[Richard Hudgins]

GN,

Let me try to answer to the best of my limited knowledge.

1. The negative pulses are a result of rapid pressure change (read expansion) from the primary into the secondary. Every time that a positive pulse (High pressure) meets a expansion point, a negative is created. Therefore, when the pulse reaches the collector a negative pulse is generated. However, there is still considerable pressure and therein energy in the initial positive pulse. When this continuing pulse reaches the sidepipe (which typically has a greater area than the collector) another negative pulse is created. This positive pulse will still have considerable energy after this event and will produce another negative pulse at the exit point to atmosphere.

The timing of these pulses are very critical to cylinder scavenging and tuning as I am sure you know. We used to go to a lot of trouble with anti-reversion schemes etc. to place the negative pulse X distance prior to the exhaust valve face to maximize the resulting positive pulse and to minimize mixture dilution due to the creation of this positive pulse.

2. You are correct. There are standard equations for determining the correct primary and secondary lengths for the exhaust system. A typical one used for our type of engines (Low rpm, large bore) is swept area X 2 = primary pipe volume. Or for a 351 43.875 X 2 = 87.75 Therein, with a 1.75 primary the total length should be 36.5625 to the collector. (note: this needs to include the port area as well) This volume will give you good results in the 4>6000 range. (Of course, now you have to factor in the collector and sidepipe volumes to match pulse timing.)

3. Yes, temp changes mach number. Also, the higher the temp the higher the energy contained in the positive pulse. Therein, the strenght of the negative pulse is greater. Each time there is a expansion in the system, the energy of the pulse is reduced from cooling. Therefore, the higher the specific heat at each expansion event the stronger the pulses. I have seen very positive results with ceramic coatings as it pertains to power production.

4. The design of the sidepipes on these cars is basically good. But, they are seldom sized to the engines installed due to the wide variety of engine choice and visual contraints.

Now, we need someone who really knows exhaust design to give us good information.