Exhaust balance pipe - vital?

I scored a pair of shiny chrome-ridden NOS exhausts for the Ural form
ebay, see. Slightly different part number, but looked pretty much the
same and the old ones were deffo shagged to the point of being beyond
redemption.

The question is - is a balance pipe vital? The old exhaust has a pipe
connecting the two 'silencers' and the new one has no such provision.
How desperate is an ancient design of low-powered flat twin, copied
from a 1940's BMW for balance of exhaust pulses? I can't imagine it
would affect power output too badly if the cylinder scavenging was not
100% ... or would it?

Anybody got a clue? Anybody GAF?

Perhaps I ought to nosh the tow headers together into a bean-can
collector and ram them into a spare old Bandit can stuck on the
outside, survivor-bike stylee.

 

However, I do know from PPC mag, that collectors are a) difficult to make
and b) design is quite critical. Can't remember the specifics but IIRC the
angle that the pipes meet at affects power delivery.

 

On a Urinal? No way.

(When I remade the exhausts for my Z400 twin, I disposed of the balance
pipe. And the earlier models didn't have them anyway).

 

Hmm, well ISTR Platy's Eastern Bloc Crapster ran okay with one of the
pipes hanging off where it joined the head. The comedy bubble machine
noise was quite amusing too.

--
Dan L

Too much time to think, too little to do.


http://thebikeshed.spaces.live.com/

2002 Triumph Sprint RS 955i (It's big, and it's black)
1996 Kawasaki ZR1100 Zephyr (Gone, but not forgotten)

BOTAFOT #140 (KotL 2005/6/7/8)
X-FOT#000
DIAABTCOD #26
BOMB#18 (slow)
OMF#11

 

I'd say not - the Guzzi had balance pipes as OE but the Conti type open
megas it has now don't.

I'm led to believe they smooth out the pulses and have a quietening
effect. It's been said on a twin they clear the gasses quicker but I'm
not sure about that.

 

I can sort of see that: ignoring pulse reflections etc then each
cylinder has in effect two silencers at its disposal.

 

That's how it was explained to me.

 

Would you like a small stack of "Horizontal View" (OC mag)?
--
Jeweller
R100RT
Formerly: James Captain, A10, C15, B25, Dnepr M16 solo,
R80/7, R100RT (green!)
www.davidhowardjeweller.co.uk

 

How to configure the exhaust system on a twin is an oft visited topic on
the Morini list. 2:2 with balance pipe, 2:1, or 2:2 without balance
pipe.

All have been tried. The 'official' racing system was a 2:2 without
balance pipe. Those that have experimented with that say it is crap (on
the road at least). 2:1 requires matched header lengths before the join
or they can make setting up the carbs very tricky. Given the 72 degree V
with ports akimbo this makes for convoluted plumbing. For best all round
results 2:2 with balance gets the votes. Though Morini took great
trouble on OEM systems to run the rear pot pipe way up inside the
silencer to give matched header lengths as well as using a balance pipe.

On a flat twin, the pipe lengths are hardly an issue. So a balance pipe
is certainly not vital IMO, though as Sweller said it might be a tad
noisier.
--
+----------------------------------------------------------------+
| Pete Fisher at Home: |
| Voxan Roadster Gilera Nordwest * 2 Yamaha WR250Z |
| Gilera GFR * 2 Moto Morini 2C/375 Morini 350 "Forgotten Error" |
+----------------------------------------------------------------+

 

Thanks very much for all that, Pete. Noise won't be an issue, as the
guts of the old pipes fell out when stood upright - so the new ones
have /got/ to be quieter of themselves (even though there is an
audible tinkling of Russian rust and debris inside them already).

 

After the Dnepr shed a pipe - and it ran perfectly well all the way home, if
a little noisily - I seriously contemplated doing a 2-1 on it. The pipes
would have run down either side to meet up behind the sump, then off to the
left to connect to an old car back box between the bike and the chair. This
would have looked fine and minimal, but it ended up a lot easier just giving
my hard-earned to Mick Cross and slinging new ones on:

http://www.facebook.com/photo.php?pid=119185&l=3f49b&id=528363400

These had no link pipes or anything, but the performance - if I may describe
it as such - didn't seem to be affected.

 

Catching up with this late... as it is an old BMW lump it will be just
fine without the cross pipe! you will be able to set up the
carbs/tickover quite nicely.