Headers make much of a difference?

[Dark_5.0]

I put 1 5/8 BBK equal length headers on my stang and it feels like I lost some low end torque but it feels like it pulls harder in the top end over all I think I probably lost ET but I got the 1 5/8 cause I plan on puting on some trick flow heads later this summer

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88 mustang gt convertible bored to 306 BBk equal length headers mac cold air fender kit cowl hood nitto drag radials ford racing clutch flow masters h-pipe 160* thermostat 16 degrees of timing electric fan off 94' t-bird jacobs electronics cap and wires