The Lotus has a smaller engine so by default it'll put out a higher exhaust tone (frequency) than the 86. No amount of changing exhaust piping will fix that. It's physics. You might be able to rig up a series of resonators to cut out lower frequencies though but that just seems kinda silly to me.
http://www.fsae.com/forums/showthrea...c-Exhaust-note
http://www.physicsforums.com/showthread.php?t=475510