the new s4; motor notes

[Dave Eaton <dave.eaton@minedu.govt.nz>]

1st sorry about the post with the unedited reply.  a few years on the list, and
i reckon that was my first goof-up.  thanks also for the lack of flames...

jst some notes about the new s4 motor which may be of interest...

1) the reason for the sleeve down was to ensure the reliability of the head
gasket at the 9.3:1 cr.  wouldn't work with 2.8 litres of displacement (the
bore went from 82.5mm to 81.0mm) apparently.

2) exhaust temperatures were also a major issue.  with this in mind the
manifold consists of a narrow pipe inside the manifold itself.  there is an air
space between the narrow inner tube and the outer manifold skin.  the double
skinned approach helps under bonnet temperatures and also ensures that exhaust
gas temperatures and velocities are good (brings to mind a thread...)

3) the drive-by-wire throttle is lifted from the tdi.

4) throttle response was a design criteria.  shortened exhause to turbo
lengths, smaller turbo's and drive-by-wire were all aimed at improving throttle
response.

5) the amount of overlap allowed by the valve timing is 22 degrees.  the
camshafts are different from the normal 2.8l v6.  the camshaft arrangement is
the usual 5v head design with cambelt driving the exhaust camshaft with this
linked to the inlet by chain (through the variocam tensioner) at the rear of
the head.

6) there are no variable length inlet tracts.  the twin intercoolers look to be
quite small but are supposed to reduce inlet gas temperatures by 70-80 celsius
at full power, which isn't too shabby.

7) the torque curve is very impressive with 250nm @1,000rpm, rising to 400nm
@2,000 and staying at this level until just below 4,000rpm.  the curve almost
exactly mirrors the rs'2 except that it occurs 500rpm lower in the rev range,
and the rs2 looks to breathe better at higher rpm's (bigger turbo), so that the
rs2 maintains higher torque from 3,500rpm.  but at low rpm, the s4 is
exceptional.  at 1,500rpm, it is pulling 310nm (!), while the 20v quattro is at
235nm, the rs2 is pullng 209nm and the sport quattro 180nm.  at 2,000 rpm, it
is 400nm vs 309 (ur-q 20v), 250nm (rs2) and 205nm for the sport. very very
impressive.

8) the power curve is not quite as impressive, although again the s4 is
producing more power than (in order) the 20v quattro, the rs2 and the sport
before 2,500rpm.  at 2,500 the rs2's power curve crosses the s4's and the
sport's crosses the 20v quattros.  thereafter until 4,000rpm the rs2 and s4's
power curves are pretty much identical.  after 4,000rpm, the s4's tails off and
the sport's gradually rises to be near the rs2's.  the rs2 and sport's bigger
turbo's and higher lift cams would account for this difference.

an intersting motor.  i'm hopeful of having a test drive by the end of the
month (according to the sales-type droid).

dave
'95 rs2
'90 ur-q