i dont have the strut bar over my engine, and i was looking at either the 5/16, or the 1/2.....

since i dont have the strut bar in the way.....i can get the 1/2 iso therm spacer, and keep my engine cover on without any mods right????

I think you need 5/16 to keep the engine cover.

I have the 3/8" on mine and I was barely BAAARELY able to get the engine cover on. It's actually touching the plenum and ever-so-slightly bowed as a result of touching the plenum with the spacer on there.

With the 1/2" spacer, you will definitely not be able to use the cover, unless your car is newer and maybe they redesigned the engine cover since then.


You don't get much of a difference anyways from the 5/16 to the 1/2", so if you really care about the engine cover... just get the 5/16".

The engine cover will not fit with the 1/2" spacer unless modified.

If you want to keep the stock engine cover look, checkout citimunky. He's got a MD 3/8" spacer with a Stillen Strut Bar. Looks clean.

1/2" will only give you 1-3 more peak HP, while the 5/16" gives you more usable power across the mid powerband. Unless you're doing a lot of high RPM driving, just go with the 5/16" and call it a day.

My setup is just like partyman's.....I have the 3/8" MD spacer and could barely get my engine cover to fit without slightly touching the liner inside the hood. I had to remove the rubber blocks on the underside of the engine cover AND flip the 4 grommets that the engine cover screws pass through in order to get it to not rub....

I also had to use some silver touch up paint on the engine cover to try and mask the rub mark.


....so since the 1/2" inch is thicker than the 3/8", you'll def rub with it (like the others have said) so go with the 5/16".

If I remember correctly, the difference between the 3/8" and the 1/2" was almost not detectable even on a dyno.... it might have been like .5 to maybe 1 peak HP. The original airflow tests done by some company who designed an aftermarket plenum or spacer for our cars proved diminishing returns per extra increment of spacer height beyond about 5/16" of extra spacer.

5/16 deff the way to go

cover will fit with 1/2"... invert the grommets and you'll be fine.

Get the 1/2" spacer, remove the cover and have your plenum polished, that's what I did. Looks great.