Forums › Forums › Builds & Mods › Mazda 323 GTX – WRC for the Common Man – Part Deux › Reply To: Mazda 323 GTX – WRC for the Common Man – Part Deux
Been doing some seat of the pants math trying to calculate what the new compression ratio is going to be. Considering how much we’ve removed off of the head to bring it back to true, the concern is how much extra fuel (or higher octane fuel) I’ll have to dump in to keep it from detonating and pinging. Based this calculation off of a 15 thousandths cut on the head, along with some data and numbers pulled from Wiseco’s piston catalog. The change in combustion chamber volume (this is where the math gets speculative) was derived by considering the loss as a cylinder with a height of 15 thousands of an inch, and a radius one-half of the bore (I converted to imperial measurements for this step.) Using pi * r^2 * h, the volume of the imaginary cylinder was 0.11 cubic inches. Converting to metric, that’s a loss of 1.802557 cc’s (so much conversion, can’t we just use a real system of measurement?) Subtracting that from the original combustion chamber volume, which this online calc found to be 39.400 cc, left us 37.597 cc, or a 4.8% decrease.
Stock was around 7.8-7.9:1, depending on who you ask. Again, don’t trust these measurements because it’s entirely possible, bordering on a near-likelihood, that I did something wrong. Luckily, it doesn’t seem to have gone up a lot, so we should be in the clear!