As you noted before, anything compared to the sorry-excuse-for-an-intake-manifold-design as the stock TDI one is, would be an improvement. The stock manifold has absolutely NO runner length whatsoever and a plenum (if you want to call it that) volume that's barely half of the engine's swept displacement.
VW apparently gave zero regard to tuning (which is reasonable for a forced induction diesel motor), but instead arrived at a design that would package well and be the cheapest to manufacture and use the absolute least amount of aluminum that would resemble an intake manifold
I would be interested in learning more about the calculations you did, Jake. I am quite familiar with the Helmholz method to determine resonant frequencies, but I've never done a hand calculation before. I have created a bunch of engine analysis and calculation spreadsheets over the years; I'd be willing to share them and I'd also like to develop one for the manifold design as well if it hasn't already been done.
I have developed a couple excel spreadsheets... one for testing the real-world validity of the organ-pipe tuning formulas using the racing jaguar intake manifold study data I found in a book as the test (you can see the results for yourself), and another that does the organ pipe tuning equations to calculate tuned frequencies of the various reflective values for a given motor for various intake runner lengths. They are both sort of quick and dirty but you will probably be able to figure them out.
The main piece of data you need to know for a motor to make use of the organ-pipe tuning equations is the intake camshaft duration. I have that info for the 1.6lD/TD motor, I'd bet it is similar for a TDI, but if you know it that's even better.
I will see how I can get these spreadsheets to you... E-mail would be easiest, but maybe there's a way I can get them up on the net (too bad I am out of server space...), let me think about that. Also to accompany the jag tuned freuqency spreadsheet, I will try and scan in the VE vs RPM plots of the racing jag motor from the book.
Jake, the reduction in VE due to extremely long runner intakes is due to the boundary layer flow loses due to the surface roughness. That's why, as you noted, much more has to be considered when tuning than just one parameter, such as resonant frequencies.
It should be noted that the plastic upper intake manifold has a smoother surface finish than any aluminum casting.
I just got done reading my new book, "Scientific Design of Intake and Exhaust systems" (1972, but amazingly the points it makes explain a great bit of modern engine design!) Quite the in-depth read.
The author rigged up cool apparatus that was capable of reading pressures inside cylinders, exhaust manifolds, and intake manifolds as it changed over fractional rotations of the crankshaft movement during engine running. It explains a lot of very interesting things.
Anyway, I now have a definitive answer as to why too long of an intake runner saps high speed power. What happens with a long intake runner is, early in the intake stroke, as the piston moves down, airflow is lazy with the long runner, due to it's long length and high mass of air, it resists movement initially, and there is a build-up of vacuum inside the cylinder. This build up of vacuum causes the rate of airflow through the intake runner to increase to very rapid rates, and that airflow given enough time (low enough engine RPM) overtakes the expansion of the chamber related from the speed of the piston, and if it has enough time before intake valve closes, can even "supercharge" the cylinder. At high rpms however with too long and narrower runners, the delayed filling of the cylinder during the intake stroke doesn't have enough time to "catch up" with the vacuum generated inside the cylinder at the early part of the stroke.
There was mention that this effect could be reduced by porting: enlarging the diameter of the hole behind the intake valve and the rest of the length of the runner behind.
Makes perfect sense to me
[Furiously taking notes for book title]
Also a great (but not light) read is
Turbocharging the Internal Combustion Engine by Watson & Janota.
hey ! i think there is a good book in english! do you know where i can buy this book?
yep! i go to amazon then i will receve : Scientific Design of Intake and Exhaust systems,
but the other is not dispo