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Gutted intake

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  • Gutted intake

    i picked up an na intake plenum from a junk yard and i am planning on gutting it. i know the basics of what i have to do but not completely. iv looked a little bit for "write ups" but didnt find alot. does anyone know of some detailed pages of write ups?


  • #2
    basically you have to take everything from the inside with a milling machine. try not to go too deep, not past the bottom plate and dont take any from the sides and back. just look for pics of some "in progress" and you will see. if you are too poor or dont have access to machinery, but have a lot of time on your hands, i mean a lotttt, you can use a dremel
    Must Go Faster, Faster Untill The Thrill Of Speed Overcomes The Fear Of Death.


    • #3
      i don't know of any writeups , but i have recently done it with a die grinder.... ill give you some tips . if you can use a lathe DO IT! it was a pain for me and it took me just about a whole day , the hard part is getting the center "divider" section out , i started by cutting parts of the top off , so i could see inside the plenum , once that is done and youre left with the middle section you are going to have to find a way to get all of the center section cut off , i had a problem with this , because either my dremel disks werent big enough to go thru the whole thing or my air cut-off wheels were to big to fit inside the plenum . i ended up taking a mallet to it , it go it off but i also broke a section of the front piece that will have to be welded on . after that i advice you shape the entries to the ports , you dont have to get too perfectionist with this , just make sure theyre a bit round . i also went all out and ported the ports to about 40mm ( stock is about 36-37), theres no point in this if you dont also port the gasket and the lower intake manifold , i may have done a bit of overkill with the diameter but since the stock intake valves are about 42mm i thought it was a good size .. all in all it has been a long project , its taken me just about two months to get it where i am at right now ( only working on it on the weekends), im still shaping and grinding away on the lower plenum , and i havent gotten the plenum back from the welder .

      sorry for the rant ,i decided i thought it was going to be a quick little mod , but its take much longer than i originally thought , but i will have exactly what i want in the end . for 400$ or whatever yoy pay for an already made one its kinda worth it ....


      • #4
        I took some pics of unfinished plenum

        Terrible idea putting those wheels on...


        • #5
          Email me any time for tips/especially when you get the ports

          make sure to include pics to show where your at

          Do you have access to a high amperage tig welder?


          • #6

            And OoOOOoo... a cut out z in paper + spray bomb
            (Before anybody asks about the intake. I was just playing around with fibre glass and the whole tapered intake jazz.)

            But anyway, This is how I did mine. I used a mill at work to clean the insides out. Like the one guy said. Dont cut too deep. I unfortunately did around the ports. But, all I did was made those butterfly looking washers that cover the small holes. They also spaced the bolts properly for the lower manifold. I started using a die grinder to cut the top off. And it worked pretty slick at work when I had the air compressor that ran at a constant rate. But unless you have a pretty big compressor at home. It becomes a pain in the ass waiting for the thing to charge up.

            However, it is doable by all means with out a mill. It just takes some time for sure. Aluminum is cheese. There are tons of cutters that can eat it pretty easy for different tools.
            I sand blasted it as you can see. And also cut a nice flat surface for my gasket.

            Then I spent a little while with a jig saw cutting the top plate out of 1/4 aluminum and drilling/tapping the holes in the plate and plenum.
            Luckily the existing four bolt holes for the spiffy "nissan 3000" cover provided some solid mounts for starters. Then I carefully tapped six holes along the edges of the plenum. Which is a bitch! There are some areas where the casting has extra material for ...the air regulator? misc outer holes for wire harness supports? What ever the case, I could get some solid threads going. But the back two bolts that I made IMO are useless.
            The threads are pretty weak.

            If I did this again, I wouldn't cut the outer edges down so much while making the gasket surface so I have more to drill and tap.
            regardless, for an N/A it worked out great.
            The whole unit is sealed tight. No leaks that I know of. In the next little while we'll see if it can handle a bit of boost.
            If not, I will make another. I just saw a short clip of a super charged lexus with a ...plexi glass? cover for the intake manifold so you can see the 6 individual throttle bodies underneath. Of course that cover has about 30 bolts holding it down...

            I also wanted to add, I filled in that little v groove on the front of the manifold with JB weld. I figure it can handle about 500 degrees fahrenheit, I measured the temp of my intake manifold after driving hard and it was only about 130 I think after sitting for a minute while I grabbed my meter.
            I just sanded it down so it was...flush with the rest of my gasket surface.

            Sorry if this is kind of, incoherant. I'm pretty drunk right now.
            But anyway, there is my vague write up of the tig welder-less ghetto intake manifold I made.


            • #7
              Have you ran the plenum yet? no leaks?

              get a nice set of rotary files and try to follow the stock taper around the port as best you can. It is one of the most critical points in the whole plenum.

              Also for the holes on the bottom, take it to a shop and have them filled with a spoolgun, or tig.

              Next, put it back on the mill and remove the slag from filling the wholes, then you can go a step furthur and countersink the bolt holes like this:

              I think the top might very well seal, but I would want a few more bolt holes to fasten with along the sides as well, alluminum starts to warp as it goes from hot-cold-hot-cold, and eventually I think you might start to leak here and there.

              keep me updated email me if you have any other q's.
              Attached Files



              • #8
                BTW sorry, about saying you need more fasteners, I just saw them along the sides. Nice work so far by the way



                • #9
                  Oh yeah, I've been using it for about three months now. In all honesty, because of the gasket maker gunk I used for the lid. I really think I'm in for a job when I want to take this thing off to do the injectors. I dont think it's going to pull off just as easy as I was initially hoping haha.

                  Your's looks good. Keeping the bolts low pro like that pretty well maximizes flow as best as it can be.

                  The next one I make I will put a little more effort into. Besides the milling, I made the lid and had it on the car through out a saturday afternoon. So I kind of rushed things. Good luck with yours.


                  • #10
                    Both gutted plenums in pics look really nice. I was thinking about doing this but I have a few questions. The first is: 1. Are the four upper to lower mounting bolts long enough that if they managed to come loose that they would hit the plenum cover or would either they or the washer be able to fall into one of the ports? 2. If the four mounting bolts instead extended thru the plenum cover and possibly use small pipes or tubing on the outside of the bolts so the cover wouldn't collapse, would this add too much flow restriction? 3: On a 20psi boosted application, how many bolts do you think it would it take in addition to the four mounting bolts to keep the cover from leaking? How about if I JB welded the cover on besides? Thankyou for the pics, and you guys have been very helpful.
                    86 Turbo


                    • #11

                      You brought up a couple good questions. :?

                      Yes, having bolts/tubes running down through the plenum will slightly inhibit air flow. How much is anyone's guess.

                      JB Weld would probably work. If you do this be sure to buy a couple sets and be very careful with your overspill and seal. Leaks could really be a problem. Most guys weld the top but...I don't see a reason JB Weld wouldn't work. I would recommend having it welded but I kind of like the idea of the JB Weld.

                      If you go with the welded or JB Weld top you will have to have access holes to access the mounting bolts on the lower floor of the plenum.

                      Washers falling into the cylinders- anything is possible. I would suggest that you use appropriate sized allen head bolts with no washers. Alternatively you could add lock washers to the bolts and crimp them down so they will not come over the threads of the bolt.

                      End of the day...sounds like a lot of work and what ifs. I would recommend the L&P plenum. Besides what was discussed above, it has been proven to provide better HP than other plenum designs, stock or gutted.

                      Just stand back and throw money.
                      Performance costs money.
                      Reliable performance costs more.


                      • #12
                        I am in the process of doing the same to my old intake plenum. So far heres what i have learned:
                        -ONE of the most effective ways to initially gut the plenum is to use a plasma torch to hack away at it. If you dont have access to one of these, using a die grinder works, but its slow. Mills are also nice
                        -Its a good idea to cut the plenum's elbow off. Port out the short sides as much as possible, but be careful because the material is very thin. Also, port the "step up" as much as you can.
                        -I would argue that a properly ported plenum and elbow will benefit from the use of a larger Throttle Body. This subject has been discussed to great extent in other posts, and there is alot of information out there. Make up your own mind on this one.
                        -As far as cutting the trumpet shape into the port, a mill, die grinder, or dremel will work. If you use a grinder, be sure to get a proper aluminum cutting bit for it.
                        -If you hand grind your ports, rahter than using a mill, TRY TO MAKE EVERY PORT THE SAME! Here is by far the best way i have heard of doing this: Grind out one port to your liking. Make it perfect, just how you want. Set your gutted plenum on a flat surface, with aluminum foil underneath the plenum. Coat the inside of this one port with WD-40. Mix up bondo and pour it into that port. Stick a bolt in the middle of the bondo. When the bondo cures, you will have a popsicle-like mold which you can use to ensure perfect port matching. For example, when you grind out another port, stick the bondo-popsicle in it and see how it fits. Continue grinding until it fits perfectly.

                        My question is: What is the optimum diameter for the trumpet shape at each ports mouth? Keep in mind this is for my low boosted (7-12psi) turbo Z, with the supporting modifications.

                        "produce second."