Fred Cal from Batavia, Illinois, recently submitted a great list of subjects for possible discussion. Several of those will be covered in this column.

How about those claims for increased airflow through the newer performance mufflers? Does airflow relate directly to performance? As with all factory components, the stock mufflers and pipes were a compromise, with noise, cost, warranty, and space limitations all being considered. The stock type mufflers did cause some back-pressure, which adversely affected performance. The pipe configurations andlor size also caused back-pressure in many applications.

The aftermarket has applied a great deal of research on exhaust components and problems, and have developed amazingly good products. Most “performance” mufflers provide some degree of quieting, all provide improved airflow, and many look good enough to display to bystanders! However, in order to obtain or maintain a reasonable market share, some makers make claims of “increased airflow”, “flows better than a straight pipe”, or “10% better flow than competitor X”. We have conducted extensive testing of mufflers on actual strip performance and found that with a single 2-1/2″ muffler on a 12.50 vehicle, there is very little performance difference between all brands of performance mufflers. When tested with a good dual system with some type of crossover, there is almost no measurable difference between brands, providing similar sizes are compared. Static airflow will be affected by test pressure and the methods in which air is directed into and out of the muffler. Accordingly we feel that bench tested airflow on mufflers is misleading and should carry very little weight when evaluating muffler performance.

There are distinct differences in pricing, noise levels, build quality, and packaging of “performance” mufflers. Here are some general observations about mufflers:

1. The larger the volume in a muffler case, the quieter the muffler.
2. Exhaust noise is the result of two factors – the noise escaping out the tailpipes, and the noise generated by the muffler case. Round or oval mufflers produce very little case noise because there are no flat sides (other than the ends which are typically reinforced), and thus no areas to vibrate in harmony with the exhaust noise passing within the muffler. Any vibration of a flat surface will generate noise. Rectangular mufflers can generate noise which will be heard inside the car as a resonance. The use of heavy metal cases, extensive welding of the flat metal to internal components, and internal insulation can help reduce the noise produced by the case in this style of muffler.
3. The use of stainless steel will increase the expected life, add to the cost, and produce a better looking muffler.
4. Larger pass tubes, or larger passageways within the muffler case will always make the exhaust noisier, and may reduce back-pressure.

Excessive noise is not an indication of improved performance, and reasonably quiet mufflers are not necessarily restrictive.

To summarize, when a muffler of a given pass-through size produces reasonable flow capability, slight additional flow capability probably will not be recognized by our street/strip vehicles. When shopping for a performance muffler, determine how much noise and/or tone you want, how long you expect the muffler to last, the package size you can use, whether appearance is of significant value, and finally how much money you want to spend. We feel that the average street or street/strip vehicle will not be able to measure any performance differences between the top 8 or 10 mufflers available if similar sizes are used on a good dual system.

Uniform diameter head-pipes of adequate size will improve performance over carelessly bent or badly crimped pipes. Mandrel bent pipes provide the best available performance. Tailpipes are not as critical of irregularities in construction due to the cooling of the exhaust and resulting lower gas volume. However, severe crimps or wrinkles should be avoided, and mandrel bent pipes should be used when practical and possible.

Fred also asked if we have conducted any drag strip testing of synthetic lubricants. We have not, although we use synthetic oil in our engines after the break-in period. One of the most respected engine builders of all time, Smokey Yunick, states that synthetic oil is superior in all areas of lubrication. Smokey has his favorite brand, but we feel that all major brands of straight synthetic will provide superior lubrication. We do feel that many owners use heavier weight oil (both conventional and synthetic) than is necessary. For example, 50 wt. or 20-50 racing oil is necessary for racing engines that have bearing and operating clearances set for that weight of oil, but our factory style engines do not need such heavy oil. Extremely heavy oil, and/or very high pressure oil pressures add excessive load on the oil pump, which causes accelerated wear on the distributor drive gear, and costs valuable horsepower to the engine. When we consider how much the quality of all major brands of oil have improved since our Pontiac V8 engines were produced, we could probably safely use even lighter weights of oil than originally recommended by the factory.

Synthetic lubricants are available for transmission (auto and manual), and for rear axle assemblies. They may provide some advantages in lubrication, but at a very expensive price. We are a bit wary of the effect on the operation of friction components, such as the clutches in auto transmissions and limited slip differentials, so have not tried them. We also doubt that measurable differences in performance would be found with our relatively heavy vehicles.

We have noted the advertising of some probable fact and then inferring that improved performance will result. In the case of the synthetic wheel bearing grease, the drag caused by properly adjusted and lubricated wheel bearings on a 4000# vehicle is such a minuscule amount, an improvement of 100% of the drag would still be un-measurable. In fact, the bearings could probably be run without any grease, and the vehicle would run about the same until the bearing seized. When evaluating such advertising, consider the power producing or power consuming effect of any engine or running gear component or material. If it is responsible for a relatively minor proportion of the total power output, even significant percentage improvements of that item would still be almost undetectable! For example, a flexible fan blade is advertised as increasing power because the blades bend under high RPM. The advertising does not tell you that it requires power to bend the blades and keep them bent. In actual tests, the factory 7 blade thermo-clutch fan assembly allows improved drag strip performance and superior cooling in normal driving when compared to any other type of fan. The aftermarket provides many quality parts/components, but evaluate them carefully and thoroughly before investing your money for expected performance gains.

Thanks to Fred Cal for his input, and we will discuss more of his suggestions later.