Originally Posted by 383_Gladiator
About to buy my AFR 195's but idk if i should go with the 1034's 65cc or the 1036 75cc. any insight? shooting for 10:1 static compression. block zero decked, pistons have not been purchased yet.
My preference for a normally aspirated engine is tight chambers, there are a lot more active in getting oxygen and fuel molecules mixed together that are large chambers. Then I use a D dish piston to dial in the compression based on the needs of a dynamic compression for the cam, gearing and vehicle weight. The higher efficiency of a tight chamber more than offsets valve shrouding and goes a long way toward adding mechanical octanes to the engine which delays the onset of detonation which lets you also push the limits on ignition advance and fuel mixtures.
For nitrous and supercharged engines I go with an open chamber head, here there is so much product being dumped into the cylinder that unshrouding the valves becomes the more important feature vis-a-vis forcing close associations between oxygen and fuel with a tight chamber as this is being done by the mass of stuff being dumped into the cylinder. The short coming of this approach is a street driven machine where either the nitrous or the blower is a part time thing, these engines force a less than optimum efficiency when just cruising around.
There are a lot of Dynamic Compression Ratio (DCR) calculators out there, make use of them as your cam will negatively affect the Static Compression Ratio so the (SCR) needs to be well adjusted for that event at the time of selecting part. Keep in mind that large ports slow the low RPM flows an event the engine will react to like running a bigger cam at slow speeds, so this combination if used on a street engine with mild gears will want tight chambers to invigorate the mixture and more compression to overcome the lack of low speed mixture density in the chamber. This effect will be present at all RPMs under the max torque peak and will be increasingly apparent the further under the torque peak the engine is operated.