102 and 302 Compression Ratio

[DeanFHobart]

Anyone In The Know,

What is the compression ratio of a typical race ready 102 0r 302 ?

[DeanFHobart]

Compression Ratio

Dan,

Thanks, but that is the Compression psi not the Compression Ratio.

The Compression Ratio will be something like 8:1 or 9:1 or ?

[nicf14]

Just take the volume when the ports close to tdc (swept volume). Add that to the volume of the combustion chamber at tdc and then divide by the volume of the combustion chamber.

[pat]

Compression (psi) is not the best measure of ring seal although it is easy to do but a good compression gauge is also important. You will get slightly different results depending on whether the engine is hot or cold. A much better indicator is "leak down" where a leak down tester gauge is used in conjunction with a compressed air system to measure compression loss versus a starting value. A 5 to 8% loss would signal it time to hone and re-ring. So many things impact compression...ring end gap, type of hone, cylinder bore roundness, deck height, cylinder head measurement and the piston to cylinder wall clearance. The 102/302 are relatively low compression engines and using a pull cord a reading of about 125 psi is typical with no more than a 5 psi variance between cylinders.

Pat Kants
Kants Racing 83-CE

[DeanFHobart]

Compression Ratio

Thanks for this information, but what I'm after is the Compression Ratio.

[CSR4C]

Check your Yamato manual

The specs. section in both the 102 & 302 manuals list the compressin raito as 8.6 to 1

[sam]

The 8.6:1 compression is the full stroke measurement.

Hang on while I do Nic's formula for effective compression ratio

[DeanFHobart]

Compression Ratio

The specs. section in both the 102 & 302 manuals list the compressin raito as 8.6 to 1

Thanks Darrell.

That's exactly what I wanted. I don't have a manual.

[sam]

The effective compression ratio is 5.975:1 ... 6:1

The number to use when looking at what gas to run would be something between the 8.6:1 and 6:1 ... approximately 7.3:1