variable exhaust?

[pounsfos]

they are on most new cars

honda uses them
toyota uses them
some motorbike have them
some mitsibushi's use them (vaguly recalling this one i could be wrong)
it mainly an emissions device but it does increase fuel economy

as for how much i don't know

[nemesis]

Originally Posted by Allch Chcar

Sonic Velocity is why headers are wrapped and Mass Velocity is why tubing is sized, right?

From my weak knowledge, the diameter of the tubing determines the torque range based on the engine configuration.

I can't help with the variable exhaust but I do know of a variable intake design.
Ford uses a second set of throttle bodies in their engines to improve the low end air velocity for better low end torque. I've personally seen them in the 3.8 liter V6 in the Ford Windstar where they were located one in each intake just before the fuel injectors. But I know they also used them in the Ford Ranger at some point. The switch to full open was in the 2k-3k RPM range.

Sorry that I can't be of any help.

I own a mustang with a 3.8 lol, know all about this variable intake set up

[gone-ot]

...presently, you find more INTAKE systems using "tuning" techniques than EXHAUST systesms, mostly due to the HEAT problems, but it *is* possible.

...a "mechanical" example of EXHAUST tuning are the 2-stroke muffers which are specifically designed to certain engine speeds--raise the low-end torque and high-end power at an acceptable loss of mid-range.