engine pistons

[gunmetal72]

Is it possible to tell the difference between a high and low compression piston by looking at them?

 

[70aarcuda]

On a 340, generally the low compression pistons have 4 valve reliefs...and high compression have 2 valve reliefs.

you can measure from the top of the wrist pin to the to of the piston and add .492 to get the compression height of the piston...

340 high compression is 1.84,,,,low compression is around 1.72
360 should be around 1.67 for high compression

 

[Coronet 500]

The only way is to measure Compression Height, top of piston to center of pin and compare it to OEM with some mathematics involved.

If you have two, slide the pin into both and see which one is "taller".

 

[nm9stheham]

If those are 273 pistons, they are the lower compression ones... due to the 4 valve reliefs.

So what engine ARE these from?

 

[70aarcuda]

you can measure from the top to the center of the pin and add 1/2 pin diameter...492

 

[gunmetal72]

the are 340 pistons

 

[pishta]

Its my understanding that most if not all hi-comp LA pistons will have 2 valve reliefs only. the 4 reliefs are not side specific, while the high compression generally put more dome under the side opposite the valve, hence the 2 reliefs only. OEM 360 are generally dished so if you come across a Mopar SB flat top measuring 4.00 it could be a higher compression piston.