I've built a few hot 235s, and here are my obervations from doing it:
The main problem with 235 port flow is the fact that the ports are siamesed. The adjacent cylinders share intake ports, and the #1 and #6 cylinders have their own exhaust ports. 2-5 use siamesed exhaust ports. Bigger valves aren't needed on a 235, cuz the bottom end will redline before it runs out of breath. 235 valves are only slightly smaller than some OHV V8 valves I've seen. Porting, polishing and bowl blending on the head ports shows some marginal improvements. Cutting the head about .040" and using the victor/reinz gasket will bump up the CR too. Have the block zero-decked and the rotating assy balanced. Cutting the main journals .030" and radius-ing the journal fillets will reduce bearing speed and help prolong main bearing life. But the crank is prone to flexing at high RPM due to only 4 main bearings. The later 230-292 engines had 7 mains for better crank support.
Clifford made a 260M mechanical cam thats pretty radical, pulls hard from 1,800 to 5,000 RPM with a rumpy idle. Use with dual-wound valvesprings and comp retainers and locks. Make sure to install new guides and umbrella seals. But you don't wanna twist a 235 past 4 grand anyway or you're risking a failure. Use recon connecting rods with new bolts.
Badger cast pistons and plasma-moly or iron rings are good for a street motor. The total-seal plasma rings seal off great, but WILL pull oil thru valve guides if everything isn't new.
The best performance induction setup is a single 390 CFM holley 4160 4bbl with 58 primary jets on a clifford single-plane intake. Dual-carbs work well too, but you'll be tuning some strange idle and part-throttle probs due to lower vacuum readings. Fenton headers with 2" duals and smittys sounds really good.
Ign is best done with a petronix conversion kit in a stock distributor. Use one light and one medium spring from a moroso advance curve kit. Put a piece of 14 gauge wire in the vac advance mechanim to limit total vac advance. Set base timing for 12 to 15 degrees BTDC.
Total cost is around 3 grand for a whopping 160 HP. Low-end torque for days... WHOOO!
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