I have a 2 carb intake on my 270 with a small port head. I am looking for better top end performance.
I had larger valves installed, some porting and smoothed transition / alignment rings when putting the big port intake on the small port head.
I get good low end response and it pulls good until about 4000 rpm when it starts gasping for air (or at least that is what I think the problem is)
I put smaller venturies in the Zenith carbs at the outset because I figured it would be too much carburation with the two carbs on a small port head.
I am going to start by putting in the next size larger venturies.
At some point, I'd like to put on a 3rd carburetor and I'd like to find a 3 carb Nicson for this (all other speed / dress up items are also Nicson and I'd like them to match).
Or - should I stick with the two carb setup and switch to a big port head?
Questions question - anyone with experience with GMC sixes with these kinds of issues?
Compression is 9:1 with forged pistons, 1.84 intakes 1.6 exhausts with a Delta reground cam (profile 254S), dual cast exhaust manifolds with plenty of breathing through exhaust system. I am still running 6V so it has a pertronix with 0.6 Ohm 40kv coil running 0.045" spark gap.
