Actual compression with 3.4 max moritz?

[dd74]

I'd twin plug it and enjoy the high compression.

[jgparker]

I had to run 1.5mm of shim to maintain 9.5:1. I found that shims are available in 1mm and 0.5mm and can be stacked. The subject was faily well covered here:

Cylinder base shim, how thick is too thick

[emcon5]

That seems high for a piston with a fairly low dome. What were your dome and head CC measurements?

What is your deck height?

Tom

[snowman]

The following method measures the compression volume, exactly, without any math or measurements that are hard to make.

The engine must be out of the car and on an engine stand. The engine must be in good condition, ie good rings and valves. Remove the spark plug from the cylinder to be measured (its a good idea to measure all of them, as it will vary). Turn the engine so that piston is on TDC and both valves closed. Rotate the engine on the stand until the open spark plug hole is facing up and the spark plug mating surface is horizontal.

Now for the measurement. Obtain one of the following: A syringe, calibrated in CC, preferably a large one, ie 50 to 100cc. OR a beaker that is calibrated in cc, OR one of those long tubes that are calibrated in CC with a petcock on one end.
Next fill the cylinder (I will use the syringe for an example) up with one of the following: water with a small ammount of antifreeze mixed in OR water with a small ammount of alcohol mixed in, OR very light weight oil, like diesel fuel (if you are worried about rust or leakage into the crank case).

Now start filling the cylinder with fluid, until it is full, ie fluit level with the lower edge of the spark plug hole. How much fluid did it take? Thats the EXACT ammount of cc in the compressed volume. All varitaitons in pistons, valves whatever are taken into account. Very simple and Very accurate.

Next rotate the engine on the stand untill the fluid drains out, completely. If you used water, follow up with some compressed air to help dry the cylinder out and a follow with a couple of squirts of oil and rotations of the engine to spread it around.

Finally you can make the compression calculations (sorry you do have to use math at this point). You know the bore, the stroke, and the exact compressed volume, thats all you need.

If your a real purist, and anal about it, you could actually measure each bore to the nearest 10 thousands of an inch and the stroke of each throw, to the nearest thousandth, but knowing compression ratios to 5 decimal places is of questionable value.

[rdane]

TRE any follow up on the engine you were building? Dyno numbers and specifics would be great.

[ChrisBennet]

Jack,
Doesn't the spark plug take up some volume that wouldn't be measured using the fluid method?
-Chris