Thread: Making Combustion Chamber Bigger

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Faylur, first off, don't assume they are 59 cc's until you've poured them yourself. You can find a burrette and sealing plate at summit for about $100.

If you are going to enlarge the chambers, bolt the block to the engine stand. Clean the heads of oil and coat them with Prussian Blue (machinist's dye). Bolt the heads to the block with a couple of bolts and without gaskets. Turn the block upside down and use a sharp-point scribe to run around the top of the bore and show where the inner diameter of the cylinder will be on the heads. Remove the heads and you will get a good idea of how much unshrouding you can do. Personally, I'd prefer to cut the bowl around the valves with a cutter indexed in the valve guide bores than to sink the valve seats. Take one head to the machine shop and have the machinist cut just one chamber with a round-tipped cutter so you have a nice curve from the seat to the edge of the chamber right up to the line you scribed. Then pour that chamber. If it comes out on the money, have him do the other 7. If not, plan B.

If you can, use a valve that will leave 0.200" between the edge of the valve and the bore of the cylinder. Done this way, the head will probably flow more than if you put larger valves in and shrouded them all over again.