comp ratios of various EA's

[jono]

Just reading some stuff about the place that claim EA81s were 8.5:1

 

started to look up some specs, guessing Aust delivery only

 

EA71 - 1600cc are 9.0:1

 

EA81   79 - 80 1800cc  8.7:1

............81 - 87 1800cc  9.2:1

 

EA82 carb listing only up to 87

 

1985, 1987  1800cc  9.0:1

1986...........................8.7:1

 

The aftermarket pistons been available over the years have been marked as for EA71, EA81, EA82

My bet is, they are a compromise one part does many NA engines. I get 180 to 190 psi cranking pressures from genuine original pistons in EA81, 82 with up to 500,000km , yet only 160psi on a donk with aftermarket coverall model pistons

 

EA82 turbo 1800cc 7.7:1

 

don't have NA mpfi specs but my 1989 mpfi NA has piston crowns that 'look

 just like the carb piston crowns - figuring mpfi and carb in our market got same comp ratios.

Reading of US ideas of mpfi and spfi being the higher comp rated original pistons, spfi being highest at 9.5 ?

 

Just curious now if US aftermarket pistons are so generic cover al models or a wider range available ?

 

The soup up tip from 16 years ago was to use EA71 pistons in EA81 for higher comp, but that would be genuine spec EA71 pistons.....I now work out 

Edited May 2, 2015 by jono

[coxy]

Off course those 500,000 KM Engines would have at least half a point of compression just from the carbon build up, So unfortunately compression readings are not the be all and end all especially when you take into account differing cam specifications and hence effective inlet valve closing points

[skishop69]

Yeah, all we got was the 8.7:1 EA81. You are correct though that if you order EA82 SPFI pistons and put them in, you get 9.5:1. You can also order special pistons from RAM Up to 10:1 IIRC.