[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]

Re: TT in T.O.

Wolff writes:
> I read an artical about the 4 valve vs. 5 valve heads. More isn't always
> better. It comes down to whether the stroke is long or the motor is
> "over square". The Audi motors typically have smaller bores and longer
> strokes for good torque making the 4 valve a better choice. I don't
> recall the specifics, but that's the gist. A short stroke motor with
> wide pistons makes better use of the 5 valve technology. There is more
> space around the plug for valves.
> Wolff

You got it backwards... The article in question was in European Car.
It said that the 5-valve design works particularly well with long
stroke motors for street use.

This can be observed by comparing the VW 1.8 16V engine (like those found
on the late 80s Scirocco II) versus the Audi 1.8 5-valve unit (non-turbo
version, which we don't get in the U.S., but is found on some Euro Audi A3s
and A4s).  The two engines have identical bore and stroke.  The Audi has a
lot better torque characteristics, as well as having slightly better
high-end horsepower.  Some of this can probably be attributed to improved
fuel and spark management in the Audi, because it's a new Motronic-based
system rather than the VW's old KE-Jetronic, but I believe the lion's
share of the difference can be attributed to the 5-valve head.

The VW 2.0 16V used on the later VWs can barely match the Audi 1.8 5V
non-turbo in horsepower, and still can't match it in its torque curve,
despite the increased displacement.  Or look at it this way, that extra
valve is worth more than 200cc in the 4-cylinder!

96 A4 2.8 quattro
84 5000S 2.1 turbo
80 4000 2.0
    ///  Ti Kan                Vorsprung durch Technik
   ///   AMB Research Laboratories, Sunnyvale, CA. USA
  ///    ti@amb.org
 //////  http://sunsite.unc.edu/tkan/