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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => Project Custom Motobricks => Topic started by: PiotrK100 on September 15, 2014, 10:08:53 AM
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Hi. I'm just preparing all my stuff for winter time to make my project started. It is K100rs from 1985 and I have a common overview what I want to do, but one thing is driving me crazy....exhaust. I do not know how to change it, possibilities, how much, how come, maybe from another motorcyckle. I need help in that matter the best with pictures.
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Why do you want a different exhaust?
Why is this driving you crazy?
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http://www.ibmwr.org/ktech/dyno-update/index.shtml (http://www.ibmwr.org/ktech/dyno-update/index.shtml)
Link shows no real improvement in performance when the stock exhaust is swapped out.
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What the dyno can't show you is the acceleration improvement gained by losing 3/4tonne of exhaust weight :neener:
You can change the exhaust for the noise, for the look or for the weight - but if you are intending to change it for performance you are kidding yourself. The stock exhaust is nowhere near the restrictive part of the whole.
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Staintune, Luftmeister, Mac, all made systems for the K100. Good luck finding one today. Check ebay, beemerboneyard.com, ibmwr.org, with patience you may get lucky.
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Well, I have not very much budget for my project so mus be very carreful with expences. I meet a guy yetsreday who do exhaust for bikes proffessionaly and he told me that first we'll try to cut off in majority original exhaust and bend it up. If that wont be possible he'll weld everything from scratch. :clap:
Of course that brings another problem with rear sets, so must figure out where to get proper sets. The final project will be for two person ride so foot rest for passenger are welcommed.
Now my brick looks like that: See attachment 1
And attachment 2 shows more or less the basic outlook of my project. Of course sets has to be changed.
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Go for it ............... MY exhaust showed a 9 bhp improvement with no other mods [ note for PDG ]. Instead of sounding like a strangulated fart, the exhaust note took on a purposeful and not over loud note. As noted - the weight saving alone is worthwhile.
To specifics. I made several exhausts - the one in my posts is about the Mk3 version. I did several that allowed for stock footrests, tragkorbs etc.
The base design was the same in all cases. Chop off [ K1100 ] or disconnect the downpipes. I then had the downpipes polished before having a collector made - then silencer of choice. I even had some prototypes made up using a cone design, but there was insufficient interest [ serious intent ] to make a minimum order of 10 sets.
My Mk1 - 3 had the collector welded to the downpipes, but the cone version allowed for bolt on application [ as OEM ].
My final design was a pure underseat ......... but then decided I didn't like it !
Shouldn't be a problem for your tame exhaust man - my Mk1 prototype cost me just under £100 [ $160 ?? ]
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Go for it ............... MY exhaust showed a 9 bhp improvement with no other mods [ note for PDG ]. Instead of sounding like a strangulated fart, the exhaust note took on a purposeful and not over loud note. As noted - the weight saving alone is worthwhile.
An actual quantifiable number? Are you feeling alright? :neener:
Anyway, because my job appears to be official nitpicker, I shall continue... 'An' increase isn't really a surprise, especially if it's at high revs - it's 'how' the increase happens that is important. Where in the rev range was the increase present? Did you lose out anywhere in the band? If you gained 9bhp above 7,250rpm, but lost 7bhp between 2 and 4k, then it would actually be less usable on the road imo.
If however you managed to, say, keep the p/t curve the same up to 6k, then had a peak power increase you did very well indeed and in that (or better) case I will very happily stand corrected.
As a general 'rule' (with exceptions and limitations), a free flowing large bore pipe will produce more top end power at the expense of low- and mid-range torque, while a seemingly 'more restrictive' small-bore system will perform better at lower speed while 'strangling' the engine as the speed increases. Most 'sports' exhausts claim (and usually deliver) power increases (on any engine - car, bike, tractor, etc.) but it's almost always at peak power - near or at the redline - fine if you intend to be running like that most of the time (for 'sports' for example) but around town?
As with any 'tuning', it's down to use and what you are prepared to live with. I rode a bike some time ago that had a nitrous shift system and lock-up clutch. The 1/4mile times were massively improved over stock and it was hugely entertaining, but for 'normal' road use it was almost unbearable. A highly strung, peaky, rev-happy engine is great fun to ride as a toy, but for everyday transport it very quickly becomes hard work.
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I chopped off more then 1/2 of my factory muffler and removed 2/3 of the original internals and it sounds pretty good considering that at the moment its essentially a blown out exhaust. Opionions were mixed on the sound when I did it, but no-one suggested returning it to stock.
When I pointed out that ill be adding a baffle back in and reinstalling the endcap, everyone generally agreed it should sound good.
It currently sounds A LOT like the bike in the "1986 bmw ghetto exhaust" YouTube video
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PDG - nitpick away :2thumbup: !!!!!!!!!!!
I call it serious debate, and even after spending all my working life [ 50 years ] in the business of building and selling competition engines [ car and bike ] and replica sports cars to go with them - I am still learning. You can't do that without listening to the views of others.
My area of expertise is predomimantly V8s - and I've built and raced my share over the years. Bikes have always been my hobby - firstly circuit racing, sidecar racing and then Drag Racing [ via Sprinting ].
We saw a gradual build up of bhp gain [ dyno ] with no other changes. We did this deliberately to answer just the question you [ and we ] pose/d. And you are correct in assuming there was a smaller increase [ but not loss ] in the lower rev. ranges. The fat part of the curve increase was from 4,250 up.
It is well known that our Bricks were strangulated at the factory in order to reduce the bhp initially available to improve reliability / longevity.
There were no "downsides" to the exhaust swap - gas mileage was around the same, warm up, idle etc. all as the stock Kay and no "peakyness" riding around town.
Here's Ben Kingham with one of my early exhausts - he won the B.E.A.R.S. Championship outright in 2013.
(http://i1213.photobucket.com/albums/cc472/manfredvonheyda/BKweb_2VSa0508-1.jpg) (http://s1213.photobucket.com/user/manfredvonheyda/media/BKweb_2VSa0508-1.jpg.html)
(http://i1213.photobucket.com/albums/cc472/manfredvonheyda/k100_mountain_2012_zpscb206433.jpg) (http://s1213.photobucket.com/user/manfredvonheyda/media/k100_mountain_2012_zpscb206433.jpg.html)
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We saw a gradual build up of bhp gain [ dyno ] with no other changes. We did this deliberately to answer just the question you [ and we ] pose/d. And you are correct in assuming there was a smaller increase [ but not loss ] in the lower rev. ranges. The fat part of the curve increase was from 4,250 up.
It is well known that our Bricks were strangulated at the factory in order to reduce the bhp initially available to improve reliability / longevity.
There were no "downsides" to the exhaust swap - gas mileage was around the same, warm up, idle etc. all as the stock Kay and no "peakyness" riding around town.
I was under the impression that the 'detuning' was much more involved than just the exhaust (in fact, I'm still positive it is) - cam profiles, injection and ignition maps etc. are all on the tame side and IMO the exhaust is the least of the evils...
Out of interest, which version of the 4cyl exhaust was the comparison against?
I'm of the opinion that the 75 system is 'better' from the factory than the 100/1100 one as well. It's a better match to the flow of the triple, plus it has equal length headers - combined with a couple of other minor mods that may (or may not of course) make it a worthwhile addition on the IL4.
I've seen quite a few 'sports' exhausts, and it's extremely rare to find one that performs well anywhere other than at 'headline figure' of peak power. For competition/racing/similar this might not be a problem, but for me having a lumpy, boggy poor idling p.o.s. isn't my idea of a road bike. As it seems you have managed to retain the rideability (I assume, given that you state no losses and no silly peaks - gradual increase) then it's a job well done.
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I HAVE A BOOK SOMEWHERE WITH THE SPECIFICS OF THE "FACTORY DETUNE" [ oops caps lock off ] - I'll dig it out sometime.
The stock exhaust in this case was the OEM 1984 version [ in VGC ]
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Anyone know what material the stock exhaust is made out of? Mine was so ugly that it doesn't even seam like it could be 300 series stainless
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I have NEVER come across one that isn't stainless [OEM]. Stick a magnet on it - or not, that will tell you the answer.
HOWEVER fuggly the downpipes are - they WILL polish up. My tame polisher charges me £10 [ $16 ? ] a set.
Where are you located ? If you are in the US - you will have hundreds of specialised exhaust companies that will almost certainly have a collector somewhere near right.
The "cone" style [ my second pic ] is dead easy to manufacture, and you can put the outlet at whatever angle you want.
Incidentally, that showed about the same increase in BHP [ 1bhp less ] as the traditional collector.