I have heard that some years & models of 7's blocks have different compressions, is this true? And what about TII are they lower or higher? Is there a benefit for TII to have either lower or higher compression? Is there a benefit for n/as to have either? And what about high/low compression rotors, what are they about? And what are benefits of each for each model/year. And im a tad fuzzy on the whole compression meaning too, could someone explain plz.

 

Yes, the compressions are different in different year/model Rx7s. Quick breakdown...and somebody correct me if I'm wrong:



1986 to 1988 NA - 9:4:1

1989 to 1991 NA - 9:7:1

1987 to 1988 T2 - 8:5:1

1989 to 1991 T2 - 9:1



these are off the top of my head...I could be wrong. Normally..the higher the compression, the higher the redline and the better topend they have. NAs have higher compression because they can handle it, and it makes things smoother..turbo Rx7s had lower compression rotors put in them to keep them from detonating, lol. This is the main reason why you don't see turbo kits for NA rx7s...the higher boost pressure with the higher compressions will lead to short motor life. The higher compressions between the 88 and 89 NAs is what led to the extra 15HP or so....this is quick breakdown..anybody else wanna jump in on this? lol...

 

Those #s look right. I think you summed it up with your explanation

 

The 89-91 series NA motors also benefitted from lighter rotors and an improved intake to get the higher hp.