are there general purpose aluminum filler rods that i can use
blindly? an old standby? or is aluminum too sensitive?

The most universal Al filler is probably 4043. While there are
better
for some jobs, that's the "do anything reasonably well" alloy.
Ernie
says 4047 is better for castings. I plan to get some to try but I
have
had success with 4043 even if it isn't the best.

Ted




4047 has twice the silicon content of 4043, so it has better wetting,
a
lower melting point and less weld shrinkage.

How about welding plate to cast? I want to take a V6 cast aluminum
intake manifold, machine off the original plenum and runners leaving the
water passages, valley cover, and about an inch of the intake runners
coming off each flange, and then make my own plenum and runners from
something like 6061 sheet about 1/8-3/16" thick for the runners and 3/16
or 1/4" for the plenum to handle 30 psi boost, and then weld my runners
to the cast stubs. Sort of a cheap way to get a short runner large
plenum single plane sheet metal intake manifold without spending $2500
or making up all my own flanges and jigs. I am guessing the manifold is
something like A356, because I've read it's most common for automotive
head and manifold castings. Is this weldable? What alloys would y'all
recommend?

--
Regards,
Carl Ijames