I've been off the board for a long time, but this post caught my interest. Back in 2002 I tried port EFI on a stock 250 (no turbocharging). Made a custom manifold to hold the injectors, etc. Sure it ran, but there were always dead spots in the range where it would falter. Examination of the exhaust ports and manifold, plus the plugs led to the conclusion that #1 and #6 were running lean. At the time I wasn't thinking about valve timing, but more intake manifold geometry and was it ramming more air in to 1 and 6...

Anyway, to try something different I went to a TBI on a 4-bbl Offy manifold and that cleaned it right up!

This always puzzled me, and a few years back I found this link:
http://www.starchak.ca/efi/siamese.htm
which explains why the whole problem of charge robbing occurs. Makes so much sense when you look at it, and I wish I'd found this back in 2002.

So, given this reality, I think the only options (untried by me) are the "port divider" proposed above, or perhaps the clifford manifold for the three side-draught webers. I wanted to try three small TBIs, mounted on their sides and flowing directly to the head. At the least, this should provide a few even air/fuel distribution, because the geometry of each siamese pair will be identical.

Greg

1977 Chevy C10 SWB
EFI 292
SM465