Exhaust choices - importance of back pressure on a CIS car?

[twobone]

Yes, I know the debates on exhaust upgrades are endless.

On a more scientific slant:

My mechanic had a good chuckle last night.

He told me a year ago that the Bursch I bought to go with my SSIs was a peice of cr*p. Well a year later, I was aking him if he had any good used exhausts to replace mine.

In his mind (and mine) the sound is too obnoxious.

Also, he says that CIS cars need exhaust back pressure to work effectively. That is one reason why SSIs are the key factor in the power improvements and that the exhaust is less imortant, specifically for CIS cars.

So, given that CIS seems to be a bit of a black art, is there some vailidity to going back to a more stock type exhaust?

[javadog]

More back pressure is not what you are after. The reason the SSI heat exchangers work better than what came on the car has to do with the diameter and length of the primary pipes, mainly. Exhaust pipes work in conjunction with valve timing and other variables to affect the torque curve of the engine. What is optimum at one point in the torque curve will not be optimum at other points. It's a long story and I type slowly.

Exhaust pipes used to be a bit of a black art (especially those for two-stroke engines) but now there is a fair bit of knowledge out there. Buy a book on exhaust and intake systems and you'll learn a lot.

If you want a reasonably quiet new muffler, I'd suggest a 2-in, 1-out Monty.

JR

[Dantilla]

Engines don't need back pressure, they need velocity in the exhaust system. If the exhaust is too big, the gasses slow down, and fowl up the flow through the head.

I know this is a gross oversimplification, but hopefully some of the gurus around here will have more to say.