Funny you should ask. I flunked miserably. - Saab 900 Bulletin Board - Saabnet.com
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Funny you should ask. I flunked miserably.
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Posted by JohnB (more from JohnB) on Thu, 5 Jun 2003 12:42:39 Share Post by Email
In Reply to: cat removal effects on HC & CO, Ed S, Thu, 5 Jun 2003 11:11:50
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with a cat on and operating with a 100-130F temp increase across the cat at 2500 rpm.
MD state standards 1.8GPM, I got 2.07GPM HC
30GPM standard, 14GPM Pass, CO
2.8GPM standard, 4.29GPM fail, NOX.
no CO2 standard, but it pulled 370.GPM (someday there will be a CO2 standard, just wait!)

The point is without a cat it would be much worse.
I haven't measured what it be with the new cat in terms of temp rise across the cat at 2500 rpm, but the emissions are very much cleaner with an aftermarket max-flo cat:

.1809GPM HC
.41GPM CO
.20GPM NOX
54.8GPM CO2

And judging from my dyno test, yes, the numbers drop off above idle simply because at idle you have zero miles and therefore infinite grams per mile!
There are regimes in which you have zero emissions too, because the FI cuts fuel flow, what, from 3400 down to 2200 rpm with throttle closed? or something like that. I'd have to look it up.

Still, I would suggest you get a max-flo cat...they're ostensibly similar to no-cat in terms of flow according to the vendor. They claim about a 7hp increase in a stock system with no cat, expecting about the same increase with their cat. However, with a 2.5" or larger cat back system you might get more with no cat (and maybe more with max-flo...I dunno when it, ummm, 'maxes' out...pun intended).


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