The stock bore on a Porsche 944 Throttle Body is roughly 55mm, which is fine for stock power (250HP on the Turbo S), but when it comes to building more power, we have no choice but to flow more air. Interesting enough, the opening of the stock intake manifold plenum is much closer to 65mm (obviously this is a 10mm difference). Now that might not sound like much... but 55mm vs 65mm is actually a percent difference of nearly 17%, which we think is a significant enough amount of potential airflow to look for an opportunity in redesign.
Our plan is to bore out as many millimeters of aluminum (our friends across the pond would call that "aluminium") as possible from the stock throttle body without affecting the integrity of the part.
Now we could just mount the original Porsche part on our CNC mill or CNC lathe, grab a boring bar and keep cutting until we destroy the body (all in the name of research), but before that we figured we could/should/would reverse-engineer the part using a good set of calipers, micrometers, and our trusty Computer Aided Design (CAD) software.
Once we have that modeled, then it's just a matter of using the integrated CAD tools to really determine the maximum bore possible... but that's not as much fun.
So here's the plan... we will reverse-engineer the part, determine the maximum bore theoretically, 3D print a few prototypes that we can use to setup the CNC machine(s), destroy our 3D prints taking the bore to beyond the max, and finally, perfectly machining the stock Porsche throttle body to the safest maximum diameter.
Let's begin!
Part 1 - Measurement and CAD
Computer Aided Design models are only as good as the data going into them. This good data comes from good measurement. And good measurement comes from good equipment. We grabbed our trusty micrometers and calipers and went to work. The second challenge with CAD is what is the "best" way to make the part. And by best, we mean efficiently and accurately. In the case of the throttle body, we started by defining the overall geometric shape (and in this case, that shape was oddly familiar to a warp pipe from Super Mario Bros...).
Following the fundamental shapes, we then begin to add the supplemental shapes, often using the original geometry to establish reference geometries.
And finally, after about 2 more hours of going back and forth between taking measurements and designing the CAD features we have a completed (albeit virtual) Porsche 944 throttle body.
And for confirmation... we measure the bore in CAD (55.5mm)
In Part 2 we begin to virtually dissect the throttle body and see just how much material we can remove before really compromising the part...
Stayed tuned!
E