Exhaust Manifold: Studs vs. Bolts

[AWeb80]

I'm in the process of building some manifolds for my GP.

I've noticed the 3100 has studs that screw in to the head and then the manifolds and nuts are attached on the back side threads.

I also have extra manifolds from a LX-5 and it just has bolts that attach the manifolds to the heads.

I though it might have something to do w/ the alum heads of the 3100, but the LX-5 is all alum too.


what is the reason to use studs? I'd like to use bolts if I could.

[robertisaar]

because studs are stronger????

that and they're a pain in the ass, a great reason for GM to use them.

but i can see why you'd want bolts (or very short studs) because of how little room there would be to move the manifolds if the studs are preventing it from moving. but there is the upside that you don't have to try to hold the manifold and get a bolt to thread in, as opposed to just slipping it on the studs, threading on a nut and it stays in place

[geoffinbc]

There is no reason. Maybe some assembly line thing. Studs make them easier to install because you can slip on the gasket (if there is one) and then slip on the part and it will stay there while you thread a nut on.

There is also the side benefit of a stud having a more accurate torque reading, plus the ability to measure clamping load with a stretch gauge as well. But on a manifold it is not an issue.

[ForcedFirebird]

I have yet to see a stud break though. A lot of older cars I work on seem to have broken mani bolts even though they were never removed (specially iron heads).

[AWeb80]

i had a couple studs seized pretty good, so i needed to use a vise grip to get them out, thus messing up the threads. where do i get new ones?

[geoffinbc]

GM has them. I got all new bolts for my Trooper build and that was a 90's engine.

[Ray Hamilton]

I use studs. I have some that don't go in more than a quarter inch or so, and stainless nuts. By the way"betterthanyou", I switched to the Lumina 3.1 ECM and it's works great. Thanks for idea.

[geoffinbc]

No worries. I am running it in my Trooper and it works perfect as well.

[WrathOfSocrus]

I went to boltdepot.com and picked up a bunch of bolts that I needed. They had stainless socket set screws which were basically like the stock studs with and internal hex (allen) ends instead of the external hex. Also grabbed a set of stainless lock nuts to go with it.

The shipping was expensive compared to the price of the parts but when it comes to finding anything locally i have had horrible luck since I moved here. I just made a big list of everything I needed and ordered online. I found several things that gave me issues putting together a 3500 such as one of the short LIM bolts was too short to catch the threads on the head and between the end of the threads on the crankshaft being cross threaded plus the crank trigger on the damper, the stock bolt was way too short. In both cases there was room in the bosses to accept a longer bolt. I used a cheap tap and die set and a caliper to determine the threads and lengths required.

If it wasn't such a pain to go across the river and pay $3 or whatever it is now to get in the junkyard, it's probably cheapest to grab a handful of what you need from there. I usually try to talk to several people and make a list so I don't have to drive back and forth any more than necessary.

[OldSkoolGP]

The thing about using bolts is you have to make sure they are the right grade. For exhaust you need Metric 10.9 or 12.8 grade. The problem with 12.8grade though is they usually have allen heads on them, which suck. I'm using bolts because after my header debacle, the fabricator took all my studs and threw them away, and becuase they used such sort bolts, some of my bolts holes got their threads all screwed up, bad for aluminum. If you use bolts, I would recommend going to your local hardware store and getting Class 10.9 Metric M8x30mm bolts. They will catch 10 threads and clamp tight. Then just go 5 poiunds over on your torque spec and you won't have to worry about leaks.

[ghrarhg]

I've found that on the 2.8, they used bolts not studs. The 3400 heads I have are studs, but the studs are too short to mount my gen 2 exhaust manifolds, as the mounting holes are much thicker.

I'll be going with 10.9 hardware, haven't decided on SHCS or HHCS yet though.

[3400-95-Modified]

I use alan head bolts to hold in my headers... Studs wont fit right because of some of the pipe bends.

[PCGUY112887]

I highly suggest using bolts because reusing my studs on my 3500 was a huge PITA due to the pipes being in the way in select places.