Hello, I've owned my 75 850 mkIII since 1976 and I've always had the stock black cap mufflers on. What is the advantge, if any, running the pea shooter type mufflers with out the crossover pipe by the head?Thanks for any input.
Hi Christian, I would think the advantage of the "pea shooters" is they are straight-thru pipes. So I had the adventure, on a Sunday morning ride my right peashooter muffler just fell off! By the time I realized this, turned around and rode back there was my muffler, squashed like a beer can (sheared the mounts by the rear footpeg).
So when I got replacement pipes (Dunstall copies) I noticed you could look right through the peashooter (no wonder they were louder). It is my understanding that reduction in exhaust back-pressure allows the engine (otherwise known as "air pump") to be more efficient; i.e. the more air you can get thru the cylinder head, the more power you make
I have run most combinations of silencer and down pipe on my Mk III 850 Nortons always said that the "Black-Caps" only work properly with balance pipes. 850 Mk I and II (Not "A") had balance pipes with the reverse cone "pea shooters" and it works OK.
The biggest difference is one of noise. I don't find the Reverse Cones too loud if the revs are kept down in built-up areas but they are definitely louder. They are less prone to rot and the Black Caps now available are not as per the original "Annular Discharge Silencer" internally. I have not used the current type.
My impression is that the Reverse Cones make the pick up seem crisper and let the motor breath more easily plus sounding fantastic on the over-run. Balance pipes seem to help the low to mid range torque but again, it's just my impression and they are more trouble to fit and more likely to fracture than unbalanced pipes.
I have finally settled on Reverse Cone silencers, Non balanced pipes and a 750 airbox, ie precisely as a late 750 and it is the set-up that I like best.
When I bought my 850 Mk 2A new in '74 it had the black cap silencers and balance pipe . I soon changed to pea shooters . when the time came to change the header pipes ( after one crack too many ) I also pondered over the use of the balance pipe . I went to the trouble to make an air valve in my old balance pipe that I could operate from the handlebar with a choke lever . So , riding at different constant speeds , I opened and closed the balance pipe . If there was any advantage in power or torque I Should feel the bike accelerate or decelerate . I felt NO difference at all ! So , no more balance pipe for me . I still have that balance pipe with air valve lying arround , so if someone cares to repeat that test , he can have it .