Ok, I was pondering this because of a suggestion made here a few years ago while working a V6. Varying the runner length changes the power-curve and, in some cases, can actually increase power.

Well, I'm looking at my S4, getting ready to put it back together, and I'm wondering what would be the effects of putting a 1/4" or 1/2" spacer in between the LIM and the UIM? There's room for 1/2" I know, but I odn't know beyond that. Thought it'd be something worth taking a shot at. So what do you guys think? When I was naive I let the guy convince me that it'd give me 5 more hp per 1/8"...lol...I was a real noob then...

 

It would tune the power curve for lower RPM than stock . . so theoretically you would gain some midrange at the expense of top end power. Practically speaking, 1/2" might shift the power band about 500rpm in my humble opinion, so if you have the spare time, I would give it a try if the UIM and TB will still fit under the hood after the spacer is added.

 

I think I'm going to set everything up to near stock levels then do it, or else I won't have a comparison...then again, maybe not...