Here's a quote from you mentor "Tuner" about timing and chamber and swirl port design.
"This spark advance requirement is very similar to the mid-late 80’s and early 90’s SBC heads (prior to the Vortec) with the spiral ramp in the intake valve pocket. There is a 318-360 LA Mopar head with the same port scheme. Both the Chevy and the Mopar head are allergic to more than about 25° total. Just like ‘modern’ fast-burn engines, no matter how high octane the fuel, advancing the timing more than a few degrees on a stock 235 only makes it overheat, even if it doesn’t spark knock.
Like any other engine, fast burn or not, the 235’s and the swirl port Chevy and Mopar, when the valve timing is adjusted to a more sporty profile, they like more initial timing, but they don’t like any more total."
And here on the Chevy swirl port TBI heads
"That intake port and head is one of the slickest things for torque and mileage since sliced bread. It will make good power with moderate cams like those used for street or short-track racing. The reason they get such a bad rap is they are absolutely, positively, no doubt at all, allergic to more than about 25 degrees of total timing, no matter what octane of fuel is used. Pump gas, 24 degrees, C16, 25 degrees, it won't matter. At "normal" 36 degrees they will knock and overheat."
