things come from heli-coils. Never known of inconel ones, but never liked heli-coils for anything important. Brackets-maybe. Sparkplugs and such-no.

I did a little more research, and it looks like a standard Time-sert insert is just carbon steel.

http://www.timesert.com/html/12L14CarbonSteel.pdf

You can special order them in 303 stainless as well.

That being said, it looks like neither 303 or carbon steel would be recommended for high temp applications. It's looking like Inconel is the better solution.

For what it's worth - I have never had an issue with Helicoils in the past. I've used them for motor mount holes into an aluminum block - which should have some pretty high load and vibration. Seems like Helicoils don't work very well for headbolt/stud applications though.

One of my cast manifold stud holes is helicoiled.

I know this thread is a month old, but I'm going to resurrect it with what I'm sure will turn out to be a stupid question...

I'm seeing turbine housings with studs and bolts in various locations. Is there a reason to use studs over bolts in specific holes, or is this an OEM packaging thing? Why not run all studs? Or all bolts? :confused:

Actually, a pretty good question.

Speaking from personal experience:

Bolt:
1. Cheaper (1 part vs. at least 2 parts)
2. Easily drilled for safety wire
3. More prone to getting frozen due to corrosion -- a definite consideration in a high heat environment
4. Requires enough clearance around hole to insert the bolt

Stud and Nut:
1. More parts
2. Both stud and nut need to be secured -- you'll end up using things like high-heat thread lockers and stage-8 fasteners
3. So long as you never want the remove the stud, the only corrosion/freezing you care about is between the stud and nut -- usually easier to control
4. Handles situations where clearance to insert a bolt may not be present

In my case, Inconel studs on manifold to turbo and Inconel bolts on the downpipe seem to be working just fine. Of course, I had to learn the hard way.

Nissan also used M8 Inconel downpipe studs on their turbos (e.g. 300ZX). Part No. 14414-17F00.

http://ep.yimg.com/ca/I/yhst-1534229...2252_459260986

I count 8 threads on the turbine side. 8 x 1.25mm = 10mm engagement. 16 or so threads on the other end plus about 10mm without threads? 40mm overall length? Not quite as long as BEGi's 44mm long Inconel studs but definitely longer than their 37mm long grade 8 studs.

$7.00 each here, but shipping is $14:

1990-1996 Nissan 300zx OEM Turbo to Downpipe Stud

$7.75 each here with $3 shipping:

Nissan OEM 300ZX Turbo to Downpipe Stud Z32 - Nissan performance parts

Awesome explanation, thanks Hornet!

I went out of my way to remove the 2 studs from my exhaust housing before sending my turbo in for the Garrett CHRA exchange, and the guys replaced them (for free, along with all the other hardware) with 2 new studs in the same location. I figured "well, they must know something I don't" so I didn't question it until now.

skou: FM also has a kit of 8mm Inconel manifold-to-turbo studs along with Stage 8 fasteners for $99.95. No length listed though.

Flyin' Miata : Turbochargers : Parts and upgrades : Stage 8 hardware with Inconel studs
https://www.miataturbo.net/attachmen...ine=1362208144

Humm... "10mm master race" is obviously the solution, but I'm not convinced I could drill out my turbine housing or drill/tap my manifold accurately enough. I should go find pricing on those Stage 8 nuts.

Edit: FM sells the Stage 8 8mm nuts for $28.95. Summit is only slightly less at $27.95

$20.04 direct from Stage 8 on Amazon.

Kit 3950 for (4) 8mm-1.25 Nuts.

Stage 8 3950 Turbo Locking Nut Kit with 8mm-1.25 Nuts : Amazon.com : Automotive

Kit 3952 for (4) 10mm-1.50 Nuts.

Stage 8 3952 Turbo Locking Nut Kit with 10mm-1.50 Nuts : Amazon.com : Automotive

Neat! It'd be nice to know the actual lengths on these studs, maybe I'll order a few more for the downpipe and see how they measure up.