which capacitor would work best for a high voltage circuit? 1.05 uF @ 2100 V or 4.7 uF @ 450 V?

hello, im trying to make a hv ciruit to ignite annoying fuel to air mixtures and require a capcitor in my circuit... which capcitor would work best?
this one...
http://cgi.ebay.ca/4-7uF-450V-HIGH-VOLTAGE-CAPACITOR-RADIAL-LEAD-X4-/230325359544?cmd=ViewItem&pt=LH_DefaultDomain_2&hash=item35a07613b8
or this one....
http://cgi.ebay.ca/1-05-uf-2100V-Microwave-Oven-High-Voltage-Capacitor-/270611299459?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item3f01b0bc83

if so, then why?

thanks for your help i really appreciate it....

caarntedd7 years ago
Just to go off topic for a second, you have a fantastic user name. I am a firefighter and have been on fire three times in my life...........none of which had anything whatsoever to do with my job. Keep up the good work and remember, fire always makes it better.
Assuming you can make the voltage, then the 1 uF cap because
Energy stored = 1/2 C V2

So the cap 1.05 uF can store (1.05 x 21002)/2 Joules.

If you can't make 2kV, then you'll STILL win with 1 uF if you can make more than 900 V .

Otherwise, just get the 4.7uF. And be very careful.

Steve