Exhaust diameters

["Stefano Iachella" <iachella@xxxxxxxxxxxxx>]

Hey Cats,

Anyone well versed in exhaust diameters and their 
effect on HP, torque, etc?

Kartalamakis' book says optimal diameter out of
when the secondaries come together is 52 mm, or
about 2 ". The guy who did custom secondaries for
me on the Shankle Alfetta exhaust made them
come together to a 3" collector because my hollowed
out Cat was 3 ". My power/torque is virtually non-
existent below 3000 rpm.

I'm about to have him put a new cat on and was thinking
of reducing the diameter back down to 2 or 2.5 " to
get the back pressure back and shift my power curve
down a bit for daily driving. It screams at 6000 rpm.

Is this the correct approach? 

Other pertinent info:

79 Alfetta
74 engine (cams + Spica)
K&N filters.
Stock center resonator and muffler

Thanks,

Stefano
Oakland, CA

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