Question about 802.11b and 802.11g

Hi,
I have run experiments with 802.11b and 802.11g and the results are extremely different. I would like to know if someone could help me identifying the main differences.
I am using a max 3 hops ad hoc wireless network. the maximum throughput I get with 802.11g is 8Mbps so the difference is the modulation scheme. 802.11g and 802.11b for these rates share the same scheme: DSSS with CCK, right?
Someone can help me?

Thanks,

R.