A little more on port matching - what Jack found working on the flow
bench is that if you open up the intake runner ID too quickly you
kill the flow through the manifold. The air delaminates from the
surface and becomes turbulent. You need to keep the change in ID to
under 7 degrees of taper. Also, look at the port in the head - some
of them had a ball mill shoved in for a short distance and the inner
port diameter is much smaller. In that case you may be better off
adding epoxy to the port in the head to make it more of a straight shot.
He also found that a step from smaller diameter to larger diameter in
the direction of flow wasn't very harmful to overall flow.
http://www.tonydrews.com/uncle_jacks_engine_building_tips.htm#Head
Tony Drews
At 04:06 PM 10/8/2014, John Styduhar wrote:
>You should read what Kas has to say in his prep manual.. He recommends
>port matching.
>
>On Wed, Oct 8, 2014 at 3:57 PM, Dan Cronin <adcronin@mi.rr.com> wrote:
>
> > 10/8
> > Thanks to all who took the time to read my query and respond. Very
> > interesting variety of thought on wether or not matching the ports is a big
> > deal --- or not (as long as the gas / exhaust flows from smaller to larger
> > bores).
> > Dan
> >
> > On Oct 7, 2014, at 3:46 PM, Dan <adcronin@gmail.com> wrote:
> >
> > I am preparing my TR4a head to accept the intake and exhaust manifolds and
> > there seems to be a rather significant difference in the diameters between
> > the
> > intake ports of the head (1-1/2" dia.) and the intake manifold (1-3/8 to
> > 1-7/16" dia.). In addition, the two mating gaskets I measured come in with
> > a
> > dia. of 1-23/32nd, just under 1-3/4". The literature I have consulted
> > recommends that the intake ports of the head and the manifold match up
> > perfectly including the dia. of the mating gaskets. Not so critical on the
> > exhaust as a "notch" to the upside on the exhaust port apparently aids in
> > extracting gases. What have you all found in your engine building
> > experiences? I could carefully enlarge the intake ports to match the head,
> > but the remaining intake (TR4a long runner) shell would need to be a
> > opened
> > up around 7/32nds thereby perhaps weakening the runners? Thoughts?
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