I fitted a new pattern 4-4 exhaust to my Z900A4 last summer and found that it was way too loud (in my opinion), i.e. much louder than any standard exhaust I remember from my younger days. I initially thought this was due to a faulty baffle and the pipe in question was replaced by the supplier. The new pipe is a bit quieter but it still seems too loud.
The general perception is that the pattern systems are constructed in the style of the original Z1 with removable baffles, unlike the KHI genuine pipes which are the more restrictive (and quieter) 1976 version.
Well, after a bit of investigation with an endoscope (ooh err missus!) I have concluded that this is not true and that the pattern pipes have the later 1976 internals but have the original 1973 design baffles fitted. The upshot of this is that there is even less restriction than the original design. See the diagram below (sorry for the file size and the poor drawings).
In each case the gas enters from the left and exits on the right.
Fig 1 shows a standard Z1 exhaust.
Exhaust gas passes from A into the baffle pipe until it meets the blank mid-way along B, it then enters chamber B where some passes back into the baffle beyond the blank and some goes via the balance pipe to chamber B of the associated exhaust. The wadding and small holes in the baffle at chamber C are only to absorb sound (like the induction silencer on Z900A4 air filter), no gas passes into chamber C.
Fig 2 shows a standard Z900A4 exhaust and apart from the shape, this system is completely different from the original Z1.
As the baffle pipe blank is located at the extreme LHS all exhaust gas passes via a tube from A directly to C, the gas then turns 180 degrees and passes through another tube from C into B. At this point the gas splits with some entering the baffle tube to exit and some passing via the balance pipe to B of the associated exhaust.
Fig 3 shows (my) pattern exhaust (1976 construction with 1973 baffle)
If you look at this you will see that the gas can get out just about anyway it chooses!! No wonder it seems loud.
Am I right?
Am I the only one to have come across this?
The bike looks good and runs great - “ better than with the previous 4-1 system
I'm still researching this at the moment so don't leave your pride and joy where I may stumble across it as I never leave the house without a gas-axe and a petrol driven angle grinder!
What's the solution?
It would appear that without much effort I could adapt the baffle or blank off the inner pipework to achieve either of the original designs although I'd like to think the manufacturers should address the issue (no chance).
I could live with it - “ most likely.
Any thoughts?
Andy
