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Old 02-20-2013, 02:33 AM   #31
RGregor
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Quote:
Originally Posted by chasbmw View Post
Rudi, how easy is it to get away with a non stock exhaust in Germany? Do people run what they like and then go back to stock when the bike needs its inspection?
What is legal or can be legalized depends on several aspects.
The law says that your bike must fulfill the restrictions being valid at the time when it was first brought onto the road.

Having a pre '81 bike you almost have no trouble at all.
I run my bike with open bellmouths and Norton style mufflers, so it is rather loud when I push it.
But I had it inspected and it was within the then valid limits. So it's all legal and registered in the vehicle documents. You have to register all changes made to the bike. As literally no part of my bike is stock any more I needed some additional sheets for the documents ..

In '81 limits were lowered.

From 1989 on things are different, according to the law you need to be within again lowered noise and newly introduced emission limits.
So 1988 GS frames are rather rare over here :-))

SR-racing however have certificates for their exhausts proving that they conform to the restrictions. Quite a few people wonder how they got them as the exhausts are not really silent ...

Changing back for inspection is a way to cope with the limits, but it won't help you when the police stops you. In the Munich area where I live they were rather rigid against the Harley guys with their loud and slow bikes.

Police stopped me once and asked, if exhaust was stock. I showed them the entry in the documents.
Next question was: how much does a bike like that cost?
We had a nice chat then for a quarter of an hour.
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Old 02-20-2013, 02:37 AM   #32
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Quote:
Originally Posted by chasbmw View Post
Jim Cray had Keihans make up some absorption type straight through silencers to his design.

They look almost stock, but sound like a BSA twin on Goldie silencers. Jim did a back to back dyno run using a dual plugged but otherwise stock R100/7 and the results show a useful increase in power throughout the rev range.

Here is a copy of the dyno chart, it's not that clear but I'm sure you will get the message. Keihans still make batches of these from time to time, or Jim has some in stock. 38 and 40mm.
Some guys here run these mufflers.
I don't think anyone has dynoed them. Thanks for the charts.
I remember that Dirk Scheffer used and recommended them for a while.
I knew this chart here (which was taken with a bike modified by Dirk Scheffer):
http://www.boxup.de/images/DiagrammWEB.jpg
But here it's not clear what modifications the engine had.

RGregor screwed with this post 02-20-2013 at 02:54 AM
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Old 02-20-2013, 12:37 PM   #33
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Quote:
Originally Posted by RGregor View Post
No, not necessarily. The engines I know (with the SR exhausts) have more low end torque than stock airheads have at their peak.
But this of course may be due to the other modifications. Including cam.



Now, these guys did some cross comparison (e.g. to the exhausts from this guy here
http://www.rs-haslauer.de/tuningteile_bmw.php ).

And the answer is that there is no definite answer.
Although the engine specs were similar the engines responded differently to different headers (crossover/no crossover) and mufflers.
Like I said, almost any setup will cost you low rpm torque with a STOCK engine. Don't forget that most wheel dyno charts START right around half way through our stock rev range.

I didn't see any airheads on that link?

I can believe that about modified engines having more low rpm torque than a stock engine's torque peak. My engine with a 336 cam had almost a flat curve all the way across to over 6500rpm. Now it has way more midrange and low end than it did then but I haven't run it on a dyno yet. I am going to break it in a bit more.

supershaft screwed with this post 02-20-2013 at 01:06 PM
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Old 02-20-2013, 01:24 PM   #34
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Quote:
Originally Posted by supershaft View Post
Like I said, almost any setup will cost you low rpm torque with a STOCK engine. Don't forget that most wheel dyno charts START right around half way through our stock rev range.
OK, I didn't get this right.
The dyno charts I saw started at around 2500 rpm.
But more important is I rode the bikes and listened to my butt dyno.

Quote:
Originally Posted by supershaft View Post
I didn't see any airheads on that link?
Probably they make more money with the modern bikes and advertise these.
They make 2-1 systems for airheads, but contrary to SR-racing their headers do have one crossover in front of the engine.
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Old 02-20-2013, 01:40 PM   #35
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The dyno chart posted in this thread is a lot more closer to what I usually see.
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Old 02-20-2013, 04:28 PM   #36
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Overland in Melbourne make a 2 in 1 at a sensible price.

I found one stock muffler didnt flow enough for a 2 in 1 and 900cc s, but a low cost Dunstall Decibel does, and looks and sounds a lot better too.

I wouldnt get to excited about equal length headers , while they might show up better at a few spots on a dyno you probably wouldn't notice the difference from unequal in normal road use.
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Old 02-20-2013, 11:05 PM   #37
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My first 2 into 1 was a nasty thing I cobbled together, and was unequal length, this was just a test set that was on for over a year. Then I made the equal length, and no difference in performance....I just think equal length makes more sense.
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Old 02-21-2013, 12:04 AM   #38
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Quote:
Originally Posted by supershaft View Post
The dyno chart posted in this thread is a lot more closer to what I usually see.
Yes, dyno charts are a story of their own. I think you said that once or twice.
And you're right.
Looking at the charts shown in this article you see the hole in the torque curve at around 3000 rpm (version 3).
http://www.advrider.com/forums/showp...1&postcount=41

This seems to be characteristic for the SR-racing exhausts as I've seen it quite often.
On the dyno charts taken at SR racing you won't see it as they usually start at 3000 rpm or above.

Never believe the charts of the man who wants to sell you something. Or prove the result of his work.

The charts I was talking about were taken on an independant dyno. And the level in the hole was still in the 80Nm range.
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Old 02-21-2013, 01:37 AM   #39
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Hi all,

found this thread by accident - very nice forum with a lot of good technical discussion !

Beemerboff - yes you are right when it comes to a BMW 2V street / sport engine in the range below 100 HP an unequal designed header can even have some pros ! It makes a much more flat power and torque curve and cleans out the peak spots. The max levels are more or less the same if the package is sorted out right. The most important coherence is to find between cam and exhaust.

If you start using cams with more and more lift at TDC your system starts to get more and more reactive to what happens in the direct periphery. In other words using the exhaust gas energy to motivate the fresh gas side the correct header design as well as the length on the carb side gets essential.

Also a right placed and dimensioned interference can be of great help when it comes to the search of low end torque.

If you know how....80HP and 90NM are easy to find in a std. R100GS engine.

You will not be in need of very much or fancy material just a cam and a header -
the std. silencer works fine up to 80 - 85 HP !

Very much of importance is the right modification of the squish band - at this point please know that you do not need to buy the 70 HP hc pistons, the 60 HP ones to be found in all R 100 GS / R will do the job perfect.

Air cooled for ever !

Dirk
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Old 02-21-2013, 02:10 AM   #40
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Dirk , have you any details of your squish band modifications - good information is hard to find.

There are people claiming they run 26 thou clearance with no problems, and others who claim that anything less than 65 thou and the piston hits the head, and everything in between.

And no one has any detail of what they do at the back of in particular the inlet valve, maintaining the squish band here would appear to shroud the valve.

The 2 in 1 on my stock cammed 900cc R75/7 is just about as unequal as you can get , with the LHS twice the length of the RHS, and the Dunstall Decibell works better with this set up, but I suppose I don't really know if it better flow of better harmonics, I had just assumed that because it flows better that was where the improvement came from.
Big mistake on this forum- you dont get away with much here!
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Old 02-21-2013, 05:23 AM   #41
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Squish band reloaded

Xxxxx?,

The squish makes the engine !

You should give much attention to this theme.

At the end best possible done it makes all gas which was sucked into the combustion chamber to be catapulted into the center area and there it can go to its controlled ignition making max possible power and torque.

Atomization is also important and if it works you will find no pinging at all even with high static compression ratios.

So under the line when you where able to gain voloumetric efficiency by doing good ports, valve seats, cams, exhausts you can loose a resonable percentage by a shitty squish.

My favorite set up for a R100GS street sport engine is:

Modified std. pistons

Conrods 1,5mm longer then std. - from 135 to 136,5 mm

Aluminium head gaskets; thickness in accordance to the heads - std. or reworked by someone before on the sealing surface.

Clearance adjusted in a range from 1,0 to max 1,5 mm - depending on some further issues.

Attn. :

The clearance is only one part of the story - the size and shape of the squishband has to be focused very much. It differs from bore to bore, stroke to stroke and from application to application.

Cam: EM2V1

Combined with a propper working header you have a very good performing setup.

Remaining with best regards from Essen

Dirk
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Old 02-21-2013, 06:13 AM   #42
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Dirk's advice accords with the work that jim cray did on my 82 RT, which in the euro version then still had high compression pistons, the pistons required replacing and his advice was to use low compression pistons and rework heads and barrels to result in a working squish band.

This is also the same as work that Moorespeed does with his replacement pistons

What is a 'EM2V1' cam?
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Old 02-21-2013, 07:46 AM   #43
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Quote:
Originally Posted by chasbmw View Post
What is a 'EM2V1' cam?
http://www.wunderlich-bmw.com/shopart/8510020-2-1903/shop/Parts-pool/8/Nockenwelle-EM2V1-asymmetrisch.htm
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Old 02-21-2013, 08:42 AM   #44
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Now, that's a poor translation of the german text ...
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Old 02-21-2013, 08:49 AM   #45
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I do have one of these hanging on the wall for that future build If it ever comes. I may sell it.


Quote:
Originally Posted by bone13 View Post
While no longer available these occasionally pop up used (and I never seem to have available cash when they do)
Supertrapp made a sweet 2 into 1 (used to have one and I would LOVE to find another one someday)
and Luftmeister made a pretty good 2 into 1, years ago.

I just lucked into one of the luftmeister's (which I need to go pick up) recently that I intend on using for a cafe project.
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