If you're worried about abnormal eddy currents/turbulance in a manifold with ~13 90* bends (combined) connected to a 4-cycle motor in which the valves pop open in a rather oddball sequence, I'd say you're more than just ****. IIRC it takes a good 2 feet before gas will return to somewhat laminar airflow. You're far from breaking the camel's back with tight or uneven runners.

One other thing to note, your 'recirculating areas' (your overhanging turbo flange & runner inlets that are slightly larger than the exhaust ports) actually are included in many professional motor builds, as it actually helps exhaust keep moving out. If you look it up, there are several similar patents that work this way to increase exhaust gas scavenging and reduce/prevent reversion. That little-known theory behind the venturi effect is one way to understand the method behind that madness (I'm talking efficiency tradeoffs here).


All that aside, I'd go with better transitions/collectors/design/etc over equal-length any time. In many cases, the odd turns required to make a Honda turbo manifold truely equal-length means adding lots of restriction just from the turns alone. True they aren't all 90* bends, which usually create a pressure drop of 3-4x that of a 45* bend, but its how the overall runner snakes around.

In any case, unequal length divided manifolds with tight bends will smoke any undivided equal-length work of art any day of the week.

 

I believe Holset has some info for you on their website, or maybe Bullseye regarding B-W turbos. IIRC You don't do it with vacuum, rather you spin the turbo to create the intended shaft speed & pressure, then measure delta-T and overall flow. Effective efficiency readings are tough because you basicly have to measure ALL temp changes (air, iron), and seperate what came from the shaft. That's why I think many turbo makers don't have good flow maps - because they are very difficult to get, accurately.

Double-posts normally aren't my thing, but I wanted to keep this seperate.

 

That's how it generally works (pretty good HiProfile). Each manufacturer has a couple of other calculations they put into account that they won't let me release (silly, but I gotta keep a job).

To the OP: if you're thinking 20cfm is just "an additional 20cfm is better than not", then I'm afraid you're going to be spending more time underneath the car than driving it. 20cfm can be easily made up in your exhaust system catalytic converter or an air filter or something small and easy to replace.

Its the difference b/w in the office calculating and on the street with the actual application.

 

Considering that I shift <4k RPMs during daily driving, and I don't make boost until >4k, the head helps a lot. When I swap on a stocker every 2 years to pass smog, I cringe at the loss of low end torque. I don't regret the head work at all, and I'd gladly pay to do it again.

 

you said you "radically" ported your head ? if that's the case your car must suffer from idle to 3500rpm. do you have any flowbench numbers

 

This thread has run its course.

 

I'm sure it has. Good luck with whatever your ultimate goal realistically is.