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Full catless = less torque ??????
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06-17-2015, 11:25 AM | #23 | |
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Why don't you prove to me that it will affect it negatively?
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06-17-2015, 11:37 AM | #24 |
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Everything I have seen points to catless downpipes making much more power over catted. Even ar design who sells both and pretty sure they make more money on the catted versions will tell you that catless >> catted >> stock downpipes.
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06-17-2015, 11:38 AM | #25 |
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06-17-2015, 11:38 AM | #26 | |
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Either way, I think we both agree that removing the 2nd cat is not going to lead to lower torque. |
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06-17-2015, 11:40 AM | #27 |
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No it won't; the bigger the pressure differential between pre and post turbine the more energy transferred through the shaft. So you really can't go to big with an exhaust on a turbo setup. At some point, a bigger exhaust won't do anything as the pressure differential can't get bigger. But at no time will too big of an exhaust post turbo cost you power. Anything that minimizes that pressure differential like a pipe that's too small or a cat is going to cost power.
Based on this thought, catless downpipes would make less power than catted ones and we all know that's not the case. There is even a power difference between the 3" downpipes and 2.5" ones even though they all taper down to 2.5". Simply because the 3" section allows the exhaust to expand more and there is more pressure differential. Even with a N/A motor, it's not loss of "backpressure" that causes low end torque loss, it's loss of scavenging. With a turbo, there isn't really scavenging. I only have one anecdotal data point that's relevant. A long time ago, I built a turbo setup for a car. With the OEM secondary cat in place and 2.5" exhaust, it made 270whp at 5.5psi (7lb wastegate spring). We then built a 3" exhaust and replaced OEM cat with 3" test pipe. 2.5" downpipe wasn't changed. Car immediately made 301whp and it hit 7psi on the same spring. No tuning changes, just exhaust. And I think it was an additional 20ft/lbs torque. We also pulled the exhaust and ran it open downpipe, it picked up another 5-6whp. Later on, a friend bought the setup and modified the downpipe to 3". I forget the numbers, but he picked up a few hp by going to the larger dp. Last edited by shadow191; 06-17-2015 at 11:50 AM.. |
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06-17-2015, 11:46 AM | #28 |
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So you're going to offer your opinion without backing it up? That's not how you debate my friend
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06-17-2015, 11:49 AM | #29 |
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BuraQ, why do I gain 30wtq from catless downpipes, but lose 30wtq from catless midpipes?
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06-17-2015, 11:50 AM | #30 |
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06-17-2015, 01:48 PM | #31 | |
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Read on forums, concluded from trends by multiple people on forums, remember from a test from someone else, remember from a test you did? No offense, but I generally take other people's word with a grain of salt. Many times I have heard people say, "It's better because butt dyno," but I'm the type of person who wants to test theories with an actual dyno. Testing has been drilled into me from FSAE, as EVERYTHING needed to be tested, reviewed, verified and documented. We were drilled on every change we made and why we made it. Can you please expand on what you have seen? Not trying to be harsh or anything, just genuinely interested!
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06-17-2015, 04:00 PM | #32 |
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Honeywell/Garrett states that the less restriction in a turbo exhaust the better, period. This isn't debatable, it's been known/established for a long time. I agree that his testing shows otherwise, I question the validity of the comparisons -there are a ton of variables to account for, no way would I assume it had anything to do with cats.
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06-17-2015, 04:28 PM | #33 | |
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I would do testing on the 335 if I could, but the amount of time it takes to remove/install DPs on the xi is way too much to justify curing my curiosity. If Im wrong, Im wrong and thats cool. You learn things everyday. |
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06-18-2015, 05:57 AM | #34 | |
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06-18-2015, 10:06 AM | #35 | |
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This
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06-18-2015, 09:07 PM | #36 | |
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