Put CATS back in
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Put CATS back in
Failed CA Smog on my 08 with HFCs (first time testing)
Now the surprise part>>>
Car has BETTER THOTTLE RESPONSE (below 3K RPM) and SHIFTING IS SMOOTHER (in lift throttle) with cats back in. That's because RPMs drop off more slowly in shifting. It's noticeable and I don't think it's trivial either. If you cruise at 2500 3000 RPM and want to PASS or accelerate quickly, it makes a difference. Not saying HFCs don't add HP..they do. This is just my take on *daily driving* with cats back in. I didn't realize all this until a made the sudden transition back ..it really surprised me!
This isn't the old *low rpm torque* vs *high rpm torque * ..*back pressure*..*Scavaging* stuff, although those lurk as factors I don't wish to re-hash. Just an indisputable observation I have made personally. If I had to make an analogy, it would be somewhat like going from a light flywheel back to stock in that RPMS *HOLD UP* better and are slower to drop with the cats. I was surprised to see the car was more responsive and *drivable* than with HFCs in. Another factor could be that sensors (A/F and 02) are now working as they were supposed to. I noticed IDLE RPM is more steady now and doesn't *HUNT* like it did with the HFC. Yes, I miss the *growl*, but it was getting old and on the HWY it was always *there* (no drone). Car still has nice sound with Gemini Cat back and I actually enjoy the lower decibel experience. I will leave em in from here out.
Just my take. I know there aren't many who have driven with HFCs or TPs for several years and then went back to Cats.
Now the surprise part>>>
Car has BETTER THOTTLE RESPONSE (below 3K RPM) and SHIFTING IS SMOOTHER (in lift throttle) with cats back in. That's because RPMs drop off more slowly in shifting. It's noticeable and I don't think it's trivial either. If you cruise at 2500 3000 RPM and want to PASS or accelerate quickly, it makes a difference. Not saying HFCs don't add HP..they do. This is just my take on *daily driving* with cats back in. I didn't realize all this until a made the sudden transition back ..it really surprised me!
This isn't the old *low rpm torque* vs *high rpm torque * ..*back pressure*..*Scavaging* stuff, although those lurk as factors I don't wish to re-hash. Just an indisputable observation I have made personally. If I had to make an analogy, it would be somewhat like going from a light flywheel back to stock in that RPMS *HOLD UP* better and are slower to drop with the cats. I was surprised to see the car was more responsive and *drivable* than with HFCs in. Another factor could be that sensors (A/F and 02) are now working as they were supposed to. I noticed IDLE RPM is more steady now and doesn't *HUNT* like it did with the HFC. Yes, I miss the *growl*, but it was getting old and on the HWY it was always *there* (no drone). Car still has nice sound with Gemini Cat back and I actually enjoy the lower decibel experience. I will leave em in from here out.
Just my take. I know there aren't many who have driven with HFCs or TPs for several years and then went back to Cats.
Last edited by ronn1; May 23, 2014 at 11:08 PM.
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Yes..I had Osiris before putting in the Gemini...they said additional tune wasn't required for that mod. As far as adding HFC later, yes may have helped some..but I would have still faced the SMOG failure in Ca. I was told HFC wouldn't add more than 10HP tops and that would be at the top end...so SOUND appears the only reason in my mind for this mod. 95% of those who add an HFC (or TP) will never really utilize the modest PERFORMANCE enhancement unless they seriously track the car. With FI cars, it's a different story. As I mentioned, no point in going BACK to the HFC..even if I can pass smog next time. Not worth it for me and I actually enjoy the *new feel* of responsiveness and *quieter* exhaust note. Maybe it's my age showing now
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I'll have to dig around for my old dyno sheet, but after installing ART's I could definitely the difference (+8whp, +11tq). Power was increased through pretty much the whole powerband, not just up top.
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That's a personal thing. I liked the sound of the HFC, but it started to get *old*. Stock cats with a nice Catback can enhance the sound moderately and I find my Gemini cat back gives just what I want. It's all a matter of balance and taste.
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Found this article...funny how he found EXACTLY what I did when I put stock cats back in>>
http://www.gmtuners.com/gta/emission.htm
Another interesting article that compares 1) Stock Cat 2) Gutting cat 3) TP
http://www.importtuner.com/tech/impp...ct_or_fiction/
http://www.gmtuners.com/gta/emission.htm
Truth: From personal experience, the catalytic converter has been a blessing in disguise for me. After installing the unit(s) first on my 86 Monte Carlo, I immediately noticed how much more smooth the power band was. It seemed as though I had extra low end power without it affecting the top end grunt of my EFI 355 engine
Truth: Most older pellet-type cat converters were very restrictive, but these were virtually all replaced by the mid-80's with new rare metal containing honeycomb type units especially on V8 equipped GM and most other manufactures' vehicles. These new type converters are very efficient as long as they did not become damaged or plugged by lead and other non-converter safe fuel additives. Recent dyno tests have in fact showed that modern converters rob only about 3-8 horsepower depending on application. In many cases, the factory cat-back exhaust system robbed as much as 40 HP compared to an aftermarket, performance-oriented system.
http://www.importtuner.com/tech/impp...ct_or_fiction/
The Verdict:
Compared to our baseline runs, we were able to see no benefit of the hollowed-out cat versus leaving its catalyst core intact, and compared to the test pipe, there was no question; the gutted cat lost all around. Exhaust gasses became turbulent as they passed into the cat's open reservoir, actually increasing backpressure and hurting power. As we had suspected, replacing our car's cat with the test pipe cost a few low- and mid-range ponies and lbs-ft (bad for daily driving), but more than made up for it up top (good for race day). Bottom line: Keep the cat intact for the street, replace with a proper test pipe for the track.
Compared to our baseline runs, we were able to see no benefit of the hollowed-out cat versus leaving its catalyst core intact, and compared to the test pipe, there was no question; the gutted cat lost all around. Exhaust gasses became turbulent as they passed into the cat's open reservoir, actually increasing backpressure and hurting power. As we had suspected, replacing our car's cat with the test pipe cost a few low- and mid-range ponies and lbs-ft (bad for daily driving), but more than made up for it up top (good for race day). Bottom line: Keep the cat intact for the street, replace with a proper test pipe for the track.
Last edited by ronn1; May 23, 2014 at 10:23 PM.
It's harder to drive because HFC and TP give better throttle response. the RPMS will fall quicker and the Z is already a hard car to drive due to the clutch being so on and off.
You probably shouldn't get a lighter flywheel if you didn't like the HFC
You probably shouldn't get a lighter flywheel if you didn't like the HFC
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.
im waiting for my first smog to come up this year as well. I had Stillen HFC's and decided to sell for TP's once i found out that i will still fail smog even with them in...other than smell wth is the point? lol...smh
Need to find some OEM cats and get prepared for smog
ughh damn Cali
Need to find some OEM cats and get prepared for smog
ughh damn Cali
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