Build your own intake manifold

Posted by GreenGSX, Oct 29, 2007
Bolt-on Tech - 4G63 intake, exhaust, intake manifold, ignition, fuel system, cooling, etc.

  1. GreenGSX

    GreenGSX DSM Wiseman

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    Build your own intake manifold

    Why-

    Last year at Watkins Glen my car was fast but it really just fell on its face in 4th and 5th. The car was using a Cyclone Intake manifold with a waste gate actuator fabbed up to operate the secondaries. As much as I love it I think its holding me back. I normally take the car up to 8500 rpms and at those rpms the intake plenum is just too small. With a limited budget and the price of intakes going up I decided to build my own.

    Background theory-

    For the design I am following some basic manifold building rules. First the runners should be 9" from the plenum to the intake guide seat. The distance on a 4g63 head from the gasket surface to the valve seat is just over 4". We all know that the longer the runner the better a manifold performs at lower rpms. But there is another rule to follow. That is the plenum should be at least 2.5 times the volume of 4 runners (gasket to base of plenum). The tricky part is that you can move the whole power curve and peak horsepower numbers either up or down depending on plenum volume. Bigger the plenum the higher the peak horsepower.

    I want to make good power all the way up to 8500 rpms but I want some grunt down low too. My best design so far uses a 6" runner with a plenum volume just under 3 liters. I am planning on building the manifold by machining a 1/2" plate to act as the plenum floor that would feature velocity stacks (radiused entries) built in. That means they would be milled into the stock rather than rolling the end of a tube. I found ready made velocity stacks but they are $40 each and that's just too much money for me. I am planning on a plenum length of 16-17" inches with it tapering from 4" to 2.5".

    I got most of my design ideas from Google including this site.

    http://206.124.12.138/intake/

    The plan is a single plenum just under 3L in volume with 6" runners. That would give me about 10.1" from the beginning of the runner to the edge of the valve seat. From what I've seen I thought the 6" runners would be longer than what others have done and the .125 thick runners yield a 2" ID which is also smaller than what others have done. I think the slightly longer and smaller runners would help low end power when combined with a slightly lower than 2.5 times plenum volume. I think making more power up top is easy and I really don't think I can mess that up. Making power down low is another thing all together.

    What I think is that intake charge velocity controls cylinder filling at lower rpms and that like the 2G and EVO head design, smaller is better. At what point (rpm) does this smaller runner become a bottle neck I don't know. I am betting the farm that combining 1G port size dimensions with a big plenum would give me the best of both worlds. Much in the same way it would if I were to merely cut the plenum off a stock manifold and just weld on a bigger plenum. From my research that has been done with success.


    Tools-

    Table saw with carbide metal cutting blade
    Wood router with ½” round-over bit and dado bits
    Drill press with bits
    Metric taps


    Materials-

    http://www.onlinemetals.com/merchant.cfm?step=2&id=71

    This is where I sourced the materials for the build. I had some ½’ aluminum fixture plate that I got from the scrape bin at work but that can be purchased online as well.

    For the plenum I am using 4x4" OD 6063 T52 aluminum square tube with a .125" wall thickness. The runners are going to be made out of 2.25" OD 6061 T6 aluminum tube also with a .125" wall thickness. That would give me a 2" ID on the runners and 3.5" on the plenum. I chose the thicker .125" wall thickness to ensure maximum strength while giving the welder lots of meat to weld with. The cost between thinner stock was minimal.

    stockpicture1.jpg

    stockpicture2.jpg


    Building the manifold-

    Lube the blade with metal cutting fluid (Home Depot) and have at it.

    cuttingtheplate3.jpg

    This next photo shows how nice the of an edge the blade left.

    cutedge4.jpg

    Then I milled a lip on both sides of the 4" strip I just cut out. This will receive the box top after its cut.

    milledlip5.jpg

    Then I cut the bottom of the plenum box off so it would fit on the milled base plate.

    cutbottombox6.jpg

    trialfit7.jpg

    Later I'll cut an angle so the plenum will have a taper to it. For now it’s just dry fitted to see how it fits.

    plenbaseplate8.jpg

    Then I cut the 2 1/2" hole for the TB in another piece of 1/2" plate I had. I just randomly cut the hole so I could practice milling the velocity stacks.

    cutTB9.jpg
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  2. GreenGSX

    GreenGSX DSM Wiseman

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    The plan is to have a velocity stack on the back side of the TB flange as well. I cut the hole in a separate sheet so I would have a wide base for the router which is what I'm going to use to round over the edge forming the stack.

    Here are the pictures of the TB radius exit. This was my trial run with the wood router on aluminum and I have since improved my technique.

    TB%20radius1.jpg

    Next up was cutting the velocity stacks for the runners. I am using a ball bearing guided bit for the router which needed more than 1/2" of depth to cut the full radius so I cut another hole out of the plate material and then clamped the two pieces together. That way I had a full 1" for the bearing to ride on.

    cutting%20the%20velocity%20stacks2.jpg

    velocity%20stacks%20upclose3.jpg

    finished%20plenum%20floor4.jpg

    The next operation was to mill the backside of the plenum floor to open up the 2" holes to 2 1/4" so the runners would slightly fit into the plate. This is going to help properly align them and allow for a very strong weld. It should also make smoothing the entry a snap during the welding and assembly. I did that with my hole saw and my drill press.

    backside%20cutout%20for%20runner5.jpg

    runner%20in%20cut%20out6.jpg

    These next photos show the transition between the velocity stack in the plenum floor and the intake runner.

    runner%20and%20velocity%20stack%20mock%20up7.jpg

    runner%20and%20velocity%20stack%20mock%20up28.jpg

    Finally the money shot showing the plenum floor with the box and one runner mocked up.

    plenum%20floor%20with%20plenum%20box9.jpg
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  3. GreenGSX

    GreenGSX DSM Wiseman

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    Laying out the flange

    laying%20out%20the%20flange1.jpg

    scribed%20flange2.jpg

    Here's the flange. The bottom is notched to provide some overlap with the base plate and it has a 5 degree slope on the top to match the taper in the plenum. The idea is to build the intake in a way that allows the welder to crank up the power and really get a good weld. I think that when combined with the extruded plenum box will make it super strong.

    TB%20radius-13.jpg

    cutting%20the%20TB%20flange4.jpg

    machined%20flange5.jpg

    Here's a close up of the TB flange. It looks like the overlap is only 1/8" inch but both the base plate and the TB flange are from 1/2" plate stock which should allow for a strong weld.

    left%20side6.jpg

    Here's a money shot showing the partially assembled plenum box/floor/and TB plate.

    partial%20assembly7.jpg

    Building the end plate from 1/2" stock.

    back%20plate8.jpg

    I also had a bit of an accident while milling that plate on the table saw. It was getting to small to guide with the cross-cut guide so I free-handed most of the cuts. After I the last pass I held the piece just beyond the blade and I reached down and turned the saw off. As it spun down I took my hand off the piece and the vibration of the saw sucked it back into the blade. Man that makes a sick sound and the back plate went flying past my head. Good thing I've been wearing my full face shield.

    Once I found the plate the only damage was this gash. Could have been worse.

    oopps9.jpg
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  4. GreenGSX

    GreenGSX DSM Wiseman

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    Here are a few shots of the plenum with both the TB and end plate.

    side%20profile1.jpg

    back%20plate%20in%20place2.jpg

    free%20hand%20milling3.jpg

    Working the flange by hand with the dado cutting bit in the router

    ruff%20cut4.jpg

    Here it is after I've cleaned it up a bit.

    getting%20closer5.jpg

    getting%20closer26.jpg

    Here's a close-up after a bit of drum sanding

    drum%20sanded7.jpg

    Crushing the round tubes to match the oval port shapes

    crushed%20to%20shape8.jpg

    Here they are mocked up in the flange.

    runners%20in%20top%20plate9.jpg
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  5. GreenGSX

    GreenGSX DSM Wiseman

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    The intake and TB flanges.

    finished%20intake%20flange1.jpg

    finished%20TB%20flange2.jpg

    Here are the runners mocked up with the intake base plate and intake flange.

    runners%20in%20top%20plate23.jpg

    runner%20to%20flange%20gap4.jpg

    As you can see in the close up photo's of the runner to intake flange shots there is a small gap between the port shape and my crushed tube. That can be easily filled with weld and then ported smooth on the inside after everything is done.

    Counting the thickness of the top plate and flange the runners will be 6". Here is a couple of mock up shots.

    mocked%20up5.jpg

    mocked%20up26.jpg

    Believe it or not but making the throttle cable bracket was a royal pain. Getting that angle right and then spacing the cable bracket just so the cable lines up and has enough adjustment and accounting for the taper in the plenum. Much sailor talk was needed....

    throttle%20cable%20bracket7.jpg

    Here is a 3/8" plate that will be welded to the bottom of the intake to give me lots of meat to tap my manifold boost/vacuum sources.

    vacuum%20port%20plate8.jpg

    For good measure I've stepped up to a 63mm NT TB with no FIAV or ISC. I figure the car stalls enough already that why not ditch em when I can. Any reduction in water lines is going to be a plus in my book. There's also a polyethylene intake gasket too. That's supposed to provide a heat barrier to keep the intake cooler.

    NT%20TB%20and%20plastic%20gasket9.jpg
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  6. GreenGSX

    GreenGSX DSM Wiseman

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    Welding it all together. Please note that I am not a welder and that I hired a guy to weld everything up for me.

    This is the jig we built to hold everything together flat and true.

    the%20jig1.jpg

    onto the welding

    welding%2022.jpg

    welding%2033.jpg

    welding4.jpg

    finished%20runner%20weld5.jpg

    finished%20runner%2026.jpg

    finsihed%20runner%2037.jpg

    welding%20the%20runners8.jpg

    welding%20the%20end%20cap9.jpg

    welding%20the%20box10.jpg
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  7. GreenGSX

    GreenGSX DSM Wiseman

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    welding%20the%20box%2021.jpg

    All done!

    done%20side2.jpg

    done%20TB3.jpg

    Done%2024.jpg

    and finally, where any good race part belongs...the coffee table shot

    coffee%20table5.jpg

    Mounted on the car

    Mounted6.jpg

    mounted%2027.jpg

    mounted%2038.jpg

    Here's the new IC piping.

    new%20upper%20IC%20pipes9.jpg

    upper%20IC%20pipe210.jpg

    The last step in the process is to have the flange milled. Even though I built a jig to hold the flange flat while it was welded some warping was unavoidable. For $30 my local machine shop milled it flat for me much in the same way you would mill an aluminum head.

    Results-

    Like any custom race part some fabrication work after the build is needed to install it. The upper IC pipe needed to be redone as well as the vacuum hoses. I drilled and tapped the end of the manifold to mount the transistor to and since I use COP there was no need to mount the coil. I was worried that the 6” runners and box design would interfere with the brake master but it cleared with no issues.

    Performance wise I am very happy with the results. The car pulls strong from top to bottom and it will make power all the way to 8500rpms for me. I do not have the $$ to put this on a dyno so I have no real numbers to back my claims. I can tell you that last year I could hardly keep up with the GT3’s on the back strait at Watkins Glen and with this manifold I can match both the GT3 and GT2 all the way to the buss stop.

    The best dyno I could come up with is a friend with DSM link. The test car was a 2G with a 2.4L stroked motor running a BT28 turbo. Needless to say this car is a purpose built autocross monster. He agreed to do his best scientifically wise but everyone should know these are not very scientific results. To start with he did some baseline tests with the stock 2G manifold. Then he installed my manifold and went out and collected more data. It should be noted that this is a 1G manifold on a car with a 2G head so a adaptor plate had to be made so the bigger 1G ports would seal on the smaller ports of the 2G head. It should also be noted that there was no way around the ¾” lip at the base of the junction between the head and the manifold. Everyone can agree that for flow reasons this is not the best idea.

    The results were very good. Drivability was not hurt and the car made more power throughout the entire rpm range. The car made 28hp and 35 lbs/ft more power switching to my manifold.

    Lessoned learned-

    This was cheap. The parts to build were less than $50 and the welding and milling were under $100 so the total cost was less than $150. The whole project took almost three months of fooling around before it was finished. If I had to I could knock the parts out in a day and have it milled and welded the next day. Also, the biggest time killer was the flange. A band saw would speed things up some but in honestly if I could have bought a CNC'd flange for $50 I would do it.

    Its been on my car for the whole summer and personally I don't miss the cyclone one bit. I've had it off the car a few times to inspect it and so far so good with no cracks. Now go build you own.
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  8. kmoore

    kmoore Proven Member

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    Great Write-up
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  9. GreenGSX

    GreenGSX DSM Wiseman

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    spreadsheet.JPG
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  10. turbosax2

    turbosax2 Moderator

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    I can't open the attachments for some reason :(
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  11. kmoore

    kmoore Proven Member

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    I can't either.
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  12. GreenGSX

    GreenGSX DSM Wiseman

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    timsmanifold.GIF

    2gstock.GIF
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  13. GreenGSX

    GreenGSX DSM Wiseman

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    Download the two gif files and then toggle between the two with something likeWindows Picture and fax viewer to see the difference between the two manifolds. What's cool to me is that there is an overall gain in power all the way through the rpm range.
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  14. blcknspo0ln

    blcknspo0ln DSM Wiseman

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    Agreed, awesome job :) A huge difference is the much broader torque range.
    #14
  15. oldman420

    oldman420 Proven Member

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    I was just about to say, nice increase in torque at high rpm :thumb:
    Is that tuned after install?
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  16. 97 4G63

    97 4G63 Proven Member

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    Great work :thumb:
    but it seems like you need some good skills/tools to get the job done..
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  17. GreenGSX

    GreenGSX DSM Wiseman

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    There wasn't a lot of tuning done after the install. Remember from the first post that this is a 2G 2.4L autocross car with a BT28 turbo. I can tell you both runs were at ~20psi running knock free. Also keep in mind that this was a 1G manifold on a 2G head so there was a 3/4" lip between head and the intake flange. Although I like the results from the plots what I like even more was the response I got from the tester. He loved it so much he ordered one from JMF using my specs.
    #17
  18. GreenGSX

    GreenGSX DSM Wiseman

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    If you've used a router, table saw, and a drill press before this project won't be much of a challenge. I didn't draw up plans for each part I just started with overall volume I wanted for the plenum and then built the plenum base plate based on the length I calculated with the spreadsheet. Once the base plate was done everything else just fell into place.

    I should also add that you need some other basic skills like drilling, taping, grinding, crushing, and general measuring/layout. I have a background in hardwood floors and cabinetry that helped out a lot.
    #18
  19. TSG59_Steve

    TSG59_Steve Proven Member

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    Wow great write up.
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  20. nukefission

    nukefission Proven Member

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    Nice work, Tim. :)
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  21. the_skin_eater

    the_skin_eater Proven Member

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    Ill add this for an easier time to who-ever wants to try this.

    Dont make the flange by hand...

    You can order them, or, if your cheap like me, have them water-jetted.
    Cost about 30 bucks on average. All you need is a computer drawing of it...

    Though, some people dont have access to it. Perhaps Ill make one and post up.

    I used to sell exhaust flanges for other cars though. Just draw it, send it into a place that does that work, and walaa. Perfect everytime. Im sure though that you can have them draw it for you. they just need measurements.
    This would be the same for any pieces you need holes in as well.

    Like I said, perhaps Ill put one on here for anyone who wants to download. Ill have to measure mine out though...

    Awsome write up though. Looks great.
    #21
  22. peypey's ride

    peypey's ride Proven Member

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    Nice write up! Now that I see how easy this could be, I might just give it a try. I have all the same tools and know how to use them. Plus, my neighbor is a mechanic/welder and has both mig and tig welders in his garage. Have you given any thought to putting a slight angle on the runners, like a slight mendel bend, so that the plenum sits a lil higher? This might save on modding the elbow to tb.
    #22
  23. GreenGSX

    GreenGSX DSM Wiseman

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    When I started this project I didn't think the flange was going to be such a pain. I agree that buying the flange or having one made is the way to go but it was important to prove that I could make every part by myself. If I make another one I'll look into having the flange made. I also agree that if you post a CAD file of the flange it would make it a snap for anybody to walk into a machine shop and have one in hand the same day.
    #23
  24. GreenGSX

    GreenGSX DSM Wiseman

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    I have a bunch of different ideas in my head for adding runner length and different plenum designs but this first manifold I wanted the build to be strait foward and simple. I have a lot of other projects and ideas that didn't start that way and they didn't get finished.

    If I were dead set on longer runners I would just cut the plenum off a stock intake and weld on a bigger one. That's been done before so I don't see it being much harder than building the whole thing from scratch. Another thing to keep in mind is that curved runners are much more expensive and add a whole new layer of complexity to the project.
    #24
  25. black92_tsi_awd

    black92_tsi_awd Proven Member

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    How'd you come up with $50 for materials? Just the box section and tuning would cost that much. Did you not factor in the 1/2" plate you needed.

    Good info by the way and this makes me what to try to make an intake!
    #25

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