Variable Restrictiveness Exhaust

[Gary Derian]

I don't really know how these mufflers work.  I think the Mitsubishi had a
vacuum valve that blocked part of the muffler's outlet.  This changed the
tuning and made it quieter.  According to this month's Car and Driver, the
Maxima has a spring loaded valve that opens up at some set backpressure.
There is no active control.

Gary Derian <gderian at oh.verio.com>


> 1)
> Gary,
> can you elaborate on how that muffler varies?
>
>
> Gary Derian wrote:
> >
> > Adding backpressure just for the sake of it won't improve low speed
torque.
> > Having small diameter ports which happen to add backpressure will.  Its
not
> > the backpressure that improves torque.  Its the low rpm tuned components
> > that do.  Now, having a variable restrictor that quiets the car when
> > cruising is a good idea.  The new Nissan Maxima has such a muffler.
> > Mitsubishi 3000's have had them in the past.
> >