GMC Muffler Inlet Size Mismatch

GMC
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INDY400
  • MEMBER
  • 3 POSTS
i got a gmc cab and a half long box my muffler is rusted out i was going to put a purpal horrnie glass pack muffler on it but my problem is the intermediate pipe is 3 inch ond the inlet on the glass pack muffler i was going to put on is 2 and a half inches so if i got a reducer to make the muffler fit well it affect performance.
May 6, 2007 at 1:08 PM
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BURRBRIAN
  • ✓Experienced Mechanic
  • 158 POSTS
You maybe all right with it as the glasspack is a little more free flowing than a stock muffler. Use an adapter to go from 3" to 2 1/2" to get hooked up and the reverse on the other end. Come to think of it, if you don't have any pipe after the muffler you shouldn't have any trouble at all. If the muffler is in the middle of your pipe you should still be OK unless you have a big block like a 454 or the like, then you might find a little restriction, but not asmuch to really bother a stock motor setup. Just my .02$ worth, but unless you allready have the muffler Summit racing carries glasspacks in 3" from 20$ - 30$ or some others that are a little higher. Either way you should be all right. :)
May 7, 2007 at 1:07 PM

Suggested Repair

Use a 3-inch to 2.5-inch adapter to fit the glasspack, and a reverse adapter on the outlet if pipe continues past the muffler. The freer-flowing glasspack should cause only minor restriction on a stock engine, though a big-block such as a 454 may notice it slightly. A 3-inch glasspack is another option if the muffler has not already been purchased.

Conversation Summary

The owner of a GMC cab-and-a-half long-box truck has a rusted muffler and wants to install a Purple Hornie glasspack. The intermediate pipe is 3 inches and the muffler inlet is 2.5 inches, so they asked whether a reducer would hurt performance. The expert said an adapter should be fine because a glasspack flows more freely than a stock muffler, with little concern unless the engine is a large big-block, and noted that 3-inch glasspacks are available.

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