WATER HAMMER MANIFOLD TUNING 2

[BillyShope]

I have some questions concerning the computer modeling of engine performance. I might have been the first, back in the fifties, to realize that runner length tuning of engine manifolding did not involve acoustic waves (which, by definition, involve negligible pressure differences), as proposed by Phillip Smith and others, but was merely an example of that phenomenon, usually associated only with liquid flow, known as "water hammer." Petroleum engineers, for instance, have long known the importance of the scheduling of valve closure to avoid the very high pressures which can result from the slight compressibility of a liquid. I found that the water hammer equations, when applied to the automobile engine flow conditions, could easily provide the pressures needed for the observed torque changes.

Further, I found that the empirical NL = 84000 equation, developed at Chrysler in the fifties, could, with the addition of terms to accomodate the "harmonics" and changes in intake duration, reliably predict all the little torque curve "bumps" associated with tuned intake manifolds.

I left the industry long before these sophisticated engine performance prediction programs were developed and I'm now wondering how they "handle" the tuned intake manifold. It would appear to be no small programing job, since, I would think, multiple internal "clocks" would be needed to keep track of the pressure fronts. I had a short conversation with a programer at Chrysler, who assured me that everything was taken into account, but I'm not totally convinced he understood exactly that to which I was referring. Anybody out there have any experience along these lines?

 

[dynodan]

Billy,
You might want to talk with the guys at

http://www.optimum-power.com/,

or Prof. Gordon Blair at

http://www.profblairandassociates.com/

they are very knowledgable regarding engine simulation.

Regards,
Dan