compression ratio calcs
1405cc engine (74.2x81.28)
the pistons are not dished, but have slots/shapes/chambers, in the shape of the mini combustion chamber. apparently to improve squish.
doing a dry build i managed to get what i believe to be a very accurate measurement with the perspex/burette system, identical to cylinder head volume measuring system. Piston tdc (with DTI) perspex on, sealed to cyclinder with vaseline, kerosene in through hole
=7cc
What are peoples opinions on the accuracy of this? IMO it is a comprehensive measurement of the volume up to the deck of the block, accounting for the volume between piston/deck, the piston dish, and the ring lands etc etc? becuase of the shape of my piston crown its impossible to measure these individually (in the shed anyway)
so for the sake of getting on with it, i was going to use the above 7cc, plus the gasket... plus the combustion chamber, and done. Comments?
Moving on to the Combustion chamber. Mine are 22cc, on a well worked and head, its been skimmed in the past. Recently used on a 1293 at 10:1. Because of my 1405 situation i need to gain some volume to get the CR down. I need to loose 6cc and i don't think i can get it out of the head without ending up with a ridiculous chamber shape, Or can i?? there are some crazy shapes on TurboMinis.... from missing beaks, to totally milled out chambers. Im wondering if i should start carving mine up or not. Vizard has solutions, sinking the valves deeper etc, but im on a budget - and i could start with a new casting for the same price as that. Castings expensive here.
Theres a copper decompression plate here, i suspect it was going to be the gasket back in the day. 74x1.4mm... volume of 6cc...
looking at 6000rpm max on this engine, 10.1-1 ratio.
