Copy the Nismo XR6 Turbo intake. Turbos run more intake volume. It's about 3.0 litres, has 1.5" runners, about 4 " long, with a 2.5 liter tube which is regarded as a yunkky piece of crap by the sceptics. Who cares? Theres 1500 hp to be had using it and a turbo!
I'll coment on what I've found on this subject.
The working principles are complex, as there is a whole bunch of air flow figures on the net called harmonics. Most books and websites natter on and on about 2nd, 3rd, 4th and 5 th order harmonics, and then baffle you with figures which 'can't do nothing for ya man'.
The best thing I've got is plenumb volume from the Grand Master of Big block Sixes,
Frenchtown Flyer.
1) He says that the volume of the plenumb is important. 30to 60% of the engine capacity. As an example, the XE to EA/EB multipoints have 2.3 liters capacity, and runners of about 10 to 12 inches (250 to 300 mm). The port sizes are 1.4" for the early XE to XF's, then a little bigger for the EA/EB.
2) Turbo XF guys often run 6.5 to 7.0 liter intakes, which works great for boost and mid range power, but poor for low end response and hi-end power. That's 160% of the engines capacity!
3) Second, your bang on over the intake runner length. Over the history of the motor car, there are rules which tend to show 5 to 7 inches is the ideal intkae runner length if you have space to package it. If you don't, then go for shorter and bigger runners with upstream throttle slides, and the injectors have to sit quite close to the valve, 4.5" is optimum. With single or dual throttle body intakes, ( all modern EFI'S use single runners for ease of service, although they trade off a lot of power over an isolated runner carb set-up. HSV Group A's were dual throttle body in race form), they run up to 12 to 18" runners to get bag loades of low end torque.
4) Throttle body. Six is best on a six. Port on port in the Charger 265 six pack style is still the ideal. If you have to use a single, then make sure it floes air. Ford Explorer V6's had a range of diameters, and the bigger ones were worse thann the smaller ones for air flow. Rule is generally to ensure peak air speed isn't too high. 150 to 200 feet per second at 1.5" Hg is the critical speed. If your big 4.0 revs to 5500 rpm, then it needs about 330 cfm of air.
If it has, say, a 62 mm throttle body, and revs to 5500 rpm, then the air speed at wide open throttle is only 168 feet per second. The idea is that a biiger throttle body will kill air speed, and make calibration harder. If you make it too small, it changes the stability of the wake of air down streem of the throttle body.
Summary
Volume, (total excluding intake runners) 30 to 60% of capacity, non turbo, 70 to 160% of capacity as a turbo
Runner length, 4" minimum, 6 to 7" ideal, 12" for low end torque,
runner diameter should be intake port diameter
ideal format is six upper slide throttles, but its expensive and hard to calibrate, so most of us use a throttle body that is smooth and large, and gives the 150 to 200 feet per second speed at peak rpm.
Hope that helps.
Now read up on Bowland and Grippos page from the Ford Six tech section
http://www.bgsoflex.com/intakeln.html
Then do a
search with Injection Intake Manifold Design
I got about 10 pages plus from 83,300 selections. Man, I hope ya
love reading!
