1976 Z1000 A1 exhaust measurements

[Henley19]

Can anyone help please? I am having a new set of pipes made, 4 into 2 and the engineer has asked if I can obtain some measurements? 1 - Downpipe width, he assumes inch and a half, correct? 2 - circumference of box small end and then circumference at the large tail end, 3 - distance from where downpipe joins box to tail end of box. Does this make some kind of sense? Any help would be appreciated

[Mick J]

It's a deep subject. I suggest you obtain a copy of " Four Stroke Performance Tuning" by A. Graham Bell. It explains the way the dimensions of an exhaust system can have a profound effect on the power and torque characteristics of an engine. As a rule of thumb, keep the downpipe lengths close to standard, make the angles of the collectors ( where the downpipes converge into the secondaries ) a shallow angle, there is an optimum, which I can't recall at the moment, and make sure that the cross sectional area of the secondary pipes is a least the same size as the area of two downpipes, preferably slightly larger, for a four-into-two. Inch and a half downpipes sounds about right, I wouldn't go smaller, like the Delkevic, I believe has smaller downpipes, which hurts gas flow. Make sure to use mandrel bends for proper flow, as there is no change in area of the pipe. Hope this is of some help, regards, Mick

[zed1015]

Go for 1.5 inch down pipes at close to 27 inch long.
That's the proven dimension that works best on these motors regardless of tune.
After that, unless you went for 4 into 1 for best scavenging the 4 -2 configuration doesn't really aid performance especially if joining in 1-2 and 3-4 configuration so just avoid going smaller than downpipe diameter after the 2-1 merge collectors.