twist wrote:this is really sort of new to me, the science of exhaust tuning. If I understand what I've read so far, the longer pipes are actually better for performance. Why is that?
Generally speaking, header diameter, primary length, and collector length
will affect torque delivery, torque peak, and peak HP.
It's always a balancing act.
Torque that comes on quickly and reaches peak output at usable road RPMs
are certainly desirable traits for a general purpose
street bike.
Smaller diameters and longer lengths will do that.
Sport-bike tuning will often sacrifice that tractor-like torque delivery
for a bit more HP at the top and greater top end speed.
Exhaust system design may need to be different to attain
those characteristics.
Performance is not an objective entity –
The term MUST be defined before qualitative terms like "better" can be applied !
The bottom line ?
The "best" exhaust system design will provide
the most useful power curve –
this will be different for every application
and must be defined by (the specific needs of) the individual.
twist wrote:It would seem that getting the exhaust out as fast as possible would allow the intake to flow better, too.
Exhaust theory is quite complex and not nearly as simple as all that.
A good intro article from
Burns Stainless
twist wrote:...what good does wrapping the headers do ...
Wrapping causes steel headers to rust in short order.
The theory will be that wrapping retains heat within the header
and therefor increases velocity through the system.
Originally wrapping was used in racing autos to keep header heat
from affecting other components under the hood.
twist wrote:... how much cooling do those finned nuts actually provide? Would using a header nut without fins really make that much difference?
Apparently enough to justify the extra expense of a complex machined casting !
But then, the style was just so very fashionable back in the day ...
i.e.finned exhaust nuts are no longer used, even by BMW.