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SC Cat Bypass: My Butt Dyno Review
Just got done trying out the cat bypass on my otherwise stock 3.0 CIS, thought I'd share my totally unscientific results.
I thought it was running well before, but after pulling off the cat (which I had PB blasted several times over the past year in anticipation of this mod) and trying to see any light through/around the bend in it, I think it may have been in worse shape than I knew. I'm sure someday I'll go the SSI route, but I think this is truly the only CHEAP, noticeable mod we can do on these. Slightly more growl from the exhaust (cool) and seems to really breathe better below 3k, which is where the power band started before with the cat. More snappy, more responsive, and with only $80 in the pipe and $23 worth of new bolts I'm pretty satisfied. I knew it wouldn't suddenly act like a turbo, but it is (at least for me) a noticeable difference. '79, so no sensor. Hell of a lot lighter than the cat/shield, too! I'd recommend it to someone looking for a quick mod that won't break the bank. Funny thing: the day I got it all together, the DMV registration renewal arrived. "No emissions required" made me smile, though I already knew that... of course, I'll only use it "off-road"  Just my .02
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1984 928s 5 speed |
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06-30-2009, 10:34 AM
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Air Cooled Addict
Join Date: Aug 2007
Location: Brandon, FL
Posts: 272
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Hey Porschefool,
Glad that worked out for you. I've been on the fence about gutting my cat, since most feel that it reduces power over a pre-muffler or cat-bypass. Is it much louder? How much weight would you say you saved? TIA and happy driving!
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Joe V '84 Schwartz 911 Carrera 3.2 '91 Specialized S-Works M2 - Gone but not forgotten '12 Trek X-Cal : American Classic - XT brakes/shifters/derailleurs - carbon goodies '13 Trek Madone 5.2 stockish |
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06-30-2009, 12:38 PM
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Band.
Join Date: Dec 2003
Location: Denver, CO
Posts: 13,333
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My cat-bypass got me about 0hp on the unscientific butt-dyno, but I'm happy with the weight/heat reduction, for sure. And I can put it on the sniffer without screwing around.
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1983 SC Coupe 1963 BMW R60/2 1972 Triumph Tiger 1995 Triumph Daytona SuperIII |
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06-30-2009, 12:48 PM
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Registered
Join Date: Nov 2007
Location: N Charleston, SC
Posts: 66
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 This is my car, which is a 3.2, with a cat bypass, B & B muffler, and a Steve Wong chip. The other stock 3.2s that day were in the 180 hp range. |
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06-30-2009, 03:17 PM
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Registered
Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
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Another cheep thing:
Run a tank or two of injector cleaner throuth it. Put a timing light on it and verify your total advance at high RPM's. Then, put a clean air filter on and get it on a dyno to adjust the AFR to near 13/1 the best you can. With the exhaust change there is a chance you might be running lean. Just my two cents... The best. |
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06-30-2009, 04:15 PM
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Quote:
maybe more. Exhaust note only slightly more aggressive, not at all obnoxious and I love it. Haven't done the terrifying 6k full advance timing check for awhile, need to get to that and a valve adjust soon. |
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06-30-2009, 07:25 PM
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