I did a search and couldn't find a comparison between the motordyne and z1 motorsports plenums. They are both 5/16, I was just wondering if there were any major differences between the two.

 

They both do the same thing. Price is different. I went with the Motordyne Thermal spacer which is different in the fact it prevents heat soak. I believe Motordyne has a better following based on the cars I have seen.

 

powerlab 3/8

 

Comparative testing done several years ago by Sport Z magazine. The results may be posted here.

 

^ Results of this supported Motordyne 5/16 as the best, however i dont believe the Z1 spacer was included in this test.

 

Z1 is an angled spacer (thicker near the front of the car), which adds plenum volume where it is needed most.
AAM makes an angled spacer (probably same design), but showed less gains in the Sport Z magazine test than the Motordyne. Z1 was not included, so take these results as you wish.