I finally got a chance to check the 2->1 shown above on a dyno. To do it, I had to venture into the heart of darkness...
Very nice folks, actually! We decided I should swap my worn 908 for a scorpion for the dyno, they came out to watch me change the tire and were bug-eyed when I pulled off a sub 10 minute swap in the cold. I got a private chuckle out of that, not sure how often they see that from their dentist crowd...
Into the war room:
Pull the pin and stand back:
I tested the bike 3 ways. Everything else, jetting, tire pressure, etc, remained the same otherwise.
1) 2 into 1, neptune exhaust, baffle out.
2) 2 into 1, neptune exhaust, baffle in.
3) 2 into 2, neptune exhausts, baffles in.
I would have liked to test more variations, but this ain't free.
Pictures speak louder than words:
The answer is a resounding hell-yeah. Peak horsepower was made with the 2 into 1 installed, baffle out, and the 2 into 2 and 2 into 1 with baffle(s) in were within 6/10ths of a hp peak.
There are some additional changes in character that are more important, in my opinion.
First, the 2 into 1 options seemed to perform better below 5k RPM, with somewhere between 1 and 4 more pound feet of torque. From the saddle, this feels apparent, with a smoother bottom than stock, somewhere that is commonly useful.
Second, the 2 into 2 option really only has an advantage from about 5 to 7k RPM, where it in turn makes 1-4 more lb/ft. This is the "hit" that is apparent from the saddle on the stock bike, which is considerably smoothed by the 2 into 1, not only because of the minor loss in this area but also because it's stronger below, so the gains present are less apparent.
On pavement, the 5k hit is fun to "surf", but in the dirt, IMO, the more linear the power the better, as it makes it easier to retain connection with the rear tire. The bike still has plenty of go at these revs, to sacrifice a few pound feet up here in exchange for a smooth characteristic is a worthy tradeoff, again IMO.
On top (7k up), there isn't much between them. Baffled vs. baffled, they are very close. Unbaffled 2 into 1 beats them both, and I suspect unbaffled 2 into 2 would equal or beat that. Anyway, I don't ride there much, so that it's within a few is all that's important to me.
Jetting was as we ran it in Baja (too rich) and was not changed between the 3 pulls.
So, the power of this system is arguably better than stock, depending on what you're looking for, but the biggest advantage to me is the weight loss. Stock cans weigh 11 lbs EACH, up high, and as far from center of mass as possible. Aftermarket cans vary between about 5 lbs and about 9 lbs. A 2 into 1 system loses that weight instantly, as well as freeing space for a tank, a map tube, whatever.
I was impressed enough with this outcome to think there's a product here, hence my posting in Vendors. I spoke to some buddies that run a racecar shop, and they turned me on to a fabricator who can produce these. I sent him the prototype, and finally got a quote back for a low production volume, which I need to decide whether to give the go ahead on.
The offering would be a 2 into 1 that looks exactly like this:
This will fit any muffler that bolts to the stock "H" pipe, including stock of course. It will use all stock mounting points.
The piece for sale would not made from pieces of a stocker, obviously.
Instead of the crappy chroming of stock, this would be jet-hot
coated, which will never blue, is easy to clean, promotes good flow characteristics, and so forth. The price would be $225 shipped in the US.
Some changes will have to be made to fit an adventure, I haven't tested these yet but they would be on top of my list to do. There would be an offering for both SE and ADV owners in any case. The SM is different, so no love there.
If you're interested and/or have questions, please let me know either with a post here, or a PM, or an email from my profile. I intend to make a decision fairly quickly, and once I do, the pieces would be 6-8 weeks out, so still in time for riding season.