Dyno testing from low rpm - any drawback???

[foler]

hello
I want to measure my car on dyno, but want to measure from low rpm, 1000rpm and above. Dyno is maha lps 3000 which can do this. Car is m3 e36 3.0 and want to see where vanos kick in power. Here is one picture what I want. Any drawback in measuring from low rpm?

http://img5.imageshack.us/img5/5086/scan0001msd.jp...