the roller rocks usdm motors are 9:8 as opposed to 9:5 for older usdm sr20's . Is that a big diffrence i know it's lower than the uk but all i know is the lower the number the lower the compression.....is it a ratio...how is that figured out?

roller rockers have nothing to do with compression. compression has to do with the volume of your combustion chamber, head gasket volume, and piston dish volume. you take the displacement of your motor plus volumes of comb chamber, head gasket(depends on thickness) and dished piston volume. that number you devide by only the volumes of comb chamber, gasket, and piston dish. you have to cc your combustion chamber and piston dish to get precise numbers...dont trust the numbers on paper. i got my forged racing pistons and it said the piston dish should hold 12cc but it actually held 13.6cc....doesnt seem like a lot but it made a .4 point difference in compression ratio.

i should have been more clear i meant the roller rocker motored sr20's 00-02

i should have been more clear i meant the roller rocker motored sr20's 00-02


00-01 rr motors are 9:8:1.

If i remeber well, the higer comp. is because of the combustion camber that is smaller than the older ones. The piston are different also, but i'm not sure if its the same size.

Mart

Hmmm then why did Nissan write it off as 9:5:1 on their catalogs and specs?

I remember there were different numbers given between the SE and G20 roller's but to me they are exactly the same, the differences were always in the torque section, maybe due to the different gear ratios?

9.8:1 because the dish is marginally smaller.

the ring land is also smaller, but unless you're making over 350-400whp, its not really going to matter.