Photo of the newly installed muffler.

1978 GMC/MCI Coach bus exhaust conversion

Exhaust conversion on a budget

  • Here at C&S, we service and maintain many different school systems' buses.  We cover 5 different school systems, in three different counties.   Most are public schooling systems, with the exception of one private Catholic school.  Being a private school, servicing and maintaining buses has to be done on a tight budget, so when their 1978 Coach bus needed a muffler, we were ready. It was a 1978 GMC/MCI MC-8 with an 8V71 Detroit motor.  Upon researching mufflers, we discovered that MCI no longer produced the muffler for this coach, and none were available ANYWHERE.  The dimensions and layout of the original muffler were one-of-a-kind, and trying to find any aftermarket outlets to purchase a muffler that would fit in the original's place were all dead ends.  We did however find a company named United Muffler that could build a muffler, to the O.E. specs. What a find this was!!! However, in our lengthy search to find a muffler, we did run across a Nelson Global Products muffler that we thought COULD fit in place of the OEM muffler. While it was different in several variances, it did indeed work! The OEM muffler was a 12"x 23" oval, with a 5" I.D. inlet, and a 4.35" O.D. outlet.   The inlet was clocked at 2, and the outlet was clocked at  7.  The overall body length was 23.5" with an overall length of 27".  The Nelson muffler that we used was 5" I.D. inlet, 5" O.D. outlet, body length of 23.5" and  27" overall length.  The inlet was clocked at 11, and outlet at 3.   The project was finished using the aftermarket Nelson muffler, and we came in well below the cost we had originally projected for the repair.   With a quieter ride and a much less expensive bill than expected, we had one happy customer!!  If you're interested in any of the information above, you can contact us at 308-324-4606, or email us at  


Nelson Global Products part number: 86734M

OEM GMC/MCI part number:  8R-20-35 

You can contact United Muffler at 1-866-229-3402, or visit their website at