Ralph, you're right. the spyder is allowed a larger engine because it is non-turbocharged. if it was a turbo it could only use a 2 liter engine.
I was looking at the regulations and got it all mixed up when I wrote it down.
Point was, LMP-2 is supposed to be slower than LMP-1.
In ALMS, rules are changed almost every week to try and even out the competition. Weight is added to the winners, the loosers get a break. Thewre has been around 13 of these "competitor bulletins" so far this year, in 2005 they made 25 of them.
I don't really like it at all unless one type of car has a huge advantage and the competitors can't compete as in the case of the R10. That's when it ruins the racing.
Just like can-am in 73 and 74, porsche was kicking butt and it discouraged the competition to the point where they decided to look elsewhere, the series basically died because of it.
edit: here's a link to hte competition changes:
http://www.imsaracing.net/imsaNS2.cfm?h=/2003/series/alms/header.htm&p=/2003/competitors/indexnewalms.htm