The design of the Librands 4.2.1 manifold makes the most of the low dynamic pressure from the preceding exhaust stroke evacuate the gasses from the current exhaust stroke as efficiently as possible. Having long primaries negates this 'advantage' at lower RPM...
I also preferred the smother 'turn' into the '1' collector pipe of the Librands manifold compared to the tight turn of the Aero Racing version. My previous experiences with manifolds on the 1.8L 'K' series engines in the Lotus Elise, drew me to the similar looking manifold from the same manufacture (Janspeed) that Lotus had used the 4.2.1 manifold on the higher power Elise/Exige S1 versions.
My 'seat of pants' detector felt a noticeable difference in power and mid range torque, once I had the Librands fitted. I would have thought that the 'Aero Racing' version would give a better advantage with power at the higher RPM's...
Anyway! I am a happy camper with the result!
Either way, either version is worth some Torque/BHP increases :>) MUCH better than the OEM 'bagpipe' that is a free flow 'disaster'!
