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Author Topic: Midpipe modifications  (Read 532 times)

Sparrow40k

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Midpipe modifications
« on: April 19, 2017, 04:15:46 AM »

Hey guys, I was just wondering how my 2012 GT650R would run if i cut my midpipe shorter and completely removing the second connection that joins further down then welding it up. Used a photo to try and explain my plan. I just want to check with the community first in case I destroy my bike- as I can see that the airflow doesn't look great on that connection further down as it isn't very curved.



Thanks in advance guys!
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BikeBandit.com

umop-ǝpisdn

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Re: Midpipe modifications
« Reply #1 on: April 19, 2017, 06:50:28 AM »

I think it is formed that way to keep the length of the exhaust headers equal. Your rear exhaust distance would be shorter and more restrictive due tpo the sharp bend.

To make an under bike exhaust practical, you might need to shift the assembly forward a bit. make the front header pipe shorter and then cut the midpipe 10cms or so in front of where the balance pipe joins and re-attach the flanged join.

You could then form the pipe as per your picture, but you would still need a balance pipe before the two pipes join. Not easy, but with the proper skills, workable.

Would look stunning though. Hope you figure it out!
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Sparrow40k

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Re: Midpipe modifications
« Reply #2 on: April 19, 2017, 07:07:19 AM »

Does a GT250 have a different pipe because I recently found this video of pretty much exactly what i am attempting myself: https://www.youtube.com/watch?v=ruwC_MCc7f0
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albertinhouston

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Re: Midpipe modifications
« Reply #3 on: April 20, 2017, 05:05:04 PM »

the 250 is def. different.
It has a weird collector box.

just throwing it out there.... what would it really hurt if the exhaust weren't balanced?
couple of HP? burnt valves??? weird exhaust sound???
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Dojy_biker

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Re: Midpipe modifications
« Reply #4 on: April 21, 2017, 02:56:48 AM »

i went to the extreem of making my own system. Rear pipe is connected, but front downpipe still on bike. and yes, i went DUAL rear pipes :)

Here is a picture of the NEW collector (lamda sensor mount underneath and not visable from this angle)


if you want to work out the complicated flow and pressure calculations , you can make a system without the link pipe. BUT, its silly to just chop it out of a stock system and leave the rest as is.
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Sparrow40k

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Re: Midpipe modifications
« Reply #5 on: April 21, 2017, 05:41:11 AM »

That pipe looks perfect !! Thanks for sharing
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Dojy_biker

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Re: Midpipe modifications
« Reply #6 on: April 21, 2017, 05:47:14 PM »

basic rule of thumb is if you use the same diameter pipe, they both want to be the same length.
Very rough calculations is : for every 30' bend make that pipe 0.5" shorter then the other. (measure the length of 90' or greater bends from the outer radius

if you have EFI, then the pipes would be ideally joined together 4" (minimum) before the lamda sensor (i only managed 3.5" but works ok)



there are other more complicated maths involved if you wanted to use different diameter pipes, but the average user doesnt need it that level of accuracy.
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Dojy_biker

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Re: Midpipe modifications
« Reply #7 on: April 21, 2017, 05:50:50 PM »

what would it really hurt if the exhaust weren't balanced?
couple of HP? burnt valves??? weird exhaust sound???

wouldnt run as smooth low down, one cylinder may run hotter due to increased back pressure and burnt valves are possible, definate loss of power .
« Last Edit: April 23, 2017, 11:16:11 PM by Dojy_biker »
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