I've been searching around about the motordyne spacers and use of upper and lower plenums. I understand that the 05 benefits from using the 03/04 lower plenum and the use of the spacer. What benefits would the 03/04 G35 have by using the spacer and an 05 plenum?

I'm toying with the idea of getting on the bandwagon with getting a spacer, so I need reasons why I should get one.

 

If you were to put the 05 plenum and a spacer on an 03/04, your gains would primarily be at the top end of the rpm band. It wouldn't give you the broader range of torque and HP that just the spacer would in the 03/04.

For the best results in getting a meaty dose of torque (much more beneficial in racing) across the rpm band, with a very minor drop in HP near redline (around 2HP), you should go with the 5/16" iso thermal plenum spacer. This will also allow you to maintain using the stock strut brace.

We have them ready to ship!

 

if you put an '05 "revup" lower plenum on an 03, 04, or 05 AT engine, you'll lose too much power; you need the variable exhaust cam timing to make that plenum work. Only if you have a motor built to perform at significantly higher rpms than your stocker may the "revup" work for you.