[sohc_my_dohc]

jdawg is absolutely right. i've been using this method to tune my cars for IDE and have showed it to several others members. now officer_cartman i see what you mean when you stated that the % changes after you install each part but that doesnt play a factor because the PR changes accordingly. For example, if i installed a Greddy Turbo kit, if you will, and the pr showed as 245 (87.6%), if you were to use the simple cross multiplication formula provided by the OP you would get 279.68 PR. now if you then install another turbo kit, it may show up as 240 ( 80.4 %) giving you 298.5 PR. now you see givin that the 2nd turbo shows a lower PR before calculation, the % is lower accordingly to provide a higher number at 100%. I'm sure i've lost some of you but trust me this will help save you TIME AND CREDITS. If some of you are confused by the simple formula then I can provide a more simpler way of explaning it. FIRST, you take the PR right after the install. THEN, you multiply it by 100. After you have done so, you take that number and divide it by the % that is given. THEN you should have the PR at the parts value at 100%.