Scott....is there a particular reason you went with that manifold? I had been asked about going in that direction (turbo manifold with individual throttle bodies) and, while technologically impressive....decided that it was too overly complex, difficult to tune and heavy for what it ultimately needed to achieve comparative to other designs. Have you found an advantage to exploit with that style of manifold?
First up, apologies for the lengthy reply. If it needs to be moved from this thread, then please do so.
I chose this manifold for a few reasons.
Now I'm not a fluid dynamic specialist, but I have a very basic grasp of basic air flow characteristics from back at uni.
The plenum is designed to give even flow to each runner. It's not all that visible in the pic, but the plenum itself is actually angled towards the last cylinder. The taper of the plenum with the angle of the POE (point of entry), is such that it doesn't favour any particular runner. The radius of the plenum profile in the base of the plenum is such that it should eliminate or significantly reduce low pressure turbulence caused by sharp edged corners. This reduces low pressure turbulence under the POE.
Each runner is curved towards the POE. The runner closest to the POE has a greater curve than the last runner. Each runner also has a nicely radius-ed entry with a tapered out leading edge. This reduces low pressure turbulence around the entrance of each runner.
The throttle plates are of significant sizing in comparison to the standard TB. 40mm per runner in comparison to 40mm and 46mm. Each 40mm plate has a surface area of 1256mm2 (3.14 x [20 x 20]). This multiplied by 4 gives us a total plate area of 5024mm2 or that equivalent to an 80mm TB. The standard TB gives us a combined surface area of 2917mm2. This does not take into account for TB shaft diameters. The quad throttle bodies run a 10mm TB shaft.
Every body is aware of the high torque (at low rpm) nature of our engines. There is a lot of discussion that the head and the long stroke is the cause for this. However, long (380mm stock) and narrow (30mm - [I will need to confirm this]) gives high torque lower in the rev range. My idea with going for ITBS and shorter (200mm) and larger diameter (40mm tapered) runners is to try to increase the gas velocity above 3500rpm to shift the torque curve higher in the rev range.
Having ITBS should
give better throttle response in comparison to a single 80mm TB as each cylinder will receive the same amount of air once the throttle is cracked. I'm also not concerned about significant loss of torque/power in the lower end of the rev range, as I have got some counter measures for low end power. This is another topic for discussion, but it has to do with cam selection (and operation), head work and turbo selection.
There are things about the manifold that I am not happy with. POE diameter and port angle post throttle plate. The entry is 2.75". I am wanting to run 3" intercooler piping so this will need to be changed to 3". The port angles post plate should be rectified by doing a cut and shut between the ITBS and an F2 head flange. Going by measurements, I should be able to get a pretty straight port once completed.
I understand the concerns in regards to tuning, but this is not really an issue. The standard RNN14 manifold has individual vacuum ports on each runner. These are connected to a common vacuum chamber to which all vacuum/boost lines can be tapped. A MAP sensor will be used along with a TPS. This will give me enough control over idle and light throttle tuning. Having this common chamber effectively makes tuning the same as it would be with a traditional manifold.
As I'm not building the car for a specific class rule, or have a very low target weight, I am not that concerned over the weight of the manifold. The car will have a complete interior and I am considering reinstalling a/c. however I'm hoping the weight will be comparable to standard manifold.