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Old 07-31-2020, 03:20 AM   #1
Cristiann8
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Exhaust trailing arm hole question

Is a 3 inch hole to drill into the trailing arm crossmember for 2 1/2 inch exhaust enough? I bought a 3 inch hole saw but it looks quite small but I want to make sure before I start drilling my crossmember.
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Old 07-31-2020, 09:07 AM   #2
SIXTY9
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Re: Exhaust trailing arm hole question

I used a 4" hole saw on mine just to make sure it had enough clearance. I did add a 1/4 plate to make it stiff.
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Old 07-31-2020, 09:17 AM   #3
Grumpy old man
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Re: Exhaust trailing arm hole question

That's tight , I used 4" for 2 1/2" pipes and it was a lot easier to mark the hole location and use a cut off wheel to cut thru the cross member and get a tight fit on a short section of pipe to weld in to place , The 4" pipe came from Metal supermarkets and they cut and shipped it to me for less $ than I could have driven there to get it across town .
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Old 07-31-2020, 12:29 PM   #4
SCOTI
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Re: Exhaust trailing arm hole question

They also have bolt-in kits out there for simplicity if that helps....

https://azproperformance.com/collect...outs-63-72-c10
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Old 07-31-2020, 04:57 PM   #5
LS short box
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Re: Exhaust trailing arm hole question

I cut mine with a 3.5" hole saw and reinforced with a flat plate of steel 3/16" with a 3.5" hole cut in it.
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Old 07-31-2020, 05:23 PM   #6
70STOVEBOLT
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Re: Exhaust trailing arm hole question

I used a 3 1/2 hole saw on mine. Unless you are going to have 500+ HP you don’t need to reinforce it.
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Old 08-01-2020, 12:47 AM   #7
gmc684x4
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Re: Exhaust trailing arm hole question

I would say re enforce the hole for a professional fit and finish
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Old 08-01-2020, 04:51 PM   #8
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Re: Exhaust trailing arm hole question

My frame was bare when I cut the holes for the exhaust so it was easy to do. I didn't know what kind of strength I removed when I made the hole so the reinforcement plate seemed like a good idea and I kind of like to do fab stuff. My LS1 did 380 rwhp on the chassis dyno so about 450 at the crank?
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