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Old August 19th, 2018, 04:09 AM   #1
$wim
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exhaust fabrication for 06 250r

looking for advice on possibly either fabricating a new set of mufflers, or a friend had said that I should gut the stock mufflers. but would that cause me to lose ot on horse power?
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Old August 19th, 2018, 03:30 PM   #2
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In my quest to lose weight on the bike and not in my wallet I experimented with making a 2 into one using stock head pipes and stock mufflers.

DSCF0003.jpg


this didn't turn out to well...lost 6 mph on my test acceleration strip, so next I ran a long drill bit down the exhaust exit, it made a little more noise but didn't pick up any mph on the test course. Next I cut the muffler apart at the front weld of the muffler (where the muffler and head pipe meet) and used a big punch to curve back the center hole I had drilled out, and removed the "screen" on the inside pipe.

DSCF0001.jpg


before

DSCF0002.jpg

and after.

this did pick up a couple of mph (and a little more noise) on the test course, but was still 4 mph slower than stock pipes and mufflers. After that I put on another set of stock head pipes and gutted another muffler (so it was dual pipes again) and walla, it was now 2 mph faster than it had been stock with a little more noise again, but easily streetable without getting the neighbors up in arms. So this gained a couple mph but didn't loose more than a few ozs.


My next step was to find a used Muzzy header. It was then 2 mph faster than my gutted mufflers and 4 mph faster than stock. All jetting is stock, I know everybody says you need to rejet, and we did the rejetting thing on two different pregens and they both are fastest with stock jetting. Jetting is still a tiny bit rich at wide open throttle but close enough. BTW we are at 1300 ft. above sea level.

ps: also running stock airbox and stock air filter
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Old August 20th, 2018, 07:37 AM   #3
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What you loose is torque . I found that short open exhaust cost about one or two ft lb of torque. Plus added noise.
Long pipes seem to be the best for scavaging. The best system I ever made was 57 inch primary pipes and long cones. Then a reverse cone at the end. I kept open I g the outlet until the power stopped going up. About an inch and a half .
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Old August 24th, 2018, 09:52 PM   #4
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Quote:
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What you loose is torque . I found that short open exhaust cost about one or two ft lb of torque. Plus added noise.
Long pipes seem to be the best for scavaging. The best system I ever made was 57 inch primary pipes and long cones. Then a reverse cone at the end. I kept open I g the outlet until the power stopped going up. About an inch and a half .
I probably won’t gut mine then, do you have any pictures or that 57 in primary with the reverse cone?
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Old August 25th, 2018, 07:32 AM   #5
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This is the exhaust
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Old August 26th, 2018, 01:39 PM   #6
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Quote:
Originally Posted by Racer x View Post
What you loose is torque . I found that short open exhaust cost about one or two ft lb of torque. Plus added noise.
Long pipes seem to be the best for scavaging. The best system I ever made was 57 inch primary pipes and long cones. Then a reverse cone at the end. I kept open I g the outlet until the power stopped going up. About an inch and a half .
Is that 57-inches before 2-1 merge? I think there's an optimum angle for the cones on exhaust. Need to look that up...
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Old August 26th, 2018, 03:02 PM   #7
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It is a twin exhaust system. 57 inch from the valve to the end of the cone. Then a four inch cone.
It is copied from a 500cc MV Augusta system in the Barber museum. Same bore and stroke. I figured they knew what the are doing since I don’t.
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Old August 26th, 2018, 08:02 PM   #8
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I'm designing 2-1 for pre-gen now. From what I can gather on various published studies out there, I want header pipes to be between 18-22". Then critical diameter and flow-rates of pipe and muffler after that. What failed on Z1R's experiment was he stuffed 2-cylinder's worth of volume & flow after merge into pipe and muffler designed for 1.

Going to use Tyga's new-gen design for diameters after merge. Appears to work well and better than some other systems on market with pipes that are way, way too large. Large enough for 150-bhp engines!
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Old September 11th, 2018, 07:16 AM   #9
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Quote:
Originally Posted by Z1R rider View Post
My next step was to find a used Muzzy header. It was then 2 mph faster than my gutted mufflers and 4 mph faster than stock. All jetting is stock, I know everybody says you need to rejet, and we did the rejetting thing on two different pregens and they both are fastest with stock jetting. Jetting is still a tiny bit rich at wide open throttle but close enough. BTW we are at 1300 ft. above sea level.

ps: also running stock airbox and stock air filter
I have a used Muzzy 2-into-1 header also. How did you finish the rest of the exhaust, midpipe and muffler, or did you just run the header?
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Old September 12th, 2018, 08:13 PM   #10
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no, I bought a complete system with the aluminum muffler
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Old October 6th, 2018, 09:57 AM   #11
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did you keep the OEM crossover on your head pipe?
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