anesthes wrote:
.........Now the wrench thrown into this mix is forced induction. I'm running between 6-8psi of boost. My camshaft has 2* of overlap at .050".

So I think we can throw out any sort of scavaging since the intake is pressurized.........
-- Joe

LT4BUD wrote:
The main point in selecting headers isn't really flow.....in fact it is scavaging....

CentralCoaster wrote:
Matching up the flow bench numbers implies you care about having the same amount of pressure drop across the valves as across the primary tubes.

I don't see any reason to try matching those values. Maybe it'd be more worthwhile to match velocity. None of your parts are going to flow that cfm on the car anyways.

Personally I'll take the least restrictive part available anywhere I can get it on the system until there is a penalty in torque loss or something.

CentralCoaster wrote:
Leaning towards it.

But even with forced induction, you still have pressure waves bouncing back and forth through the primaries, so it seems like they could still provide scavenging.

But maybe the smaller pipes required to accomplish that do more harm than good on a blown motor, I don't know.

tequilaboy wrote:
Not directly on topic, but here's an interesting read on overlap and scavenging with inlet pressure greater than exhaust pressure. (I love these old NACA reports):

http://www.not2fast.com/NACA/naca-tn-405.pdf

and another (more interesting):

http://www.not2fast.com/NACA/naca-tn-2025.pdf

tequilaboy wrote:
I know there are some ceramic coated impellers intended to improve efficiency mostly used for turbos. I don't know how effective they really are for centrifugal superchargers, though. Less friction with the air maybe, I think the Raptor uses one.

Coating the volute/diffuser may keep the components themselves cooler, but I think that would just tend to increase the charge air temperature.

I'd really like to see somebody do a fully shrouded impeller like the old DVL design. That's supposed to be the most efficient impeller style. Basically an impeller with a cover on top of the vanes which avoids any leakage between the vanes and the case. Would be expensive.

CentralCoaster wrote:
400f reduction?

Um, are they implying that it's 500 degrees in there right now?

CentralCoaster wrote:
Looks like some attempt at an equal length setup, which is overrated on the already imbalanced timing of each cylinder bank on a 90* V8.

jhammons01 wrote:
The reason that there is no data on FI over N/A is that forced induction will have no effect on CFM at all.

CFM will be dictated by the smallest orifice in the entire setup......once you've determined where the smallest orifice is.....and you calculate the flow of said orifice, no upstream pressure will change that flow.

So you are looking for Data that does not exist and that is why you are asking it on this forum....what I mean by that is you are a very very capable researcher.....and you are failing to find what you are looking for, hence the need to ask here.

jhammons01 wrote:
"tuned" I am not an expert but the way Tuning of intakes and Exhaust were explained to me was the "Flow" or waves are tuned to move at the right time. Picture a wave in the ocean hitting a wall or a jetty. The wave "bounces" back creating a wave heading in the wrong direction.....you want that wave to hit the other side and be heading toward the inlet valve when the valve opens up again.....that is the reason for the "Length" of the plenum being so important.

jhammons01 wrote:
Headers are the same way, there is a restriction, somewhere down there, a valve opens up and exhaust comes flying out of a chamber in a large wave...you don't want that wave to hit the restriction and come flying back just at the time the valve opens up.....

That was the explanation I got on flow and tuning.

The CFM part I work with every day and I am sure of those facts. The Tuning part.....I'm just throwing things out there

anesthes wrote:
I put a lot of weight in both of their opinions.

CFM will be dictated by the smallest orifice in the entire setup......once you've determined where the smallest orifice is.....and you calculate the flow of said orifice, no upstream pressure will change that flow.

Reprinted from page 99 of Scientific Foundations of Vacuum Technique by Saul Dushman 2nd edition (J.J. Laffery - editor) with permission from John Wiley & Sons. Copyright © 1962 by John Wiley & Sons.

Adopting some general rules, Dushman's results can be applied to tubes of other cross-sections. The results will not be totally accurate, but, since the calculated conductances are likely underestimated, it is often worthwhile to use them.

* For tubes with right-angle bends, measure 'L' as the shortest distance shown.


Calculate the conductance from the table as if the tube were straight, then divide the conductance by 2 for every right-angle bend.
* For tubes with rectangular or square cross-section (or even the annulus between two tubes), calculate the open area and find the radius of a cylindrical tube with an equal open area. Calculate the conductance of this 'equivalent tube' using Dushman's table.
* If the diameter changes along the length of the tube, use the smallest diameter to calculate 'a'.

Conductance Conclusions

When designing a vacuum system or changing components in an existing one, always attempt to maximize conductance. In any high-vacuum situation, keep these points in mind:

* It is all too easy to lower conductance accidentally.
* Make all tubes and components as short as possible and as open (with large diameters) as possible.
* The part with the smallest conductance determines the maximum conductance.
* In high-vacuum or UHV applications, the concept of the conductance being too high has no meaning. The converse, however -- a conductance 'too low' -- happens all too frequently.