Airhead R100GS Y-Pipe Performance Change?

[rwiles]

I've heard that replacing the exhaust collector box with a Y-pipe changes the power characteristics; moves the powerband up and reduces low-end torque.

Izzat right? Anyone have any experience with putting a Y-pipe on and Airhead GS?

[SOLO LOBO]

Rob Farmer has a thread with dyno charts... use the search feature...

[Rob Farmer]

I fitted one. Spent a small fortune on dyno time trying to sort it out before buying a standard collector box.

The keihin Y piece just doesn't work properly but there are European options that are reported to work very well. Obviously I have no idea what you guys have in the states

This ones on Redboots R100GS PD




Sold by Motoren Israel --> http://www.motoren-israel.com/produc...t--EG-ABE.html

My Dyno tuner was very scathing about the Keihin. The design meant the gasses from each cylnder were constantly being interupted by the other cylinder. The only way I could get it to run well was to drop the needle a notch to weaken the mixture. This actually increased the power but nowhere near as much as fitting a standard collector box.

Food for thought - HPN, Andrew Sexton and a few other reputable BMW tuners all keep the standard collector boxes.


I contacted Keihan about the issues with their collector and asked if they would produce a standard style collector box in stainless steel. this is the reply


"In the last few months we have re-designed our y pieces due to customer comments like yourself, this has made them free'r flowing so improving the performance.

We have no plans at present to reproduce the collector box.

Regards
Mark Regan"

Apart from the issue with the Y piece Keihan are a great company to deal with. I haven't tried their newer style collector.

[impi]

I had one fitted to my R100PD when the original collector rusted out. A good Y-pipe will be balanced (In other words, the total distance the gasses travel from the header to the junction in the Y will be equal for both cylinders - thus when looking at the Y-Pipe, the left cylinder section will normally curve inward and then out again before meeting up at the junction. If not you run in to issues.

The same principle also applies to the collector boxes. If you cut one open you'll see that the left pipe has a section that extends into the collector box before it dumps the gasses.

My personal observation of fitting the Y-pipe at the time was that there was marginal degradation at the low end. Nothing earth shattering - it's an airhead afterall. The bikes sounded more like a wet fart than anything else and the topend didn't really change (maybe seat of the pants). The driver for the Y-pipe install was more cost driven than anything else.

I lived in NZ at the time and the pipe I fitted was made by a local firm. (BMP or something like that).

[Rucksta]

I have an NZ copy of the G/S Muffler made by Muscat or some other variation of the spelling of Musket. I picked it up second hand in Aus and it hasn't rusted out in the 5 years I've been using it.
I was told they make a replica collector box.

No idea where in N.Z they are but you N.Z. guys may be able to find them and let me know please as I'm due for a new collector box. R80G/S type

[Rucksta]

Originally Posted by BOETJE

Here you go :

http://www.musket.co.nz/index.asp

Ugly though...

Thank you .
Looks like no junction box available but an effective looking "Y" pipe if there is such a thing. At least this one makes a good attempt at equal length.

The muffler doesn't look any uglier than the original. The finish at the rear where the muffler body meets the tailpipe is a bit rough but an orbit with the grinder & flat black paint hides it pretty well.

[motu]

I made a 2 into 1 for my R65 Mono - unequal length into an IDSII Supertrapp.Works perfectly - but it's only an R65,nothing sophisticated like an R100GS.....

[Stagehand]

Damn.

When I fitted mine it was a cost consideration, as well as a weight thing. My original collector was so shot full of holes I'm sure I never noticed a reduction in low or mid power.
That collector is such a big hunk of metal it pains me to consider putting one back on.

found a couple good deals on Ebay, though.

[C Squared]

http://www.japmcdismantlers.co.nz/

Check out these guys.

I bought a "tuned" 2-1 collector fron them a few years back and then grafted a ISDA Supertrap from a TE 610 onto it. I like it but I have no Dyno info.

It looks to be hydro formed and then welded.
It is for the GS.
I cut and re welded a joint and use it on my R100R.

Worth a look as is looks to be equal length rather than a Y

I made a phone call from WI (USA) to NZ and maybe a week later I was holding the pipe. They also do replacement mufflers.

[igormortis]

Hmm, those look like the same pics as from the other place.

[C Squared]

Originally Posted by igormortis

Hmm, those look like the same pics as from the other place.

Sure does.

Both in NZ so I am sure that they are the same.

I like mine

I have never seen another like it.
Mine is on a 92 R100R.

[Stagehand]

The Keihan was the only option besides that Epco epic, or the roll your own, back when...

Damn your eyes, New Zealand parts guys! Where were you when I had rusty collector bits 5 years ago! I'd almost pay a hundred bucks to get my bottom end I forgot I was missing back, AND get that cool ass twirly gig under the bike. I supposed it can be Chromed?

[Phreaky Phil]

I tried on of the Musket Y sections on my R80 a few years ago. Mid range went west. It feels like it just revs through the range without any punch. On an R80 you need all the oomph you can get !! Its now collecting dust in my shed.

[bpeckm]

A 38mm diameter pipe has a cross section of 1134 mm.

A 40mm diameter pipe has a cross section of 1256 mm - an increase of 11%

To have the full 2x diameter of the 38mm pipe would require a 54mm diameter pipe. But, assuming that there really is no need for a full 2x (after all, the pipes fire back and forth, with the exhaust pulses going out "evenly spaced"), something bigger than the 38mm would be helpful, certainly.

38mm is roughly an 1-1/2" pipe
54mm is roughly a 2-1/8" pipe

I have a fairly crudely-made 2 into one on my R100, and it does go into a 2" pipe which is welded to the muffler. Works fine, though I have not had it "compared" in any way to stock, so I don't know if it adversely affects performance... or not...!

[Stagehand]

I gotta go to new zealand.