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09-28-2022, 01:57 PM | #1 |
Join Date: Mar 2022
Location: Eastern WA
Posts: 20
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Exhaust Upgrade Theory
It seems everybody claims a significant boost in power by upgrading their exhaust. I believe these claims. I understand a higher flow less restrictive exhaust will give a performance boost.
What is not obvious is why many of the aftermarket exhaust setups I see suggested would be any less restrictive than the stock exhaust? Like this one I am considering... suggested by moto taco... for the Hawk 250 as an example... https://www.amazon.com/dp/B07GYSLJMD...roduct_details It apears to be the same tube diameter and still has a cat... how does it make such a difference? Is it actually bigger ID diameter? Smother on the inside? Less bends? Is the cat less restrictive somehow? Is the baffle/muffler the key? Would it be better to keep the stock exhaust and remove the cat or would an aftermarket one with a cat still be better? Any suggestions for an aftermarket that comes without a cat? Maybe it exists... but if not it seems someone could make some money selling just a straight pipe "header" that mates with the stock mufflers!! |
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09-28-2022, 02:12 PM | #2 |
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Join Date: Oct 2016
Location: Houma, La.
Posts: 11,708
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You can remove the cat on the stock exhaust and achieve the same results. The aftermarket exhaust doesn't have the cat which makes it less restrictive. There is a perfect balance you need to maintain when doing exhaust. You want to have enough back pressure to keep the low end power. Less restrictive exhaust will move the power to the higher rpms and loose some low end power. I found my decat stock exhaust on my stock Hawk engine performed better. Once i did the porting and decking of the head the freer flowing muffler work better.
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2024 Linhai 300 ATV 4x4 2023 Lifan Lycan 250 Chopper 2023 Venom Evader 2022 Lifan KPX250 2020 Kawasaki Vulcan S (Sold) 2004 Honda ST 1300 2016 Black Hawk 250 (sold) Keihin PE30 carb,125 main,38 slow.Pod filter,ported & decked head 10:1 CR,Direct Ignition Coil,15/40Sprockets,NGK DPR8EIX-9,De-Cat,Dual Oil Cooler,Digital Cluster 2016 Cazador180 XL 2014 Coolster150 JerryHawk250.com My YouTube Channel |
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09-28-2022, 03:48 PM | #3 |
Join Date: Apr 2017
Location: Omaha, NE
Posts: 8,100
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75% of the power increase is the result of the catalyst being deleted, at least on the Hawk. The cat on the Hawk is horrendously restrictive. The other 25% would be the muffler.
I did the exhaust because I like having a stainless steel system.
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Hawk Information and Resource guide: http://www.chinariders.net/showthread.php?t=20331 2018 Hawk 250 - Full Mod list here. http://www.chinariders.net/showpost....62&postcount=1 2024 Royal Enfield Shotgun 650 https://chinariders.net/showthread.php?t=34124 |
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09-28-2022, 05:14 PM | #4 |
Join Date: Jan 2021
Location: Lehigh Valley Area
Posts: 165
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I felt a little more acceleration with an exhaust upgrade, but real benefit for me was better top end with ability to gear higher. Oh, I have a TBR7 btw.
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09-28-2022, 05:58 PM | #5 |
Join Date: Mar 2022
Location: Eastern WA
Posts: 20
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So maybe I've been making an incorrect assumption about the can looking thingy on the header. I have been assuming that is a cat.
If it's not a cat then what is it? Maybe an expansion chamber of some sort? |
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09-28-2022, 08:08 PM | #6 |
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Join Date: Oct 2016
Location: Houma, La.
Posts: 11,708
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On the stock exhaust it is the cat. On the after market exhaust it just there for looks. Fake cat.
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2024 Linhai 300 ATV 4x4 2023 Lifan Lycan 250 Chopper 2023 Venom Evader 2022 Lifan KPX250 2020 Kawasaki Vulcan S (Sold) 2004 Honda ST 1300 2016 Black Hawk 250 (sold) Keihin PE30 carb,125 main,38 slow.Pod filter,ported & decked head 10:1 CR,Direct Ignition Coil,15/40Sprockets,NGK DPR8EIX-9,De-Cat,Dual Oil Cooler,Digital Cluster 2016 Cazador180 XL 2014 Coolster150 JerryHawk250.com My YouTube Channel |
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09-28-2022, 09:58 PM | #7 | |
Join Date: Feb 2021
Location: Kansas City
Posts: 2,659
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Quote:
The ambiguous nature of these aftermarket pipes makes it impossible to confidently buy an exhaust system. The best way to avoid the confusion is to just gut the cat: https://www.chinariders.net/showthread.php?t=30235 Crude, yes. But in this case, I have created a power bomb ("resonator?"). |
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05-09-2023, 07:46 PM | #8 |
Join Date: Aug 2020
Location: Australia
Posts: 1,424
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The engine can't get much past 8000rpm so other than making a lot of additional noise the removal of the baffle doesn't really equate to noticeable additional power.
Though I don't have a stock hawk muffler... I did try a baffle/non baffle test on my Aussie Muffler and the non baffle was unpleasantly noisy and no power bonus to speak of. The DIY baffle mod did help a little with maybe 100-200rpm but that might just be me wishing it to justify the work done to 'improve' that original configuration. I have noticed the muffler section does not appear to be pushing off the head pipe slip coupling, which to me suggests an improved flow rate and less back pressure. If you're using an unported head then a de-cat would be more than adequate to help the engine breath better... |
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05-09-2023, 08:31 PM | #9 |
Join Date: Feb 2021
Posts: 997
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I , without a doubt can say that the Hawk benefits from just simply removing the cat, because all I have done to mine has been removing it. I had already removed the baffle/spark arrestor from the muffler,so I know the cat was holding it back. I have a TBR7 with full aftermarket exhaust, and I am pretty sure both my Hawk, and TBR7(both have 46/17 sprockets) are both really close to each other in power, although the TBR7'S smaller smoother tires gives it an advantage, but the cat removal from the Hawk did help the Hawk, in the same way that the full aftermarket exhaust helped the TBR7, which to me seems like they are not only happier, and less stressed at high RPM, but they pick up, and hold RPM better past mid range. There may be a little more to be had by working on the Hawk's muffler, because it's not really loud, but I would hate to go through the trouble, and not gain anything, and I like having my muffler guard, so I don't particularly want an aftermarket muffler.
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05-09-2023, 10:04 PM | #10 |
Join Date: Sep 2022
Location: Ohio Valley
Posts: 745
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Okay so then unless I just want to annoy folks, I should just leave it in there. Thx fellas.
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2022 Hawk 250 |
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05-10-2023, 08:12 AM | #12 |
Join Date: Sep 2022
Location: Ohio Valley
Posts: 745
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When I was driving my typical junk cars, which I've had my entire life, it used to annoy me that the cops would pull over cars with loud exhaust but let some incredibly loud motorcycles get away with it. But then I realized why. Usually, a loud car exhaust is due to a failure that could leak carbon monoxide into the interior, and I have, in fact, suffered from that when I was driving one. I'd get home after a long drive, and have a headache. That might be why half of my brain has atrophied!
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2022 Hawk 250 |
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05-10-2023, 12:55 PM | #13 |
Join Date: Sep 2022
Location: Ohio Valley
Posts: 745
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okay so I had to try it anyway. I took out the baffle and it made the bike louder and also screwed up the throttle response..immediately. so back in it went. sometimes you just have to learn the hard way. i still have stock carb so maybe it got even leaner?
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2022 Hawk 250 |
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05-09-2023, 11:02 PM | #14 |
Join Date: Feb 2021
Posts: 997
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http://At the bare minimum,you should remove the cat. If you do just that, it will be just barely louder than it would be with the cat, but the bike will be healthier. The small diameter cats are VERY restricted, and probably why similar bikes in countries that don't have strict emission standards produce more HP , than the lean jetted, and restricted exhaust bikes we get. I am posting a couple pictures of the Hawk cat, that I removed. On top of it is a quarter for reference. The diameter of the cat is small, and the pipe is thick walled to boot.http://
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05-10-2023, 02:38 PM | #15 |
Join Date: Apr 2017
Location: Omaha, NE
Posts: 8,100
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Stock carb = Too lean to begin with.
Stock carb with any exhaust mods = way too lean. You need to jet the carb or wait until the nibbi comes in.
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Hawk Information and Resource guide: http://www.chinariders.net/showthread.php?t=20331 2018 Hawk 250 - Full Mod list here. http://www.chinariders.net/showpost....62&postcount=1 2024 Royal Enfield Shotgun 650 https://chinariders.net/showthread.php?t=34124 |
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