Here is a breakdown of all the plenums on the market:
Upper and lower plenums
Kinetix version 4
Made of plastic resin and currently on version 4. Early versions had cracking issues, but I have not heard of any issues with the version for. I had the earlier versions and they were...um...crap. Don't know about the new one. It DOES clear the strut bar, but in my opinion, this is not necessarily a good thing. I think it still restricts the airflow to the front.
Crawford version 5 or Cast Plenum
The version 5 is a stock plenum that has been modified. The cast one is a completely new casting. Neither allow use of the stock strut bar, which is probably good. Both produce good power. I happen to own a version 5 and it is going in on Tuesday.
2005 stock Nissan lower Rev-up plenum
This is the new OEM Nissan lower plenum from the 2005 Track and 35th anniversary models. It is the lower plenum, not the upper plenum. It has been tested by [email protected]
on a 2003 model (http://www.350z-tech.com/forums/index.php?showtopic=6725
). It shows a gain in HP, but a serious loss in torque (serious in my opinion). It will allow the use of the stock strut bar and it will look completely stock (good for warranty compliance).
APS Tall Boy
Not on the market yet and I am not familiar with the power claims. However, it is a new cast piece and you cannot use the stock strut bar. Likely the new Crawford cast plenum, this is likely a good thing.
SSR Intake Manifold - pictured above
Currently on the market, but I am not familiar with the power produced, reliability, or other features. I does completely replace the upper and lower plenum. Probably good for F/I. You can use the stock strut bar.
Kinetix intake manifold
Not on the market yet, but soon. Prototype phase has just been completed. However, given past experiences, I would not trust a kinetix product that is right out of testing. This is based on personal experience and the experience of others (I had a kinetix plenum version 1, 2, 3 and two separate sets of cats - nothing ever fit right or functioned well). This new intake manifold replaces the upper and lower plenum. It should be great for F/I and might clear the stock strut bar.
Offered in different thicknesses and some may allow the use of the stock strut bar. Also, I believe some of the spacers are beveled to allow the front to raised more than the rear. This should even out the air flow. I don't know much else about them. I do know the manufacturer posted dynos that show it is similar in power production to the Crawford plenum. I have not seen independent confirmation (but it probably exists).
Hope this helps.