Are there significant differences in HP gains between the two? I read that a new plenum can increase up to 20hp, but didn't read much about the spacers.

Any advice to if I should go with one rather than the other, and why? Thanks!

 

id go with the plenum spacer
unless you got some money you wanna waste

 

No no... no need to waste money.

So it's about the same difference between the two? (except cost of course)

 

'03-'05 Non revup DE motor = 5/16th spacer
'05-'06 Revup DE motor = Mrev2 + 5/16th spacer

It would be best if you grab a drink and read-up on the topic.

 

Yeah I just recently stumbled upon the plenum topic. Working on understanding some others too. I'll go for the 5/16 spacer

 

Do a search there is a thread that had a comparison of the different Plenums and Spacers with dyno sheet.

 

This might help