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I know this is a bit late in this discussion but since this discussion started with examples of duel chambered plenums I thought I should toss this in here. See what Newman-Sharp Racing did to a 1987 (Z31) 300ZX 2+2 750 hp Turbo, winner of the 1987 SCCA Runoffs in class national championship. The pictures below are from: http://www.garymolitor.com/300zx/plenum/1.jpg http://www.vintagemotorsport.com/ Previous Issue, SEPTEMBER/OCTOBER 2007, page 22.http://tinyurl.com/b9eg8z http://www.garymolitor.com/300zx/plenum/Newman-Sharp-1987-Z31-1.jpg http://www.garymolitor.com/300zx/plenum/Newman-Sharp-1987-Z31-2.jpgI have an 84T Z31; the stepchild of the Datsun/Nissan Z lineage. I too am working on a duel chambered plenum for my car. I have posts on this project at. http://forums.hybridz.org/showthread.php?t=144523 & http://z31performance.com/forum/viewtopic.php?f=1&t=14536 & http://z31.com/forum/viewtopic.php?t=8388&start=0 I want to thank both MONZTER and turbobluestreak for their PM assistance.

Update: The green area represents the stock plenum outline mounted on the runners. ERG location is the current problem. The FICD/AAC and air control valves would be mounted on the back. There is enough room between the back of the new plenum and the firewall for these two components. This overlay shows the problem that exists with the water filler and the distributor. The easy solution would be to have a raised hood for the required clearance. Something I was planing to do any way.

Interesting. I will subscribe to your "VG30DE(tt) custom intake manifold" post to follow along.

It will be great to watch the progress of this creative build.

I thought about thread jacking Monster's First the questions and if you have interest on what this is all about and who I am, you can read on, view pictures and click on the web links. Question 1 How does one go about sizing a plenum?. My design is now 3.3 liters. Question 2 What is the proper way to find the correct diameter for the twin pre-plenum tapered feeders that run the length of the plenum? The throttle body ID is 60 mm in diameter or 28.269 centimeter² and each of the 6 runners has an opening of 3.68 mm or 10.58 centimeter². Question 3 Does it matter whether the pop off (not blow off valve) valve is mounted close to the front of the plenum or the back? Most of the pop off valves I've seen have been mounted to the far end of the plenum away from the throttle body. I hope some of the members here that have had input in to MONSTER's Plenum can give me some direction. There is are a couple questions toward the end of the long post so please bare with me. Best to start with an introduction. I'm 68 years old. Have an MA in Professional Art. Worked as a college instructor, sales engineer and marketing professional and by avocation a mold maker. I have owned my 1984 Z31 (300ZX) since it was new. I have been working on it for the past 5 years and rebuilding it with an American street rod aesthesis. See the link at the bottom of the page. During the process I started making some Z31 parts for resale that are not or no longer available. There is a link at the bottom if you care to see that they are. I don't post here as I've really not had anything important to say. I'm mostly over at Z31Performance.com but do check the posts HybridZ from time to time. Over a year ago I started to follow MONZTER's new plenum design discussion. As it turned out, I was on my second attempt at build a 1:1 scale model of a plenum I had been thinking about it for a little over a year. I even went so far as to cut up an extra Z31 plenum laying around for parts to use on my model. I used the same ideas he used derived from the Audi and Norwegian hand made plenums. I did a quick sketch of my idea and sent it to him asking what he thought. His reply was positive and did and without me asking he did a CFD flow analysis that showed good results. I set the plenum project aside while I worked on other projects. Then along comes a offer I could not refuse from a new Z31Performance members to CNC my plenum or a nominal fee. I have Jeff Hartman's book, "How to Turn and Modify Engine Management Systems" and was hoping to find some useful information in chapter 12, "Designing, Modifying and Building Intake Manifolds." But nothing specific was provided and it appears Grape Ape Racing web site is down For the past two days I have been search the web for information on how to size the volume of a plenum. Here are some of the answers in found. "1 1/2 times a runner volume" Jeff Hartman's book states, "For three cylinder or six with twin plenums, each plenum should be 65 to 85percent of the displacement of the three cylinders being feed. For engines operating closer to 7000 to 7500 rpm, reduce plenum volume by 10 to 15 percent. For a power boost to 3500 the plenum should be 30 percent larger." "It depends on your RPM range, Engine size and intended use of the engine. For instance, an engine utilizing an automatic transmission will have a much smaller plenum than an engine using a five speed. An engine with a five speed behind it can use another 20% more plenum volume." "Regarding non-turbo engines, if the engine carb. is 'too small' you generally want a large plenum. If the carb. is 'too big' you want a small plenum. I have heard the number 150% of one intake runner and cylinder head intake port volume as a good starting point. Heavy cars like small plenum volumes, light cars like large plenum volumes." (My opinion ... WTF?) Your suggestion will be appreciated. Z31 project page http://www.garymolitor.com/300zx/300zxmainpage.htm Z31 parts for sale http://www.garymolitor.com/mfp.htm My art site http://www.garymolitor.com/ Polished Z31 Plenum Cut up Z31 Plenum Clay Model Foam Model My drawing, top view My drawing, cross section

He is a better and smaller version that you can print on 8.5-11" paper. http://www.garymolitor.com/head-porting.pdf