I'd like to know the answers to those questions too! Describe how the car ran after the exhaust change with some indication of a measured power loss, and give an explanation why you think the exhaust caused a power loss. I'm a fact-based person!
What did Pontiac claim would happen if the ratio strayed very far from 70%? What were the flow numbers of the heads in question, and what do they say now about the "ideal" ratio?
The idea is to get the bad air out and the good air in. By using negative pressure in the exhaust system (not to be confused with back pressure) more power is made. Tried, tested, proven, repeatable, transferable to all street engines regardless of make and port flow ratio. Yes, you can have less back pressure than open headers by tuning the exhaust system with the right size and length of pipes.
Claus, I would attribute the 10 hp loss shown in one of the dyno tests from using a particular muffler to a change in effective length of the pipes that the engine "sees", but they don't describe the different mufflers so I don't know for sure. The above article explains what happens with different muffler types.
I've worked full time building race cars and hot street cars for most of the last twenty years so the number of cars that I've worked on is likely well into the hundreds. I have yet to witness a single car that didn't respond to a better flowing exhaust system and have yet to see one that liked a more restrictive exhaust - including Pontiacs! Of course, I haven't seen everything yet either! And I'm always willing to learn!
