Quote:
Originally Posted by jlsanborn
Yep, target has been 11.0:1 static, which I think will be fine with the cam, a tight squish, manual trans and the right gear. We'll see! I ordered a better burette so I can more accurately cc the chambers. I'll also check the advertised -6.3cc piston tops. The trick is going to be figuring out how much to machine off to get to my target. My thought is making an imprint with clay, use the burette to fill the mold with the volume I want gone, then trying to measure the depth of that liquid. Any other ideas? We'll measure all four corners with one piston/rod assembly for an accurate zero deck and then use a standard composition gasket (0.041") for squish.
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The way I've done it in the past is to:
1. Put together a rod/piston/ring assembly and install it in its bore with a thin coat of grease on the top ring with an extra dab at the ring end gap.
2. Rotate the crank and bring up the piston top to exact TDC with a dial indicator.
3. Bolt on and torque the head with a gasket like what you plan to use. (I usually just torque the five bolts around the cylinder I'm checking.)
4. Rotate the block/head assembly on the engine stand to where the spark plug hole is looking straight up.
5. Use your burette to quickly fill the void space up to the bottom most spark plug thread.
6. Use the volume to calculate the exact static CR. (SV+CV)/CV=CR
7. Substitute the CR you want into the formula and solve for CV.
8. The difference is the volume you want to remove from the dome.
9. Your idea of using the clay and making an impression of the dome should work just fine. I'd probably use a pancake of clay with Saran Wrap over it and press the dome down until it was flat and level against the table. Then use the burette to fill the impression with the volume you calculated above. Measure the depth with a depth gauge or vernier caliper and you have your number.
10. Another way is to carefully trace the outline of the dome onto a piece of graph paper. Count the number of squares to determine the area, then divide the area into the desired volume to get the height. This may be slightly less accurate depending on your tracing and counting technique. I scan the trace and import it into my CAD program and use the irregular, continuous, splined shape tool to calculate the area. But if you don't have something like that, graph paper gets you pretty close.