Ace Bristol racing spec.

[Lee]

Note that a "tuned" exhaust normally suggests equal length runners from each cylinder to the collector.
   
   THe AC "LeMans" exhaust is configured like the street version, ie the outer cylinders have longer tubes than the inner ones prior to the downtubes.  It is not tuned in the classic sense.
   
   I've never actually seen a tuned header on a Bristol motor, and would be really interested in a pic if someone has one.
   
   Lee

[pls01]

We're confusing equal length and "tuned" exhaust.
   
   Equal length is just as described; all the runners are equal length.  For practical purposes, the LeMans exhaust is equal length as the runners are with 4% of each other. In essentially straight pipe, this length difference creates negligble difference in flow resistance.
   
   Tuned exhaust was the holy grail of engine builders.  The idea was to built exhaust gas velocity and momentum down stream to help scavenge the cylinders.  If it worked at all, it was only good at the tuned engine speed.  Lower speeds did not produce the scavenging effect and higher speeds just produced more flow resistance.
   
   The period racing exhaust could more accurately be decribed as "practically equal length, possibly tuned LeMans exhaust"