Re: Technical question: VANOS

["Allan Williams" <allanw@xxxxxxxxxx>]

If it ain't broke, don't fix it :-)

BMW's Vanos is to boost low rpm torque... that's why the *peak* figures
don't really change. The engine has a *LOT* more low down torque.

Honda uses the technology to turn a high revving gutless motor, with a VERY
high power figure, and insane RPM levels into a drivable motor. The Vtec
makes it much more drivable - it has to be more complicated to bring the
powerband back down the rpm range. If it was to run it it's "high rpm" stage
all the time, it would be a complete pig to drive. If it was to run in it's
"low rpm" stage, it wouldn't rev high, or produce the peak power levels it
can.*** You can also look at it the other way - it turns a drivable motor
into a performance motor. The engine was designed to reach high peaks to
start with though.

Peak power is NOT a good thing to tell performance from. My Holden company
car only has about 65KW peak, where the Hyundai Lantra loaner (while my car
is serviced) has about 85KW. The Hyundai is much slower even though it is
the same weight. The Hyundai is far too peaky, but then runs out of power as
the revs rise too high. The band which the power comes on is about 4.5K to
6K. In my Holden it is 3K to 6.5K.

Hondas system doesn't have extra cams, it has extra lobes on the current
cams, and an extra set of followers which are actuated hydraulically at
certain rpm stages. It alters valve lift and timing. The ecomony version of
VTEC (VTEC-E) sometimes only opens 3 valves all the way to get great
economy, while it changes at higher rpms to creat a little more power.

Vanos and Vtec acheive two different objectives. A broad torque curve, and a
high peak power level.

Allan :-)

- ----- Original Message -----
From: Michael Ting <lupin@domain.elided>
To: BMW Digest <bmw-digest@domain.elided>
Sent: Wednesday, August 16, 2000 5:09 PM
Subject: Technical question: VANOS


I was reading about variable valve timing technology. (credit to AutoZine)

First, there is Honda's cam changing VTEC. Then, there is BMW's cam phasing
VANOS.

I think it's safe to assume that VTEC costs more to implement than VANOS.
(multiple cams, as opposed to changing angles)
It's also clear that VTEC offers higher performance gains. The closest
example that I could think of, is E36 325s. Can I say zero performance
gain??

So my question is:
Why does BMW, being an advanced engine manufacturer, uses the cheaper, lower
performance gain technology? (surely price is not a big concern in BMW
engines)
Or why not implement something that uses both valve changing and valve
phasing? (like new Celica GTS' VVTL-i)

To add the confusion, sports cars like Ferrari's 360 Modena, and Diablo SV
is also said to use VANOS like, cam phasing technology. (Not sure on this
one)

The only answer that I can come up with is that smaller displacement is more
crucial in Japan. thus they're willing to put in the $$$ to research these
technological tricks.

Maybe someone can come up with a better explanation.


Michael Ting
- --------------------
Learning the theories behind my wonderful bimmer. :)












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