1G Cracked exhaust manifold and broken studs

Red Rider · Jun 30, 2021

Background: 1990 GST, 150,000 miles, I owned it from 90,000 to 150,000, stock engine, no overhaul I'm aware of. I'm taking off the head to repair from a snapped (new) timing belt. First thing I see is the lower furthest driver side exhaust manifold stud is sheared off. Huh. 3 more shear on removal, the center and 2 on the left. Get the head up, past the single stud on the turbo, slide off the manifold and It was clearly leaking badly from the passenger side, and less so on the drivers side.

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Turn it over, and I find this:

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Is this a repairable crack? Is it better to just replace it? I haven't put a straight edge on it yet, but if it's warped I'd guess it's trash.

With no oil consumption, good power, I'm thinking not to do an entire overhaul since I'll drive it like 4,000 miles a year. And workshop time is not unlimited.

What is a recommended manifold for a stock turbo? What is the cracking history on aftermarket manifolds? Performance wise the farthest I think I'll ever go is 550 injectors, stock turbo, upgraded air filter and larger exhaust, shooting for the high 200s or 300 hp tops. The turbo seems ok, no shaft play.

Stapl3 · Jun 30, 2021

You'd be hard pressed to find a stock 1g manifold that isn't cracked. Seek out a 2g manifold. They flow more also. If you're feeling DSM-rich, go for the FP cast.

You could weld that, but welding these cast manifolds takes someone that knows what they're doing. It's not worth the effort.

Red Rider · Jun 30, 2021

Stapl3 said:
You could weld that, but welding these cast manifolds takes someone that knows what they're doing. It's not worth the effort.

Luckily, I'm near Aircraft Welding in Hartford, they are welding magicians, but not cheap. The new FP is $275 unported. There's $110 stainless manifolds on Ebay, although lots of threads I've read aren't enthusiastic about Ebay Chinese parts. There's a new Dorman manifold ceramic coated on Ebay by the PA coating company for $180. There's an OEM 2G manifold on Ebay, but at $120 and possible machining to make it really flat, I'm sketpical.

Given my modest under 300hp goals, does anyone have experience with Dorman vs FP? Is porting the FP necessary? Anyone had luck with Ebay stainless manifolds?

pauleyman · Jun 30, 2021

New oem manifolds are 300$. 2g is better. It's not a 100% bolt on. Needs minor grinding on one corner. No big deal. Later manifolds also have larger studs on the ends. Yiu don't have to change them but if head is being machined now would be the time. Replace all the studs, not just the broken ones.

NOSLO2PT0 · Jun 30, 2021

The 2g manifold is perfect for what you need. I’m sure you can easily find someone that has one laying in their parts bin that would sell it for cheap

Sniffbooger · Jun 30, 2021

I have a 2g exhaust manifold in my storage....I also have a stainless eBay tubular header on my car, been on there for many years...seems to work fine with my 16g turbo...however, I also have a couple exhaust studs broken and stripped...might have something to do with stainless headers expanding/shrinking too much...

Mech Addict · Jul 1, 2021

I’ve had my 1990 gsx manifold off, and never noticed any cracks, just fyi. If it did, I would swap to a 2g. I replaced the studs and nuts, though the very last one I final torqued (pass-side end) kept tuning before reaching full spec. Have to fix that sometime in the future, but just watching for now. I had 3 broken before I put in the new, but got them all out myself with a little propane and some liquid wrench and a stud extractor. Yours look more tricky, and sounds like you’ll have the head off anyway, so that allows more options to fix.

Jk's97DSM · Jul 1, 2021

Just do it once and do it right.
FP manifold
Replace all of the studs and nuts with quality parts
Red Loctite the studs into the head
Don’t put loctite on the nuts but tighten evenly from the center out.
You shouldn’t have an issue if it’s done right.

Sniffbooger · Jul 1, 2021

That post was worthy of a screenshot!! But those FP manifolds are NOT cheap....

Bird58 · Jul 1, 2021

Jk's97DSM said:
Just do it once and do it right.
FP manifold
Replace all of the studs and nuts with quality parts
Red Loctite the studs into the head
Don’t put loctite on the nuts but tighten evenly from the center out.
You shouldn’t have an issue if it’s done right.

agreed but if your in a punch you can find a 2g mani for cheap.. just sold mine for $40

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1G Cracked exhaust manifold and broken studs

Red Rider

Stapl3

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NOSLO2PT0

Sniffbooger

Mech Addict

Jk's97DSM

Sniffbooger

Bird58

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