Exhaust Restriction and Loudness

TallPaul · #1 (**permalink**) 12-09-2007, 08:04 PM

In general it would seem that the freer flowing an exhaust, the louder it would be. Sure there are exceptions, such as noise cancellation technology and rice boy noise maker exhaust tips, but for general exhaust work that us normal folks do, it makes sense that quieter = more restriction and louder = freer flowing. So is it a reasonable assumption that if you modify your exhaust and it gets louder, that you therefore have a freer flowing system?

whitebassbenny · #2 (**permalink**) 12-09-2007, 08:18 PM

you could get a high flow cat and a different muffler.

kens64 · #3 (**permalink**) 12-09-2007, 08:49 PM

Not always true. You can get really loud with glasspacks, but some glasspacks are restrictive.

But generally you are right.

Bear River · #4 (**permalink**) 12-10-2007, 12:43 AM

And the Magnaflows are among the least restrictive, and often they are amazingly tame sounding.

TallPaul · #5 (**permalink**) 12-10-2007, 09:13 AM

Yeah, so a tough and dirty rule of thumb, louder is freer, but not necessarily.

Well I figure the cat is a restriction, but so is the muffler. And if the change to a performance muffler makes it louder, then some restriction was relieved, though more could be relieved if the cat were changed too.

kens64 · #6 (**permalink**) 12-10-2007, 11:29 AM

Depends on the year. Newer cats flow well enough that a high flow cat will sometimes show little to no gain.

If the cat has lots of miles on it or is very old, then better gains could be realized.

Bear River · #7 (**permalink**) 12-10-2007, 05:25 PM

Why would mileage have anything do do with anything? Some of the earlier converters were more restricitive, but mileage is irrelavent.

TallPaul · #8 (**permalink**) 12-10-2007, 08:13 PM

I would guess the mileage thing is assuming that more miles = more deposits in the converter = more restrictive. But do deposits collect in the converter? It supposedly runs very hot, perhaps too hot for deposits.

kens64 · #9 (**permalink**) 12-10-2007, 09:20 PM

Parts dont live forever.

Bear River · #10 (**permalink**) 12-11-2007, 10:18 AM

Moving parts don't last forever. A catalytic converter is not a moving part. My experience, is they will last at least as long as the vehicle so long as the vehicle is maintained correctly. My dad still has his original converter on his Ranger and his Prism, bot vehicles have over 300,000 miles and both easily pass emissions.

In order for a converter to fail, their either has to be something wrong with the engine which causes the converter to overheat or plug up, or their has to be a design flaw to begin with that causes physical damage to the substrate.

kens64 · #11 (**permalink**) 12-11-2007, 06:58 PM

And in my experience, the inside of the cat we took out of my Dads Ranger actually fell apart when I set it on the workbench. Ran fine AND passed emissions as well. The truck runs clean enough to pass without the cat. Less than 100k.

Didnt mean the cat was good though. This truck was maintained better than 99% of the vehicles out there.

Bear River · #12 (**permalink**) 12-11-2007, 08:29 PM

I deal with over a thousand dead converter per month, and the vast majority show signs that they were either melted, plugged up, or rattled loose. Rattled loose is sometimes caused by physical damage, but more often is a design defect. It sounds like you fathers meets that criteria. It fell apart because it was already broken because the packing around it failed. Failure of that kind is not related to mileage, they can go anytime, be it 10,000 miles or 1,000,000 miles. It is related to heat however, heat causes the packing to fail if it of low quality (which most are) and when combined with excessive size (many OEM designs meet this criteria as well) it causes and expansion differential which gradually damages the packing.