charles.harbert wrote:

Paul (Yaw), could you be a little more specific as to what you didn't

like about

the short 20B manifold ("crap" too generic). A friend of mine built it

and I've

looked at it closely. The only way to meet the space available (5" wide)

was to

construct it as a combination IR and small plenum inlet using 1/8" flat
aluminum.  It may look crude from the outside, but the inside is blended

and

smoothed with no square corners. Actually, the outside isn't bad.

Are you objecting to the flow paths, or the quality of construction, or

the

runner lengths, or .....? I agree that the air must make some abrupt

direction

changes which are not good for high rpm efficiency, but the space

constraints

caused this. Would the small plenums inside the manifold help overcome

the

change in direction?

Finally, you said that you can build tuned length manifolds, but it is a

trial

and error process which to me means it's pretty expensive. I was talking

to Bob

Darrah and he's trying to keep the cost of the manifold under $500,

whereas to

build a tuned manifold (incl testing) is probably well over $1,000. What

would

be your estimation of the difference in hp between a short maifold and a

tuned

manifold running between 4-6,000 rpm? Thx.

p.s. Really enjoyed your money tech articles.

Todd Carrico wrote:

I am not speaking for Paul Yaw, but I can tell you what I don't like about
it.

The runners are different lengths.  This will cause small differences in the
volume that makes it to the chamber.

Fuel will tend to seperate from the air in the tights turns.  More
differences in the Mixture in each cylinder.

So, now we may have a situation where the mixtures and volumes may differ.
If the Pair of runners that run into each chamber match for volume, and the
turns are the same length they may cancel and give you reasonably matched
charges.  I am deffinatly no expert here, just exercising what I think to be
common sense.

Back in the day, short runners were for high RPM, and the long runners were
for lower RPM., also larger plenums tended to be for higher RPM.  These are
for V8's not for Rotary's, but it seems to apply here as well.

Now, If you are going to Turbo, it may not be an issue.  A little boost can
go a long way toward fixing any bad flow issues <grin>.

tc

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