Exhaust studs 1991 Trooper LS, 2.8 v6

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Exhaust studs 1991 Trooper LS, 2.8 v6

Postby staggerlee » Sun May 09, 2021 11:55 am

Does anyone know the proper stud size/ thread pitch /length for the studs that attach the exhaust manifold to the exhaust pipe?
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Re: Exhaust studs 1991 Trooper LS, 2.8 v6

Postby Ed Mc. » Mon May 10, 2021 2:49 am

What you're looking for is commonly known as a "Bolt/Spring".

I couldn't find a listing for Isuzu 2.8 but there are a bunch of GM rigs with the 2.8 V6, including the S10 PU and Blazer, that use this set:

https://www.rockauto.com/en/moreinfo.ph ... &jsn=10717

AP Emissions 4970. You might be able to find these at the auto parts store, or eBay, and see if they compare to what you need.

S10 TBI 2.8's use the same exhaust manifolds as the ZuZu version, so there's no question that these studs will screw into your 2.8's manifolds.

https://www.ebay.com/sch/i.html?_from=R ... 5337131047

Summit Racing carries it too:

https://www.summitracing.com/parts/aph-4970

HTH.........ed

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'90 3.4 Troop LS;
'89 Troop RS (Exhaust Valve Challenged), now gone to a Good Home!
Yes, I am a Trooper-Holic!!!
Keep On Troopin' !
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Re: Exhaust studs 1991 Trooper LS, 2.8 v6

Postby staggerlee » Mon May 10, 2021 8:43 am

Thanks, but the bolt spring is the opposite end of the section I'm looking for the studs for. Some of the s-10 manifolds are sold with the spring, so my guess is the Trooper 's short length of pipe between the manifold and part # 93982 is not included in the s-10? I also noticed that 4970 shows up for the 1990, but not the 1991 s-10, so maybe the trooper is a model year behind. I might have to pull the driver side's out to get the size, but trying to remove is how I broke the passenger side in the first place.
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Re: Exhaust studs 1991 Trooper LS, 2.8 v6

Postby Ed Mc. » Mon May 10, 2021 2:26 pm

staggerlee wrote:Thanks, but the bolt spring is the opposite end of the section I'm looking for the studs for. Some of the s-10 manifolds are sold with the spring, so my guess is the Trooper 's short length of pipe between the manifold and part # 93982 is not included in the s-10? I also noticed that 4970 shows up for the 1990, but not the 1991 s-10, so maybe the trooper is a model year behind. I might have to pull the driver side's out to get the size, but trying to remove is how I broke the passenger side in the first place.


I found a diagram I saved of the manual-trans Trooper exhaust system:

V6 Exhaust_Manual_'89-'91.jpg


It shows everything up to the exhaust manifolds, excluding the bolt/spring assemblies. IIRC, all or most of the flanged connections downstream of the exhaust manifolds use thru-bolts and they're probably 8mm (or possibly 10mm). There may be some flanges with a captivated nut. But it's been a while since I've had mine apart. The S10 exhaust is definitely simpler than what they cobbled-up to stuff the GM engine into a Trooper.

BTW the exhaust "wye" is terribly restrictive, it necks down to less than 1/78" and is a huge bottleneck to the system. I plumbed in a dual-inlet cat with 2-1/2" single outlet. Went with 2-1/2" tailpipe along with a Dynomax Super-Turbo muffler. The stock downpipes are 2" so with a bit of fabrication, you're able to run them right into the cat. The cat has an O2 sensor bung, so the O2 sensor warms up quicker and runs warmer. Works great and it really "uncorked" the 3.4. A 2.8 couldn't use more than 2-1/4" tailpipe without losing a ton of low-end torque, though.

FYI, for stuck/rusted parts, a 50/50 mix of acetone and ATF has been proven to be more effective than commercial penetrants like Kroil and PB Blaster, among others. Just watch out for the volatility, acetone is quite flammable. You might soak a joint in the mixture for several days and see if that helps.
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'90 3.4 Troop LS;
'89 Troop RS (Exhaust Valve Challenged), now gone to a Good Home!
Yes, I am a Trooper-Holic!!!
Keep On Troopin' !
Ed Mc.
I am the Stig
 
Posts: 4243
Joined: Thu Aug 14, 2003 1:26 am
Location: Poulsbo, WA
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