I´ve been doing a lot of research/thinking about the oem exhaust system on a US 328 and the replacement of oem components... One thing I have been wondering - is the oem muffler a Ferrari-only item or is it used on any other vehicle? The reason I´m wondering about that depends on whether Ferrari designed the system based on the engine characteristics OR they just used a muffler to fit the car. If they actually designed the system and had a muffler supplier build a muffler to fit the engine characteristics, then replacing the muffler with anything OTHER than a muffler with the same internal volume will reduce the oem performance. A louder muffler means nothing performance wise - the only thing that matters is the volume as related to the tuning of the exhaust system and its effect on cylinder filling. As an example - a HEAVY oem muffler of X volume will be quieter than a LIGHT aftermarket muffler of X volume though there will be no difference in power. The heavy muffler will absorb sound in the same way that a cast iron waste pipe in a house is quieter than the same diameter plastic pipe. Certainly, lighter is better from a power to weight point of view but other than that, there is no advantage to a lighter muffler from a HP point of view. A muffler with LESS than oem volume woulld (assuming again that Ferrari tuned the system for best power) raise the peak power RPM above the oem and very likely would put the optimum power peak too hgh in the rev range to be useful. Exhaust (and intake) tuning is often used to optimize power over a broader range than what might initially be expected. Modern engines have adjustable cam timing, adjustable intake volume, and adjustable exhaust volume. But cars like the 328 did not have that available at the time. So engines had compromises built in to provide smooth power across the rev range at the expesnse of max HP. For example, the exhuast could be tuned for max power at say 7000 RPM while the intake was tuned for 6000 RPM, giving a better OVERALL usable power curve. Additionally, exhaust headers can be tuned to vary the power output from each cylinder over a range depending on individual header length. That is, by varying the length of each header tube, the max power output of each cylinder could occur at a different RPM. This again would ensure a broad overall power curve at the expense of max power. I do not know if Ferrari designed the engines in this manner or not but if they did, any change in the exhaust system - mufflers, cat converters, etc, to items with a DIFFERENT internal volume would change the oem-designed power output. Looking at pics, it appears to me that some aftermarket mufflers are essentially copies of the oem as far as volume is concerned. These mufflers would duplicate oem engine characteristics. Mufflers that do NOT copy oem muffs would likely loose power in the oem RPM range, again IF FERRARI tuned these systems. The noise level of muffs has no effect on the power level; the internal volume is the issue. Virtually any available muffler can flow enough air to support the HP level of these engines at least up to the 500HP level. But will the VOLUME of the muffler provide the proper tuning? There are tons of examples where straight pipes reduced the HP on an engine within the useful RPM range because the exhaust tuning was disrupted. Whether this will occur or not depends on whether the factory TUNED the entire system in the first place or whether they just stuck a muffler on there that fit in the chasis. Anybody know what the factory did with these cars?
