Sfc Exhaust
- Thread starter Lavermax
- Start date
TeddyG
Hero member
- Location
- Portland Oregon
My understanding is that a mid pipe helps the mid range, and I believe that cross over is SFC specific for dual exhausts- do you have that or just the 2 into 1 megaphone?
Tippie
Hero member
- Location
- Dr?bak, Norway
It allows both "mufflers" to exhaust both cylinders, thereby also far more quiet than the open 2 into 1. Also as stated it may help with mid range, however my experience with high comp SFC motors for racing is that they have more than enough mid range even with 6C cam. It also makes the system far more stable and unlikely to crack than two independent systems. This system would have been great on the big valve SF models instead of the ground clearance reducing but very efficient collector they have.
motoddrob
Hero member
- Location
- S/W Australia
Having both systems for my SFC, I'd say if you want performance use the 2/1. If you want to ride on the road without scaring the shit out of people use the 2/2. The 2/2 makes the SFC run like a well tuned SF1-3 where as the 2/1 makes the SFC run like it should.
MarnixSFC
Hero member
Not much I can add to that other than that it is the silencers that restrict the 2 into 2 system. Late drum brake SFCs came with a very similar collector with a pair of megaphones which work very well too. These megaphones had long cones which made the system less noisy.
Marnix
Marnix
Dellortoman
Hero member
- Location
- Tasmania, Australia
Buongiorno Lavermax. How does it help mid-range power I hear you ask? Allowing the exhaust gas to exit via both mufflers reduces back pressure at the exhaust port over a wide range of engine speeds which allows the engine to better scavenge the exhaust gases so it can suck in more fuel mixture on the next inlet stroke. The exhaust gas pulses come at different times for each cylinder. When one side has a pressure pulse the other side is doing nothing, so it may as well be put to use to help get rid of the exhaust gas.
A high performance 2-1 with megaphone works in a different way. It's a resonant system that works really well at one engine speed (when you want max power) but not particularly well at other engine speeds. Hence the poor mid-range.
Just a bit of idle speculation (not being a 750 afficionado). It seems apparent that they chose the X pattern for the crossover rather than a simple 90° T-connection because the 45° take-off provides an easier path for the exhaust gases to divert into the other side.
My 1976 Guzzi LeMans has a balance pipe with a crossover at 90° to the headers. I doubt it does much balancing. I'd guess only about 20% of the exhaust gas actually manages to turn the sharp corner and go into the other muffler.
A high performance 2-1 with megaphone works in a different way. It's a resonant system that works really well at one engine speed (when you want max power) but not particularly well at other engine speeds. Hence the poor mid-range.
Just a bit of idle speculation (not being a 750 afficionado). It seems apparent that they chose the X pattern for the crossover rather than a simple 90° T-connection because the 45° take-off provides an easier path for the exhaust gases to divert into the other side.
My 1976 Guzzi LeMans has a balance pipe with a crossover at 90° to the headers. I doubt it does much balancing. I'd guess only about 20% of the exhaust gas actually manages to turn the sharp corner and go into the other muffler.