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kenikh kenikh is offline
3 restos WIP = psycho
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Join Date: Feb 2005
Location: North of Exit 17
Posts: 7,729
To dovetail off of your point on technology allowing deletion of previously necessary parts like the cams in diesels, BMWs latest turbos really are showing the future wave today. These cars have NO throttle bodies. Yep, that restrictive and disruptive bottlneck to clean airflow into the motor hase been deleted since BMW can now control all air metering AT THE INTAKE VALVE with their dual VANOS cam system. The benefits of this range of adjustability trickes down into all performance aspects of the motor.

IIRC, with this system, lift is a function of a dynamic actuator which is not directly dependent upon the camshaft itself. The camshaft becomes nothing more than a dumb valve actuator and gross parameter controller. With lift of the grind isolated from the power curve, it only imparts profile shape as a baseline curve, manipulated at the valve through a multiplier relationship with the lift mechanism. It becomes a simple reference component for mechanical lift potential and for mechanical energy transfer into a dynamic system. The camshaft is thus primarily supporting only the lobe spacing control in direct relation to the area of the base cam lobe profile when it comes to volumetric efficiency at a given RPM.

With this system, the cam can lift fast and low (assisted by the low reciprocating weight of 4 valve heads), easing mechanical wear and decreasing frictional losses to levels impossible to achieve just 2 years ago. As a side benefit, more power is transmitted to the driveline. More importantly, as overlap and lift are now computer driven parameters, an engine's behavior can be (within a range) dynamically tailored to suit high BMEP low in the RPM band to make big torque and instant boost response, then open things up on rev increase to allow big power production through scavenging and lift.

It's like having a nearly infinitely sliding performance scale that marries part of the efficiency of a 2 stroke, the off idle torque of an RV cam and the peak power of a 935 cam on the fly, on demand. This valvetrain trickery is the reason whay a 3.5L inline 6 in a new Bimmer can hit full boost by 1500 RPM and hold pressure to redline with a table flat torque curve the entire way. Where in the past, to get that low a boost threshold, you'd need a turbo that was too small to support the top end or a strangling cam, you can now trick a big turbo to act small, where you need it.

I only hope that one day the aftermarket will get the trickle down from the big boys, so us dinosaurs with air cooled motors can reap the benefits. With all of the advances we've discussed, if they'd been available in 1995, I think that we'd still be seeing air cooled 911s on showroom floors today. Porsche is not far behind BMW, so hopefully we'll see more soon in our favorite marque.

Good fun, eh?

- 1965 911
- 1969 911S
- 1980 911SC Targa
- 1979 930

Last edited by kenikh; 06-11-2010 at 10:31 AM..
Old 06-11-2010, 10:27 AM
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