Intake Runner Length

[Tony Bryant]

Bruce says:

> 
> I worked at an R+D shop, and for a while Ollie Morris (one of the great of
> manifold designers), and find Smokey Yunick's quote of "square ain't as bad
> as
> it seems" (or words to that effect) meaningful.  While many ports look like
> beautiful
> sculptures, sometimes it's just better to take you licks, and be done with
> it.
> Specially with a dry manifold.  Considering at 6,000 rpm from butterfly to
> intake valve the "air" is only in the intake for like .008 (and possibly
> much lesss) of a sec. it ain't there long enough to estabish boundry
> layers/laminar flow enough to matter (for other than all out race
> applications).  Worry about the bowl, and valve,
> the most.   Specialy if were still talking about a turbo VW.  Then we can
> get to keeping the total valve diameters not to exceed 85% of the bore, or
> shrouding
> gets to be an issue (non-hemi heads)..  Sir Harry Ricardo, just realised I
> hadn't mentioned him in two weeks.
> Cheers

Speaking of shrouding issues, I've just finished porting a head for 
my EFI Datsun L20B (2 valve non crossflow head).

I made a cylinder sized pedestal extension for my flow bench, to 
attempt to simulate the shrouding effect of the cylinder walls (I have 
a 92% combined valve dia/bore ratio). 

To my amazement the flow went up as compared to the vastly 
unrealistic unshrouded situation I had before that. A quick 
investigation with the 'flow direction and velocity indicator' (a piece 
of sewing cotton tied to some welding wire), revealed that the flow 
patterns had changed from being concentrated on the ceiling, to 
being concentrated on the outside wall of the port, with the flow 
curling around the valve stem . 

I found the optimum port shape changed significantly. A completely 
different approach needed to be taken, than in my previous setup.

I had always heard and read about how ports set low in the head 
don't flow worth a damn, but now I'm not so sure; my small low 
rectangular exhaust ports almost outflow my high, round smooth 
intakes! 

I also have a theory that low intake ports add significant swirl to the 
incoming mixture, for very little cost in flow.

My 2c