With a straight tuned pipe (gotta wait on some easing up of the cash flow for the Irwin pipe) how long should my header pipe be? K&B .67 O/B going to be mostly sport running with bursts of full speed not racing. Stock carb, stock flywheel, 12" tuned pipe 2" expansion, Prather Lap Cat III, Prather 240 stock prop, 20% O'Donnell fuel