> and add a port-and-polish.
Be careful with that, Brian. I've heard many times now that it's easy to
actually make things worse in that department, if you don't know exactly
what you are doing. Polishing in particular can actually increase
resistance to flow and lead to drivability problems, because the "as cast"
surface creates a boundary layer that eases air flow, while fuel tends to
stick to the polished surface.
Randall
Indeed. I performed the combustion chamber work per Kastner's book. For
the ports, I was guided by Uncle Jack, who shared with me the work that
can be done reliably, without a flow bench, for most of the gain, and
steered clear of the great deal of effort required for any subsequent
benefit.
For inlets, you remove the two main cast-in obstructions and then leave
the reshaped surfaces rough. This roughness aids fuel atomisation and
creates a layer of stable air close to that surface that then eases gas
flow through the port. For exhaust ports, the advice is to smooth the
short side of the throat and then polish all surfaces to inhibit carbon
buildup.
I have the early TR4 short log-like inlet manifold. Passing through this,
gasses are required to navigate two 90 degree corners, with sharp edges
and dead spaces. It is improved by rounding corners as much as the
material allows, but being sure not to widen the 'bore'. One can read of
gasket matching, or better, port matching, however Uncle Jack advised
against this and I left the manifold ports alone. One area I did find for
obvious improvement was the fitting of the insulating gasket to the
carburettor. I marked the orientation of my insulating gaskets and put
stud-diameter pegs in the carb's plate in place of the studs and then
fitted the gaskets to the carburettors only. Both gaskets were off centre
with respect to each carburettor. I had the same result with respect to
the manifold, with gasket 'intruding' maybe a quarter-inch into the throat
of the inlet. A few minutes with a dremel on the insulator removed this
obstruction.
Brian
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