gotzoom? wrote:Did you waterjet the flange on the itb manifold side? How did you arrive at the
tube length of the adapter manifold?

There wasn't a lot of science involved

I made a simple CAD drawing and had
both the flanges waterjet cut. Then I used aluminum scaffold tube, which I calculated
to have the right diameter to match the intake ports when squashed down. Put a curve
in it with a pipe bender which partially collapsed the tube into almost the exact port
shape. Cut the U-bends in half, then a bit of massaging in a press and good enough.
The length was pure chance... I just needed them to be long enough clear some of
the stuff on the intake side on a RHD car, and tilt the throttles up a bit. Due to some
brain fade at the time of welding up, the TPS ended up in front instead of at the back,
as I had intended. But happily, that mistake actually working in my favour... space is
awful tight at the rear of the head.
I did look at the calculations for tuning the intake tract for a particular rpm. But came
to the conclusion that when the engine is required to work over a wide range of speeds
and space is limited, the harmonics you are trying to catch are not significant. If you
have the room you can experiment with stack lengths. I have finished up with very
short stacks, and they work well. Probably because I have more inlet runner length.
Cheers... jondee86