David Stauffacher wrote:
> And while the carb TR6 has a nice sound to it, the PI TR6 has a distinct bark
> that puts people on notice that you are packing a 150 horses beneath the
> bonnet!
And Bernard Robbins wrote:
> One of the things I love about lucas injected
> cars is the bellow of the induction noise which is more pronounced.....
The "extra" sound of the Triumph PI cars relative to the Federal carb cars
is not due to the induction sound of the PI; that sound you hear is the
lumpier cam speaking.
There are three ways you can simply change (and tune) the sound your engine
generates (I'm ignoring the use of isolative materials):
- exhaust path
- induction path
- cam timing
I could go on for pages on this, but not now.
The PI with the standard air-intake path (the whole path from the air
cleaner up by the radiator, along the hose into the tubular chamber by the
injectors) acts like a still-air box in modern cars. Induction noise is the
sound made by an acoustic wave that is generated when the air mass is
suddenly halted by the closed valve (as well as all the turbulence caused
along the path). Some of this energy in this collision is converted to
sound. This acoustic pulse is then reflected back through the incoming air
mass and because of the relatively short induction path used by carbs
relative to PI, less signal is attenuated. With the long induction path of
the stock PI system this acoustic wave attenuates more, especially the
lower-frequency components. Ergo sum, the PI has less induction noise.
You can test this yourself. If you have carbs, take off the air cleaner and
listen to the sound it makes, especially above 4,000rpm. You will hear
significantly more high-frequency signal (which is normally attenuated by
the air-cleaner box). Bolt on velocity stacks and you will really wake up
the neighbours - that9s why they call them "trumpets", Mate! That9s right,
velocity stacks act like a megaphone.
Do the same with your PI cars; unbolt the tubular collector; you will be in
for a treat.
The reason why modern cars have still-air boxes is to silence the induction
roar, which in a trumpeted system, can be as loud as an un-muffled exhaust.
Still-air boxes are one of the few areas car designers can really control
sound levels cheaply and effectively.
Shane Ingate in Maryland
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