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I'm not sure that it is that simple. I have dyno graphs for 107 ci. bikes that are set up close to the same. The first one is using a stock decatted header with stock mufflers with Full Sac 2" cores and big sucker air cleaner. The second one is using a Full Sac MX head with stock mufflers recored with 2" & 1.75 " cores and a heavy breather air cleaner. Both are running TTS 100 cams. They are different bikes and different dynos, but the results are very close to the same.
Then there is this from Fuelmoto. A 107 with Jackpot mufflers on a stock header vs. the same bike with a Jackpot header, Jackpot mufflers, and a better air cleaner. The first bike is still running the cats. So again, not apples to apples. The better air cleaner is probably good for 2 or 3 ft/lbs. and the removing the cat would probably gain 2 or 3 ft/lbs. So take that into consideration and they are pretty close. Also, looking at the stock bike dyno and the stock bike with mufflers and a tune, the gain was 3 ft/lbs and 3 hp.
As for a 2 into 1 out performing a 2/1/2, here are a couple dynos of the same bike, same dyno, different exhaust.
So what it boils down to is that a full system, 2 into 1 or 2/1/2 with mufflers, will cost $1000 to $1500, along with a tuning device of some type, $300 to $1000, and maybe a dyno tune, $400 to $600. Mufflers and decatting the stock head pipe, less than $500 and I have done this without tuning. Is the gain worth the cost?
my guess is these differences would be more significant with an increase in displacement or a more aggressive cam. Intake and exhaust go hand in hand.
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