How To Find An Engine's Compression Ratio
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- เผยแพร่เมื่อ 15 พ.ย. 2018
- When building any engine, one of the most important factors to consider is compression ratio. The parts you choose for your build are designed to achieve a specific compression ratio but that is totally dependant on what you're doing.
Compression ratio is the maximum volume of the cylinder divided by the minimum volume of the cylinder. Another way to put it is the volume of the cylinder at BDC divided by the volume of the cylinder at TDC.
What makes compression ratio so important? It directly affects the power level and operating range of a given engine application. Generally speaking, the higher the compression ratio of the engine the higher the potential power output. Higher octane fuels are required for most high compression engines to achieve optimum power output.
Strictly speaking, static compression ratio measures volume only, not pressure. There are high compression low cylinder pressure engines that are designed primarily for fuel efficiency and not just outright power. There are five variables that affect compression ratio and changing any one of these factors will raise or lower it.
First is the swept volume of the cylinder. If you change the bore or stroke of a cylinder, you'll change the volume of that cylinder and therefore its compression ratio.
Second is combustion chamber size. Increasing it will lower the pressure ratio and decreasing it will raise the compression ratio assuming that no other changes have been made.
Third is head gasket volume which means the gasket's bore size and its thickness. You might not realize it but the variations in head gasket volume can increase or decrease compression ratio by over half of a point.
Fourth is the volume of a cylinder at TDC with no other components. In most engines, the piston stops just shy of being level with the deck of the engine block. This small volume of additional space lowers the static compression of the engine slightly.
And finally, fifth is piston volume. A dome-shaped piston takes away volume which increases static compression. A dish-shaped piston adds volume, therefore, decreasing compression.
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How could i get sir
Tha right compression ratio for my engine ?
Is there any standard volume for every engine or you need to calculate to get the right volume?
Thankyou
The compression ratio and cam specs determine cylinder pressure. Too high of a cylinder pressure will give you detonation with pump fuel which is harmful to your engine. Normally 150-170 psi cylinder pressure will be fine. The closer you get to 200 psi cylinder pressure the higher the octane has to be to avoid detonation. Mild detonation can be avoided by retarding the timing. After that you have to lower the compression ratio or change out the cam for more duration to bleed off cylinder pressure. Hope this helps.
Don't you have domed and dished confused? I thought domed piston would increase compression ratio.
yeah thats what he said
@@s3904393s Him did, him said dat. ah da !
Where is the next video ?
No shit right!
Which compression ratio is good for a 6 inline engine? Hope you can help.
entirely depends on its application
Stick a bunch of saw dust in the spark plug hole. Turn engine over what doesn’t come out that is the compression ratio