ExhaustNotes

Pipes From One End to the Other

By Ron Ceridono

It's been said that no act of stupidity goes unpunished. Not long ago we had the opportunity to scientifically test that very theory by virtually destroying an entire exhaust system on our project SpeedRodder and found it to be absolutely true. But, in our defense, it wasn't one stupid act, it was three.

Our problems began with a small exhaust leak that developed in one of the headers on the '32. We were on the road, in the middle of nowhere, when the slight telltale exhaust leak caught our attention. A roadside examination revealed that a tiny hole had developed where one of the pipes joined the collector. It appeared an over-zealous polisher at the chrome shop leaned a little to hard on a weld (let's call this Act 1) and as a result a pin-sized hole developed; fortunately it was on the bottom of the pipe and could easily be repaired and remain unseen, so we thought.

Continuing on our merry way to the next little dot on the map, we stopped at a repair/muffler shop and asked if we could borrow/rent a welding outfit. "No" was the response, but their "best man" could fix our problem, no sweat. Unfortunately, their best man wasn't all that good and by the time we stopped him the pinhole had grown dramatically (Act 2). Now we were stuck; the header had a huge gash that had to be mended (here comes Act 3).

At this point the ace welder decided he was in over his head and offered to loan us the shop's torch (presumably so we could be blamed for his mess). To help close the gap and make welding easier, we loosened all the exhaust hangers. That did in fact make welding easier, of course by now the chrome was cooked and the weld ran almost all the way around the collector, but the worst was yet to come. In our haste to get on the road, we forgot to tighten the hangers. As a result of the entire exhaust system hanging loose, the strain on the headers caused several more cracks, and two out of the three hangers tore loose from the pipes, taking chunks of tubing with them. Our testing was completed, we had successfully destroyed a perfectly good exhaust system and stupidity had indeed prevailed.

Building The New Headers

Faced with fixing what we had or beginning again from scratch, we opted for the latter. We liked the looks of the original headers, and we wanted the same style: gracefully flowing primary pipes joining a long tapered cone. By sheer luck we happened to meet just the guy to build them, Rick Carlyle of SoCal Engineering. Rick's a genuine craftsman and has been building headers since he was a kid, but he's still a well-known secret. Rick has always flown under the radar and doesn't advertise much because he has more than enough business to keep him busy just from word of mouth. So, those who wanted the best simply had to search him out. We got lucky and met him by accident.

When we showed Rick what we had, and explained what we wanted, he agreed to build a new set of headers; coercing him to let us follow him around and take photos was slightly more difficult. However, thanks to warmth, charm, and the perception that we wouldn't go away until he gave in, he ultimately welcomed us with open arms.

What sets Rick's headers apart from most others, and the thing that most rodders notice first, is the way he connects the individual pipes to the tapered cone. Rather than joining them at an abrupt 90-degree angle, Rick goes to great pains to blend them with curved primary pipes. The result is a cleaner appearance and arguably better exhaust flow. To maintain an uncluttered appearance, Rick joined the pipe leading to the mufflers directly to the collector without a flange. The three-bolt connection to those pipes is hidden under the car. And while that additional pipe hanging down makes the headers more cumbersome to install, the look is much cleaner. Stepping Up To Stainless

Although we could have repaired the remainder of the exhaust system once the headers were replaced, we opted to install a new stainless steel system. There were several reasons for the change, not the least of which are that stainless will last virtually forever, it looks great when polished, not to mention this approach would also give us the opportunity to try a pair of stainless MagnaFlow Wide Open performance mufflers.

When it comes to mufflers, there are basically two choices: straight through or some sort of reversion (chambered or reverse flow) design. While the manufacturers of each type are prone to tout the virtues of their product, according to Mike Jones of MagnaFlow, the key to performance is eliminating excessive backpressure while maintaining exhaust gas velocity. To that end, MagnaFlow mufflers are of the straight-through design, which they feel is the best.

As with reverse flow/chambered mufflers, the design of the straight-through style varies, although there are some basic similarities. All have a perforated pipe wrapped with some sort of sound absorbing material. At one time, fiberglass was used as was packing that looked like coarse steel wool (hence the names glasspacks and steelpacks). The type of the tubes also differs; some used holes while others have small louvers. While the louvered cores were common, many of the cheap mufflers on the market had cores that were cut with gang saws and the resulting ragged edges on the inside of the tubes impeded flow, and when the last of the fiberglass blew out the tailpipes they became noisy to boot. But that was then, this is now.

Today's straight-through mufflers, as exemplified by MagnaFlow's offerings, are light-years ahead of the old glasspack. First and foremost, they offer reduced backpressure. Simply put, backpressure in an exhaust system is like putting your thumb over the end of a garden hose; more pressure applied to the end of the hose results in less flow. So, if an engine's exhaust flow is reduced by excessive backpressure, the cylinders aren't emptied as completely on the exhaust stroke, they can't fill as well on the intake stroke, and the result is less power. By using a core with holes, as opposed to louvers, exhaust gas flowing through a MagnaFlow muffler encounters less restriction, and it's much less turbulent, which also aids flow.

While maintaining maximum exhaust flow as a result of minimal backpressure is important, a muffler must also keep the exhaust reasonably quiet. While OEM applications generally call for whisper-like sound level, performance enthusiasts want their car's exhaust system to have just the right sound. In that area, straight-through mufflers have the others beat, and that brings up another difference in basic design. With straight-through mufflers, sound levels are a result of the core size and length. The smaller the core and the longer the muffler, the quieter it is and tailpipe length is irrelevant. On the other hand, the sound level of reversion mufflers can be altered significantly by changing the length of the tailpipes.

Pipes

Exhaust pipe sizes are a subject unto themselves, but here are a few general guidelines from a man who knows. Although many subscribe to the "huge is best" theory of pipe selection, Jones points out that bigger is not necessarily better, and this is coming from a man with an impressive engineering and manufacturing background. Jones advises that while pipes that are too small can increase backpressure, they must not be so large that gas velocity drops off. Fast moving gasses help evacuate the cylinders, which is often referred to as the scavenging effect. And while larger pipes may reduce backpressure (the industry standard is 2.8 lbs with 1.8 to 2.2 lbs believed to be the optimum), Jones points out that oversize pipes will result in lower exhaust gas velocity, which reduces the scavenging effect, which reduces low-end torque.

So what size pipes should you run? That depends on a host of factors, but as a very general rule they should be 2-1/4 inch minimum. To further generalize, small-block Chevys respond well to 2-1/2-inch pipes, while small-block Fords can actually benefit from slightly smaller pipes (1/8- to 1/4-inch smaller) to maintain exhaust gas velocity for better bottom-end performance. On the other hand, Jones points out that Mopars can benefit from going larger, in most applications 2-3-inch tubing works best. Again, keep in mind, these are ballpark numbers and adding major modifications to the mix, such as blowers, nitrous, and the like, can change the engine's requirements dramatically.

One final note about pipes. If at all possible, use mandrel bends as opposed to the more common muffler shop "crush" bends. Mandrel bends are made by drawing a die, or mandrel, through the inside of the pipe so the diameter remains constant. By comparison, tubing benders crush the pipe slightly as dies bend it from the outside only. This process reduces its cross section, and as a result, flow is reduced. As an example a 2-inch pipe has a flow area of 3.14 square-inches., while a pipe shaped on a conventional bender will have that area reduced to approximately 2.50 square-inches. There's not much sense in building a killer exhaust system with big pipes only to choke it down with restrictive bends.

Hangers

Perhaps the most overlooked items on an exhaust system are the hanger, but given what they have to cope with, that can be a major mistake. Hangers must be able to withstand the engine's movement while keeping the pipes from coming in contact with the various and sundry items have to snake their way around. In addition, an exhaust system can grow by as much as an inch in length as the system heats up, so the hangers must be able to allow for that. And of course, hangers must isolate the passenger compartment from noise and vibration. To address all those concerns, we used MagnaFlow stainless and rubber hangers.

Sounding Off

A real hot rod has a long list of identifying characteristics. Certainly one of them is how it sounds, and we've never had one that sounded better. The MagnaFlow mufflers sing in a deep, baritone that is truly music to the ears. And although we weren't able to make before and after dyno comparisons, the seat of our pants tells us that performance has also been improved. No exhaust leaks, a great sound, improved performance, and no stupid mistakes!