Unless you're part of a racing team or have $100,000 to spend i doubt you'll get your car to go 9's or even 10's. I think to get mid ten's in the 1/4 mile would require you with your weight car to have about 600 horsepower and be completely gutted with ladder bar suspension....basically with bolt on parts your could probably hit mid 13's for not a HUGE amount of money, but any more and i'd say you're looking for some serious funding.
Here's how 1/4 mile times basically work (i'm no expert, nor do i know much, but this is what i know -the times/mph i will give will likely be incorrect, but i'm just showing an example):
there's your reaction time which is how long it takes for you to move, which is not included in your 1/4 mile time, and then as soon as your car triggers some lights the clock begins. a 14.8 second car like mine goes 0 to 60 in 6.2 seconds and ends the 1/4 mile almost at 90 mph. a mid 13 second car goes 0 to 60 in like 5.0 seconds and ends the 1/4 mile at like 105mph and would absolutely WASTE a car like mine. as the 1/4 mile times get lower the miles per hour at the end go up quite a bit. So in reality, to get a V6 mustang in the mid 13's would take a bit of cash especially in a heavy convertible, but 13's are VERY respectable and it's pretty intense for a street car (more than enough power to overtake someone very quickly when passing).
If you ever get to go to a track, you'll see just how much a difference .5 seconds in the 1/4 mile makes, much less full seconds.
hope this helps
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'84 Mustang 5.0 LX
My car