Unitized or Multi-Piece Exhaust Systems?; From the converter to the muffler assembly; Coming up the rear

Text and images by Jim Anderton

“Import-type”, “all-welded” and “unitized” are common terms for modern single-piece exhaust components and all promise fast installation and OEM levels of fit, noise suppression and back pressure. Exhaust work is a low-margin service for many service businesses, requiring minimal installation times to maintain profitability. Are single piece units easier to install? SSGM Editor Jim Anderton went gun-in-hand and installed single and multi-piece systems back-to-back on identical Honda Civics to shake out the quick and the dirty.

1. Why we’re here. This Honda Civic system has seen it’s service life “stretched’ by some typical do-it-yourself repairs. Silicone seal plugged a serious exhaust leak (but not for long), a perforated bracket is welded to the exhaust pipe, and the whole assembly is wired to the chassis.

2. Another exhaust leak, this time at the front to rear flange. This time it’s a gasket failure. By upselling to the whole cat-back system, you can ignore this problem and seat the new gasket into clean, straight flanges.

3. By welding the broken system at home, this customer locked the pipes into a bent configuration that guaranteed contact with the floor pan. Fortunately there wasn’t a brake or fuel line nearby.

4. The home-made muffler strap is there for a good reason. Honda’s mounting system suspends the muffler from offset hangars, allowing the assembly to rotate when it weakens with age and rust. The result is a tailpipe that pivots up into the rear bumper, rather than down. Many consumers won’t notice the effect until the system fails completely.

5. Getting the fire welded steel gasket out of the machined groove in the flange is surprisingly tough. Its essential to get all the debris out of this critical joint to make sure the new gasket fits flush all the way around. The heat here is severe and will burn through if the gasket doesn’t compress evenly.

6. Another exhaust leak, this time at the cat’s rear flange. The indentation in the gasket was the start of something bigger.

7. Now that we’re here, why not look at the catalyst bed? Shine light into the end and look for plugging, fouling or broken or loose ceramic substrate.

8. The same reasoning applies up front. If this joint fails after you install a new cat-back system, the customer will perceive it as a quality problem with your workmanship.

9. Amateur repairs at the rear of the system can have consequences up front. Note how the right rubber is stretched much more than the left. Both are oil soaked with undercoating and oil-pan gasket seepage, shortening their lives. The stressed one is especially vulnerable.

10. After a thorough cleaning, bending the removed right hand rubber shows a tear amongst lots of microscopic cracking and weather checking. In its relaxed state, it looks fine.

11. Another casualty. This rubber is deteriorated, helped to an early death by its strained, twisted mounting. The hangar showed evidence of torch work on the old “white box” assembly. Heating hangars to get a better alignment for the rubbers is a last resort. Good parts should fit up to the OEM locations.

From the converter to the muffler assembly

12. New rubbers are essential for a quality job. The front pipe on this Civic (looking forward) uses rubbers of a different design to the rears, and unlike the rears, they’re canted inward. This keeps the resonator centred in the very small floorpan tunnel. If one is vertical and the other is stretched at a severe angle, check the fit. If the pipe is correct and the mountings are still not symmetrical, bend hangars as necessary. This ArvinMeritor pipe fitted properly out of the box.

13. The front pipes are similar. Note the difference in the ArvinMeritor IPS pipe on the left and the “white box” piece, right. The premium unit has integral heat shields, and OE-type hangars that allow the mounting rubbers to slip on in the direction of the pipe’s fit-up to the converter.

14. This body-mounted heat shield is O.K., but for how long? Take a moment with the pipes off to look and feel around for loose or distorted shielding.

15. The multi-piece rear system on the right (ArvinMeritor Original Equipment Replacement) uses six parts, compared to the two (gasket included) for the single piece on the left. (ArvinMeritor Import Professional Services) Will both fit well?

16. At the rear suspension kickup, the system’s welded hangar is exactly parallel to the chassis mounting, allowing the rubber to support the weight without twisting. Note the line of body-colour red showing through the worn undercoating. It’s caused by contact with the old broken pipe. Touching up the undercoating is a quick, value-added service that should be noted on the work order. The rear strut is also showing signs of oil leakage.

17. A closeup of the mounting rubber shows the correct straight up and down position. Twisted mounting strains the rubber, while staggered or offset hangars stretches the rubber at rest. OE systems stretch the rubber only to accommodate movement in the system, without significant preload.

18. You’ve just done DaVinci-quality work on the system, and you leave a dull gray pipe sticking out the back? Sell a nice chrome tip to complete the job. It’s the only part of the system the customer regularly sees, and it adds a perception of quality.

19. If you’re installing a multi-piece, this arrow is very important. In this Honda application, the muffler won’t go on the wrong way around, but in many it can. Arrows or markings like “In” and “Out’ are not just recommendations. The muffler will not flow properly if the gases go backwards.

20. This Honda uses a transversely mounted muffler requiring the exhaust gases to make two right turns to exit the body on the left side. Welded systems should be level both front to back and left to right to maintain proper clearance with the floorpan at all times. If it’s necessary to bend the hangar to level the unit in one direction, check to make sure it’s still level in the other.

21. Quality all-welded systems have a clean appearance, and clear critical areas like the floor pan’s spare tire well. Even incidental contact here can generate noise-related comebacks.

22. Another reason to use first line parts. Suspect that there’s something wrong with the pipe? Can’t get a good fit? The “800” number gives technical advise, and almost as importantly, lets you check that you have the correct part number for you application. Do jobbers occasionally ship the wrong stuff? You bet.

23. If there’s a silver lining in performing exhaust work, it’s the ability to get underneath the car and look around. Coolant on the CV joint, cracking in the joint boots are worth investigating, and the oil pan plug and oil filter are simply staring at you. So what if it’s 500 kilometers before the next scheduled change, you’re right there! Suggest needed service as soon as you can, preferably while the vehicle is in the air.

So that’s the difference between a welded and a multi-piece system? For the Maremont pipes SSGM installed, the answer is mainly time. Both mounted to original equipment standards and bolted up straight and level. The extra time for the multi-piece system was devoted to alignment and torquing the clamps. For SSGM’s admittedly rusty editor, Jim Anderton, the difference in installation time was approximately 15 minutes, including chasing the clamp nuts all over the shop floor.

Both perform well, and there’s nothing to choose from the consumer’s point of view. From my perspective, on this Honda I’d choose the welded system for its convenience, but more importantly for its “just like the factory” sales appeal. If you can’t source a one-piece system easily, a properly installed multi-piece from a reputable manufacturer will work fine too. It’s literally the dealer’s choice.