I called the tech dept at the IMCO factory in Texas. They are one of the best builders of "traditional" glasspacks in the USA. They make all sorts of sizes and products.

http://www.grabthepower.com/products-front.asp

1) They said glasspacks do not clogg or cause additional resistance overtime.
2) The life expectancy varies. Some people still have the same glasspacks for over 20 yrs. Just depends on how much you drive, rust factors, etc..
3) Putting a glasspack in backwards does not affect flow or sound of the system.

 

I almost would have to disagree on mounting them backwards. A few years ago a few buddies of mine had almost the exact same old chevy truck, and they both got dual exhaust with some glasspacks. Long story short one of them mounted one "properly" and one backwards, and the one mounted backwards was louder. But who knows if thats why.

 

Mounting (louvered) glasspacks backwards definitely makes a noticable difference in sound. When you mount them backwards the exhaust is passing over the louvers instead of into them.

 

I agree. The only way its not going to change volume is if the core is preforated (sp?) and not louvered.

 

According to the Tech Dept at IMCO, they have tested their glasspacks on a flow bench and found that they got the same flow results with the glasspacks forward and backwards.. As far as the sound goes, They said it shouldn't make much difference.

Forwards= exhaust flows over the louvers
Backwards= exhaust flows into/against the louvers, thus making more turbulence

Preppypyro - sounds like you did a "mythbusters" and found the truth.. Did the louder truck not only have more volume, did it sound better overall?

 

Well it sounded different. It was louder, but the quieter one sounded really good too. It all depends if you like it louder or quieter. Myself I preferred the quieter ones, had a little bit more of a rumble then a raspy sound to it.

 

I thought I would add somthing here, I was on Heartthrob's site and they say that when you mount a louvered glasspack the exhaust should in fact flow over the louvers and not into them. Imco getting the same results either way seems to show me that they have a perftube design. Louvers will cause slightly more restriction(not much but a slight bit) if the exhaust flows into the louvers and not over them.