Ok boys.
I have read all the posts on siamesing the base.
Went to the shop and measured the runner length on my old
single plane intake I had on my 70 Chevelle.

That engine dyno'd at 365hp and had plenty of midrange power
and pulled to 6500rpm. I think it had a genuine Chevy 350/350
cam in it, single pattern .447 lift, 221 duration and 114 centers.
Anyway the ports in it are alot shorter (from head to plenum)
than the tpi base ports are from head to runner.

So, if I cut like 2" into the tpi base, the runners will still be longer
than my old single plane manifold so it should still make good
low/mid range torque and run up to 6000rpm or more.

My question is.
With the base siamesed, and each port drawing from 2 runners,
wouldn't the volume of the combined stock runners, which are
now acting as extra plenum area negate the need for large tube
runners?

 

I think so. In theory, you are doubling the stock area, although in a running condition you are losing some of that especially the 5 and 7 since they fire one after another. Its still a fair amount more than the stock runners though.