Difference between revisions of "Increased compression ratio"

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Latest revision as of 16:44, 8 July 2018

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Increasing compression increases the efficiency of an engine with all else being equal. However, this requires a head gasket swap, head shaving, block shaving, or new pistons. It's an involved process, but if you have the engine apart already its worth looking into.

Instructions for mod

How increase compression
Increase engine displacement. By boring or sleeving the block, or stroking the engine (increasing distance of the piston stroke).
Decreasing combustion chamber volume. Changing cylinder heads to ones that have a smaller combustion chamber, Switching to pistons that are flat or slightly domed. This is the most effective way to increase compression ratio.

Information required: A listing for different ways to do this if its different on different types of cars

User experiences

Increasing compression by a full number normally results in up to a 1.4% increase in engine efficiency.

User data
User Name Car Make, Model, Year Cost of Mod Time to Perform Mod MPG Before Mod MPG After Mod MPG improvement guess Instruction Link
Example Data Saand Example Data Mazda, 626, 1991 Example Data $5 USD Example Data 1 Hour Example Data 27.2 Example Data 29.8 User mod detail or measurement detailed data

You can figure how much pressure your engine will develope on the compression stroke with a simple formulia. p = PxCR^r (pressure times compression ratio to the power of 1.4)

p = compression pressure

P = 1 atmosphere in most cases

CR = compression ratio number

r = specific heat ratio for working fluid, for air this is 7/5 or 1.4

Problems / Consequences of mod

Increasing compression can lead to knock with lower grade gas and may require a higher octane to prevent this.

Information required: What are the consequences of the mod, Eg: drivability issue, stalling, engine wear,


Forum thread links

Wiki thread

External links

popularhotrodding article on compression ratio