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Vendor / bronze
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Discussion Starter · #1 ·
Here at Thunder Works I am working on a performance package deal. (Intake plus fuel controller plus exhaust). I am wondering if anyone has run a Dyno before and after removing the cat? I can't find anything here on the forum so far. We all know it reduces heat. Since removing it would increase flow I assume it could be helpful for more power. But we all want numbers. If no one has done it I will do it myself. It is just a hassle and expense so I am hoping someone else has actually done it.
 

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Read about this a while ago. Modern catalytic convertors hardly cost engine performance and hardly restrict flow.

Flow restriction is more caused by the airbox, and the exhaust doing it's job to keep a bike quiet enough.

Exhaust manufacturers often display dyno chats with before and after dyno runs, typically showing stock, aftermarket with stock fuelling, and thirdly aftermarket exhaust with a ECU flash. Often showing a noticeable gain. What you hardly see are dyno graphs from before and after an ECU flash with a stock exhaust.

Here's a nice graph however (from a non-Indian btw), both with stock exhaust. Just a reflash.

Text Line Plot Font Diagram


My take from this: proper fuelling is more important than just removing the cat.

(there's still a weight and heat advantage by removing the cat, but it's not a must do performance mod imho)
 

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Here at Thunder Works I am working on a performance package deal. (Intake plus fuel controller plus exhaust). I am wondering if anyone has run a Dyno before and after removing the cat? I can't find anything here on the forum so far. We all know it reduces heat. Since removing it would increase flow I assume it could be helpful for more power. But we all want numbers. If no one has done it I will do it myself. It is just a hassle and expense so I am hoping someone else has actually done it.
Sorry Marcus, I have no hard numbers. But I did the "cat gutting" and then I did it again WITH a lateral divider to keep the exhaust gasses separate until they got to the back of the collector, essentially making the OEM cat body into two virtually separate pipes. My carefully calibrated ass-dynomometer was unable to detect any performance increase at all. But the internal divider may have made the exhaust note just a tad quieter.
 

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I gutted mine and added a Wimmer air cleaner at the same time so I had it re-tuned by the same guy and lost 2 ft lbs of torque and gained 2 hp but it is hard to say which of the 2 changes were responsible for the change. Was not noticeable from the seat. I later did freedom true duals and no tune but seat of the pants feels like a big drop in bottom end grunt, I shift a lot more than before. I have not tuned it again because I am still on the fence about installing the Lloyds 558 cams
 

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Discussion Starter · #6 ·
I am wondering if removing the cat actually hurts the torque a little bit. I plan to get Dynos before and after removing the cat. If this is true, I will put my cat laden pipe back in. I have two sets. I will of course post the results. I thought this was settled but it looks like they are being removed for heat reasons and the power aspect is not dealt with. However, I agree if the heat goes way down it is worth losing a little power. Please post any more info if you guys have it.
 

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"Does removing the cat increase power?"

No.

I am wondering if removing the cat actually hurts the torque a little bit. I plan to get Dynos before and after removing the cat. If this is true, I will put my cat laden pipe back in. I have two sets. I will of course post the results. I thought this was settled but it looks like they are being removed for heat reasons and the power aspect is not dealt with. However, I agree if the heat goes way down it is worth losing a little power. Please post any more info if you guys have it.
I've heard guys here say they lost torque removing the cat. I asked why and how and was told no back pressure equals less torque. I guess they removed their mufflers too? o_O I looked into this theory for days and seen and read a lot of info on "drag pipe sag". But, again, gutting the cat and leaving the mufflers on should provide enough back pressure to alieve the dreaded "drag pipe sag".

Anyway, I noticed NO loss of torque nor did I notice any HP increase. I did however notice less heat and better throttle response!

.
 
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