BMW K bikes (Bricks)

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1Back to top Go down    Back pressure on Fri Mar 02, 2018 8:33 pm

timo27

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Hi all, has the subject of back pressure been discussed in the past? - 1985 k100

    

2Back to top Go down    Re: Back pressure on Fri Mar 02, 2018 8:41 pm

MartinW

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If you are talking about your spine you can change the handle bars.
If you are talking about your wind problem you can change your diet which will reduce the pressure.
If you are talking about your bikes exhaust, numerous tests have been done. OEM has the best performance least noise.
Regards Martin.


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K75s Hybrid
    

3Back to top Go down    Re: Back pressure on Fri Mar 02, 2018 8:54 pm

timo27

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So if loosing back pressure is a problem can i compensate for a drop - lets say by opening up the air intake or reducing the fuel pressure?

    

4Back to top Go down    Re: Back pressure on Fri Mar 02, 2018 9:02 pm

MartinW

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You need to post what symptoms you bike is experiencing. Why do you think you have a back pressure problem?
Regards Martin.


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K75s Hybrid
    

5Back to top Go down    Re: Back pressure on Fri Mar 02, 2018 9:05 pm

timo27

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I dont yet i'm just sure there is a reason the standard exhaust is so intricate - oh and yes its coming off.

    

6Back to top Go down    Re: Back pressure on Fri Mar 02, 2018 9:07 pm

timo27

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Its old Martin and to replace it would cost more than making a replacement.

    

7Back to top Go down    Re: Back pressure on Fri Mar 02, 2018 9:29 pm

MartinW

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There has been a lot of experimenting with various exhaust designs and aftermarket exhausts. And if you search there are dyno comparisons out there. The general conclusion is that there is no performance benefit to be gained.
Some might improve bottom, mid, or top end performance slightly but it will be countered by a loss elsewhere. If you are doing it just to create more noise then that will be achievable but at a performance cost. How much loss will only be determined by the design and by doing a before and after dyno. There are plenty of cheap OEM exhausts out there for less than it would cost to either make or buy an aftermarket exhaust.
Regards Martin.


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K75s Hybrid
    

8Back to top Go down    Re: Back pressure on Sat Mar 03, 2018 1:12 am

Point-Seven-five

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Unless your goal is more noise in an attempt to be safer, your best bet is to find a good used OEM exhaust. My K100RS came to me with a well known aftermarket exhaust that embarrassed me every time I rode through town.

I sold it and was able to purchase a very nice OEM exhaust for half of what I sold the aftermarket system for. My bike runs better at lower mid-range and uses a bit less fuel.And I don't cringe anymore at stop lights when I'm in town.


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Present:
1994 K75RT
1994 K75S
1992 K100RS

Past:
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

9Back to top Go down    Re: Back pressure on Sat Mar 03, 2018 3:31 am

MartinW

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Motorworks UK have pre and post 86 K100 mufflers for 50 UK pounds. Headers 45 UK pounds. A round trip of approximately 4 hours.
Regards Martin.


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K75s Hybrid
    

10Back to top Go down    Re: Back pressure on Sat Mar 03, 2018 5:29 am

charlie99

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old can look good , if you do the work

before



after



and will be required to adapt any thing to fit

check out ben kinghams work and parts he has to sell at bsk speedworks

http://www.bskspeedworks.co.uk/k-parts.html

just one of several places that make stuff for k bikes still today

good luck


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cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%O
    

11Back to top Go down    Re: Back pressure on Sat Mar 03, 2018 11:39 am

Born Again Eccentric

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Hey Charlie,

Do you do mail order? I could send you my oxidised, discoloured pipes (and OEM muffler) and you could send them back looking all shiny and new? Wonder what the postage cost to/from Oz would be?

I keep meaning to start cleaning mine up as part of my Donna rebuild, but it's too miserably cold out in the workshop at the moment (it is so well built and draft free (not) that, this morning, I found snow had been blown in under the eaves and had filled my toolboxes). I had already told myself off for bringing the engine block into the warmth of the kitchen to do some helicoil work as a result of a few stubborn fasteners and a little cosmetic painting (it's back in the cold workshop now)!


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Paul

"Heidi" K100LT 1991 (Grey) (VIN 0190172 Engine No. 104EB 2590 2213) - 5th owner. January 2014 (34,000 - 61,000 miles and counting....)
"Gretel" K100LT 1989 (Silver Grey) (VIN 0177324 Engine No. 104EA 2789 2211) - 4th+ owner. September 2015 (58,500miles and counting....). Cat C Insurancewrite-off rebuild Feb 17
"Donor" K100LT 1990 (Red) (VIN 0178091 Engine No. 4489 2024) - 6th & final owner (crash write-off now donor bike). June 2012 (73,000 miles) to November 2013 (89,500 miles)
    

12Back to top Go down    Re: Back pressure on Sat Mar 03, 2018 2:27 pm

Two Wheels Better

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Motad UK make a very nice (round) muffler for the Mighty K. I whacked one onto my RS about eight years ago, it's held up really well, and although there is a very very slight additional 'burble' to the note at idle it is not intrusive at all. Its performance level is essentially stock.

Now, Charlie has a sweet Staintune on his RT and it's a pleasure to ride a coupla dozen metres back from him listening to that sweet metal thang sing!


After six years it still had a sweet patina, and scrubs up well.


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1987 K100RS, Big Block '93 K11/K12 hybrid, '09 K1300GT, '07 K1200R, '04 R1150RT, '95 R100 Mystic, '77 R75/7.
    

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