Re: Engine design question

[aspeer@mail.utexas.edu (Andrew J. Speer)]

I think this was discussed a few months back, so you might want to check the
archives.  Audi decided on a 2 valve engine (after manufacturing DOHC 4
valve I5s for quite some time) for a little known, but very good reason: 2
valve engines produce better torque in the low to mid rpm range where a
driver spends over 90% (with the exception of several q listers) of his
time.  A flat torque curve is far more important for everyday driving than
top-end power.  A 4 valve engine breathes better at higher rpms and can thus
generate more power, but at the expense of decreased low-end torque (ever
driven an Acura? you'll know what I mean).  Make no mistakes about it, the
Audi 2.8 is a sophisticated little mill.  It sports a variable intake
manifold (interesting article in this month's EC) and the latest
Bosch-Motronic fuel management system.  Come springtime the 2.8 engine gains
a new 5 valve head, and variable intake timing to solve the
lack-of-low-end-power conundrum.  Even so, power increases to 193 not 300 so
you haven't missed out on that much unless you live for skirting that rev
limiter.


Andrew Speer.