Boosted Falcon

Just wondering if someone has done the maths or if there is a formula for calculating comparable power to weight ratios.
What I mean is if you have a car weighing 1500kg producing 400RWHP, what RWHP would a car weighing 1800kg have to make to do the same times. Assume the cars have the same gearbox,diff ratios and tyre size, so the only variable that changes is the power/torque.
Now for this exercise I am talking 1/4 mile times as circuit racing has to many variables.
The three car i am thinking of is:
A. TD/TC Cortina
B. XD/XE
C.BA/BF

on the vicroads website there was a power to weight calculator on there for when p platers could have v8's... dunno if its still on there.
im sure if u google a power to weight calculator u could find one...

Just looked up the vicroads site and not bad but not what I was after. But in the google search results I found this site
http://www.letstorquebhp.com/calculator.asp which seems to be what I'm after.
I would still like some real world experiences in relation to what people have found as number crunching is good but actual results are more telling

in theory you can calculate it i guess.
but you also get the issue of torque to weight ratio.

and also i guess you have to assume the same grip levels despite a raise in power/torque

PA/WA=PB/WB

PA=power car A
WA= weight car A

etc. As you want the same ratio, they are equal. Make PB the subject thus

PB=(PA/WA)*WB= 480HP for car B to have the same P/W as car A (according to your eg)

Same for torque

TB=(TA/WA)*WB

Screw other variables as air resistance, tyer grip, weight distribution would make this all derp and based on power, torque and weight the cars should be within... I dunno 0.2sec or 10% of each other (figure made up, go through drag DB and test theory).