2 to 1 exhaust

[motu]

I made my own equal length 2 into 1, and use an IDS2 Supertrapp on it. I think a 2 into 2 with short mega's sounds better, but they are too loud. The Supertrapp is loud (race core), and number of discs makes no real difference to db with a race core, I have trouble keeping it under 100db which is our limit....usually get it on 97db for the test. The noise is harsh and almost buzzy at high rpm, but performance is better all round than the stock set up - I've played around with the Supertrapp a fair bit, currently running 10 discs and 2'' end cap...with 6 discs and 38mm end cap it's pretty close to stock....but louder.

[Houseoffubar]

Originally Posted by Sabre170

Thanks! I really appreciate.

I really like the looks and sound of the exhaust in the second link you posted. The R100 with the "shorty" megaphones. I, thinking that will likely be exactly what I'm looking for.

Do you know off hand what size header pipes my '78 100/7 would have on it? I'm out of town for the next week and can't measure my bike. I want to say that the muffler would need to fit a 38mm manifold pipe, but 40mm and 42mm are also rattling around in my brain as possibilities.

38mm or 1 1/2"

[supershaft]

Originally Posted by bmweuro

If you can weld we have a guy locally that builds a kit for BMW's and has for over 20 years. Probably the only one that does not rob power. Here is his contact info. http://www.facebook.com/pages/Hanson...26407367414973

His 2/1 is on this bike http://www.teamincomplete.com/Boxer/boxerhome.html

Unless your rev range is around 1500rpm or less, all pipes without variable volume via valves and plenums and whatnot, no matter the type, are going to rob power. The question is where in the rev range and how much. That is simply a fact of physics.

[bmweuro]

Originally Posted by supershaft

Unless your rev range is around 1500rpm or less, all pipes without variable volume via valves and plenums and whatnot, no matter the type, are going to rob power. The question is where in the rev range and how much. That is simply a fact of physics.

I've built 2/1's that made power from 1800 RPM to through red line. It is very do-able and yes it is all math from pipe length, collector length and diameter.......

[Airhead Wrangler]

Houseoffubar made me this



...out of pieces from these guys: http://www.coneeng.com/

[RGregor]

The 2-1 exhausts from SR-racing are quite popular over here in Germany.

http://www.sr-racing.de/anlagen/BMW/R100GS.jpg

No one has ever complained about performance, in fact they give a rather significant boost over the complete rpm range.
However, I would not use them if classic looks were important.

Regarding the second crossover tube of the post '81 models: I have a technical article where the authors (engineers from zeuna staerker, the company that developed and manufactured the BMW exhausts then) describe the effect of the crossovers as follows:
- The first crossover improves low-mid rpm torque
- The second crossover improves mid-top rpm torque.

My dyno runs have shown this exactly.

[Airhead Wrangler]

Originally Posted by RGregor

The 2-1 exhausts from SR-racing are quite popular over here in Germany.

http://www.sr-racing.de/anlagen/BMW/R100GS.jpg

If I'm not mistaken I think SR racing also make siebenrock's exhaust systems don't they?

[Prutser]

Originally Posted by Airhead Wrangler

If I'm not mistaken I think SR racing also make siebenrock's exhaust systems don't they?

You are right AW its the same as the siebenrock system.

The system is not a big improvement on a stock 800 engine. The bike will loose bottom torque.
But with some engine tuning the system starts to work.

[DiabloADV]

Originally Posted by Airhead Wrangler

Houseoffubar made me this



...out of pieces from these guys: http://www.coneeng.com/

I'm in the process of copying that setup. Keep getting sidetracked on the honey-do list...

[RGregor]

Originally Posted by Prutser

You are right AW its the same as the siebenrock system.

The system is not a big improvement on a stock 800 engine. The bike will loose bottom torque.
But with some engine tuning the system starts to work.

I admit I don't know anyone with a stock R80.
I even think I don't know anyone with any stock engine ...

The Siebenrock exhausts are built from SR. Which does not necessarily mean they are the same.
From SR-racing you normally get full service, which means they "build" the exhaust on your bike and tune the bike on the dyno afterwards. And they have a variety of different mufflers to fit.
A couple of friends have these exhausts on their bikes with positive reports.

[supershaft]

It seems everyone is comparing the SR pipes to the stock setup. That I am not interseted in. Almost any setup is going to cost you some bottom end power over the stock setup with a stock engine. What would be intersting is to hear how they compare to other types of aftermarket setups. As far as welding up my own two into one setup for my bike? There are just too many variables and I don't have the dyno and the time to figure out collector shape and length. How far down the pipes does the collector work best, etc.. I could surely copy some that I hear work real well over other aftermarket setups. Personally, I think I am going to stick to two into two's just for tuning simplicity. Plus I have decided that I am not going to go looking for TOO much more through the exhaust because I know from experience that the big gains are going to be LOUD and I am now too old for LOUD. That and now there are a million Harely's out there and almost all of them are LOUD. I don't want to be a part of it.

[RGregor]

Originally Posted by supershaft

It seems everyone is comparing the SR pipes to the stock setup. That I am not interseted in. Almost any setup is going to cost you some bottom end power over the stock setup with a stock engine.

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.

Originally Posted by supershaft

What would be intersting is to hear how they compare to other types of aftermarket setups.

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.

[bmweuro]

Originally Posted by supershaft

It seems everyone is comparing the SR pipes to the stock setup. That I am not interseted in. Almost any setup is going to cost you some bottom end power over the stock setup with a stock engine. What would be intersting is to hear how they compare to other types of aftermarket setups. As far as welding up my own two into one setup for my bike? There are just too many variables and I don't have the dyno and the time to figure out collector shape and length. How far down the pipes does the collector work best, etc.. I could surely copy some that I hear work real well over other aftermarket setups. Personally, I think I am going to stick to two into two's just for tuning simplicity. Plus I have decided that I am not going to go looking for TOO much more through the exhaust because I know from experience that the big gains are going to be LOUD and I am now too old for LOUD. That and now there are a million Harely's out there and almost all of them are LOUD. I don't want to be a part of it.

Why are you commenting on this thread? No disrespect just curious.

[chasbmw]

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.

I like the idea of a stealth bike......a BMW that looks almost stock, but goes much better than people expect

[chasbmw]

Originally Posted by RGregor

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.

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?