i know this topic has already been asked im sure but im goin to ask again lol
do any of you know what wioll work best a 1/2 engine spacer or the 5/16 spacer. i am looking for the one that gives the best results like gas mileage and HP if any one has results or numbers that will help me decide thanks and o ya it is a 03 350z touring auto tran 40,000 mi if it makes a diff on auto or manual thanks again

 

5/16" u dont have to replace the strut bar
1/2" u do

gas mileage..i dont the exact answer for that but i think 1/2 gives 1-2 hp more than the 5/16

 

https://my350z.com/forum/search.php

 

Adam @ Z1 is making over 300 whp NA with a 1/4" spacer... Of course he's also done lots of internal work to the motor. :-)

 

Spacers have been discussed at length in the intake forum.

 

I have one 5/16"...never installed....make an...offer?

 

It depends on the RPM range of interest.

The 5/16" makes a higher average across the entire range.
The 1/2" makes a higher peak near redline.

This is a comparison of average power at High RPM.





And this is a comparison of average power across the whole RPM range.


So there are differences.
Which one to get depends on your driving priorities.