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Old 04-03-2002, 08:54 PM
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Question Help with calculating dome size on pistons.

Alright, I am inquiring about a set of Keith Black 119 .030 over pistons, I am wondering if anyone can either tell me what the dome size is in CCs, or if you could tell me how to calculate it? I am trying to figure on a compression ratio.


Edit: Also I am wondering what is the maximum compression ratio that can be safely ran on pump gas.

[ April 03, 2002: Message edited by: Vsanthos ]

[ April 04, 2002: Message edited by: Vsanthos ]</p>

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Old 04-03-2002, 09:36 PM
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An easy way to check dome volume is to take your piston and a big piece of plastercine or plumbers putty and make an impression, fill the impression with a thin oil like auto trans fluid etc. Measure as you add using a syringe.

You can also use a large beaker and invert your piston and dip just the dome and measure the change in volume. I use the plastercine method and cover my impression with a disc of clear plexiglass close to the size of the piston. In this plexi I have a 1/8" drilled hole through which I add the fluid, this way is a little more accurate and lets you see if all the air is out. A glass burette is the best way to add the fluid and I seal it to the plexi with the putty, makes a hell of a mess though. This way gets you within a cc or so.

Maximum compression? I would say depending on the head design, wedge heads could go to 9.5 to 10.0. 4 valve pentroof chambers could go to 10.5 to 11.0. Personally I don't run more than 9.0 to 1 on the street with wedge head designs just so I can get the initial timing and the advance the engine needs to perform well.

Others may disagree, but Canadian gas is notoriously poor in octane. The best premium around here is 92 octane.
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