valve spring change with heads on the car?

[fiveohpatrol]

i ended up just renting an air compressor from a rental shop, not too bad to be able to do it in my own garage

it's great, i can actually rev past 5400, it feels like its got more top end now

one thing kinda confused me though, when i was about half way done, i picked up a new and an old valve spring and squeezed them by hand, to my suprise the factory one was harder to compress? maybe just the new ones have a faster recoil or something, oh well i know they are a hell of a lot better that the 115,000 mile stockers

thanks guys

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88 Notch, B&M Ripper, 3.73's, Ported E7's, Explorer int. w/ ported lower, pulleys, 1.7RR's, BBK headers, off-road H-pipe, flowmasters, subframes, 65mm TB, March ram air ,MSD coil, U/L control arms, 155lph f/p, Crane Adj.FPR, Nitto drag radials, best 1/4--> 13.76@101.4 on a 2.17 60ft