1) no the r does not fit the street lower
2) you would probably see a performance loss in the lower rpm range, but it would haul *** above 5k.
if i were you, id stick to the track heat
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1988 Mustang GT, T-5
3.08's, No Smog Pump (Shorty Belt), Dumps At The End Of Stock H-Pipe, K&N Air Filter (Stock Air Box), Removed Air Silencer
My Stang
My Site (Not Done Yet)