[s-cars] speed vs. weight, 10 kilos and 0.4 seconds & Mahoney JNR ersatz M3 CSL

[MLP@DT]

Sorry don't post very often, but still skim the list traffic digest from
time to time. 

Took a look at Mr. Mahoney's link,
http://www.usautoparts.net/bmw/models/m3_ltw.htm
(and My .002 Bill~rules is for the birds~M  http://tinyurl.com/oymcot  Bill
that is an awfully tiny bird, I'll be Paul's is the size of a 747)

 and got to wondering what opinions or insights the list might have on what
10 kilos, or in Mahoney's case "200-300 lbs depending on how Bill were
optioned"  may be worth on a track  :-)  

Basically, what rough rules of thumb does one look to when guessing about
the performance effectiveness of shaving a little weight off a car?  I'm
just going to cut & paste the notes I took on Mattchet's F1 commentary on
the question:

Weight & Speed ~ 10 Kg / 22 lbs equals a theoretical @ 0.4ths of a second
time advantage on the Shanghai Circuit.

Steve Matchet Formula 1
Shanghai Circuit ~ length 5.451 km / 3.387 miles
Lap Record (2004 M. Schumacher):  1.32.238 seconds
2009 won by Sebastian Vettle RBR-Renault pole position 1

2009 Qualifying Positions:
Vettle Pole 1 w/ 		1.36.184 lap
Alonso Qualified 2nd w/	1.36.381 lap
Webber 3rd w/		1.36.381 lap

Race Vettle finishes 1st, Weber 2nd & Button 3rd (started 5th); Barrichello
4th (started 4th).
Fernando Alonso finished 9th, pole position 2.

Mattchet's comment on the qualifying times was something to the effect, now
that teams have to publish their fuel loads at the start of the race, a
"fuel corrected time" between the Red Bull chassis (Vettle & Webber's cars)
and Alonso's R29 Toyota, based on 10 Kilos (Alonso was running "very, very
light" by @ 22lbs), "ought to" make Alonso's car something like 0.3ths of a
second faster than Vettle, but he wasn't.  Alonso was @ 0.2 tenths slower in
qualifying. Taking Alonso's 10 kilo weight advantage, per Matchet's
comments, into account, Alonso's is really something like 0.4 to 0.5 tenths
off the Red Bull pace.  

Questions:  What math goes into Mattchet's calculations that Alonso "ought
to be 4 tenths faster if he's 10 kilos lighter?" What rough rule* or rules
of thumb** are used in estimating a .4 to .5 lap times based on a 10 kilo
weight difference? 

Formula 1 2009 minimum car weight, INCLUDING driver & fluids, #1,333 lbs;
Note, Minimum weight is set to increase for 2010 per 5/18 Autoweek blurb to
#1,367 lbs ". to remove an inherent performance disadvantage for heavier
drivers since the introduction of KERS ~ a KERS battery weighs @ 77 lbs."   

Fuel "ROT"
Water weighs @ 8.3# lbs per gallon, Fuel floats on water; 
Gasoline @ 6.1 to 6.25# per gallon, weight varies with temperature
Jet Fuel (basically kerosene) is heavier, weighs @ 6.7 - 6.8# per gallon
Diesel "most commonly used weight is 7.3# per US gallon."