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DIY ITB turbo intake manifold


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For my final project for Advanced Welding, I decided to built an intake manifold out of 6061 aluminum for my old Datsun 280z. I originally planned a individual throttle body project, gathering 6 throttle bodies from a Suzuki GSXR 600. I also planned on building a plenum to support my turbocharged application. The goal was for an all aluminum intake manifold, with a ¾†thick aluminum intake flange, ¼†I.D. aluminum pipe and 6 throttle bodies attached by a silicone or fuel rated rubber hose couplers. This manifold would be attached to a 4†diameter aluminum plenum with 2†velocity stacks with a 2.5†wide bell mouth also attached to the throttle bodies with rated couplers. On paper the project seemed easy, but with every project careful planning was necessary and developed into a harder project then I had imagined.



The first steps in fabricating this manifold required a careful selection of materials, measurements, welding technique and the goal to minimize cost. Welding up runners to a flange for an engine isn’t as simple as cutting a pipe and welding on a throttle body. In a reciprocating engine the intake and exhaust valves are constantly opening and closing. The speed in which the valves open, lift and duration depends on the camshaft design, valve design and engine revolution. As the intake valve opens, the piston sucks air into the cylinder during the induction stroke. Eventually the intake valve closes to allow for combustion of the mixture. The problem lies within the pressure waves created by the closure of the intake valve. When the fast moving air slams into the now closed valve, the air will continue in motion and begin to compress. Now that the air is being compressed the air has nowhere to go. Newton’s First law of motion indicates an object in motion will continue to stay in motion unless an external force is acted upon. Newton’s Third law of motion is for every reaction there is an equal and opposite reaction. This intake wave will revert back down the runner, commonly called a “pulse wave.†Ideally for optimum performance, allowing the pulse wave to bounce back down the runner and enter the cylinder as the intake valve opens will create a supercharger effect. In order to properly time this intake pulse the length of the runner is important, including inside diameter and taper of the runner.




The speed in which these pulse waves travel also varies on the speed of sound, which varies with air temperature, density, humidity and altitude. I was able to find a handy dandy calculator online to provide calculations based off my tube inside diameter, camshaft duration, and peak torque range for my desired RPM. These measurements were for standard conditions at sea level. Now this measurement is not the length of the runner, rather the length from the throttle body or plenum to the center of the intake valve. I was able to calculate with my camshaft duration of 260 degrees and an inside diameter of 1.4†and desired peak torque at 5,350 RPM my runners should be 63†inches long. Ideally this would not work due to space restrictions, so the next best option is to use one of the multiple pulse waves reverted back and forth. My final calculations were 11.2†from the center of the intake valve to the throttle body. This would allow me to take advantage of every 5th intake pulse.




For my parts selection I chose 6061 aluminum which is very light and can be easily welded and cut. I purchased the intake flange from a local member of a car forum I am a member of and began my project. In order to properly weld the aluminum, I needed a TIG machine which is capable of AC or DC current, which I would take advantage of the AC for aluminum. When welding aluminum I would manually select AC current and I adjust the AC wave balance, current in amperage and frequency. The total current adjusted the amount of heat I applied into the material. The AC wave balance adjusts how much the positive or negative waves on the sinusoid wave are applied into the material. Basically the lower the balance value, the less cleaning the arc will provide and deeper penetration into the metal. The greater the balance, the more cleaning is provided but you lose penetration. I chose a 75% balance which is a very nice balance for welding aluminum. Finally the frequency adjusts how wide the arc is on the metal. For a nice wide arc and puddle a low frequency is ideal. The lower the frequency the less penetration I will gain. Increasing the penetration narrows the arc. The narrower the arc, the more focused the heat is, which allows greater penetration. Proper gas and tungsten are also important. For this application I used 100% argon and Zirconiated tungsten.




For cutting the aluminum, I was fortunate enough to use several tools throughout the shop including; a band saw, 14†chop saw with an aluminum rated blade and a plasma cutter. Once everything was cut to my specifications, I was careful to de burr the material and begin the materials for welding. The key to a strong weld with deep penetration and a clean bead is cleanliness. I cleaned the ends of the aluminum with emery cloth, then a stainless steel wire brush and rubbed the aluminum down with acetone to clean off oils and grease. To prevent warping the aluminum flange I clamped the material onto a sturdy welding table with a steel surface to help absorb the heat. The first step was tack welding the runners to the flange to ensure a proper mock up. It is important to add several tack welds around the runner to prevent warping. Once everything was tacked onto the flange, I ran a full fillet bead around the runner onto the flange. This was difficult to do in one continuous run, so I was able to do each runner in 4 sections. My biggest difficulty was between cylinders 1 and 2, as well as 5 and 6. Due to the close proximity of the runners there was a tight gap I needed to weld in. I attempted to use a very small cup and extended the tungsten out to fit the gap, but continued to see a muddy, dirty puddle. This was one of my first errors when welding the project, due to the high air pressure being accelerated out of the smaller cup. My welding instructor mentioned I should lower the air pressure to help out the situation. Unfortunately the gap I was trying to work with was too small and I was unable to get adequate gas coverage. The only option was to apply a lot of heat and filler metal to melt out the impurities in the metal. I would then apply a die grinder to grind out the impurities and apply some more filler metal and heat. Eventually there was clean aluminum grinded down smoothly without pitting or cracks. After welding each runner to the flange I allowed proper cooling to prevent warping or running too much heat on the next runner which could create a uncontrollable weld.




Now that the flange and runners were completed, I temporarily mounted the throttle bodies and came into my second issue of the project. The famous rule, measure twice, cut once should have been followed here. After mounting the manifold in my engine bay I realized I cut my runners too long and did not allow for proper clearance for my plenum. In order to fix this I decided to flip the plenum on top of the throttle bodies and runners and utilize a 180* degree bend. In addition to running out of room, I also already cut the materials for the plenum design which meant I had a 4†diameter pipe now in half horizontally so I did not have a sealed tube. I was able to fix this by re-attaching the 2 half pieces of aluminum and running a full weld down the manifold which wasn’t fairly difficult. I used a square butt joint weld for this application. The next step in welding up this project is cutting the holes for the velocity stacks on the plenum and welding them on. I carefully measured the proper spacing for the velocity stacks to line up with the throttle bodies and used a 2†hole saw on a mill and cut the holes. I was able to insert the velocity stacks from the inside of the pipe and push the attaching end out of the plenum and run tack welds. I learned that polished aluminum is fairly easy to weld once being cleaned properly. I used a fillet weld technique all the way around the velocity stack and plenum. I also extended the length of the plenum by adding a 4†long section of tubing to the end of my plenum using a square butt joint weld.




Overall the project was very difficult due to time constrictions, price and selection of materials, inadequate planning and improper measurements. Fortunately I was successfully able to weld an intake manifold to my specifications and should show an improvement in my engines performance and tuning. Although my poor planning was the primary difficulty, the welding process and instruction by my teacher was extremely beneficial and proved to be much easier than I expected when following procedure and processes.


Anyway.. here are some pics of the project








This above was the original plan. Unfortunately because i did not plan this well enough, I was unable to use this beautiful intake design.
















In the end I was able to use a larger plenum design by flipping the plenum on top of the manifold, similar to a Nissan Maxima intake manifold on the LD28 motor. Yes the rubber hose is ugly... but I am sourcing down a cheaper option than $210 for 6 - 2" u bends! Give me some time!!

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  • 1 year later...

Well it looks like Putfile.com went under..


and I can't edit my post in this section of the forum..


so here are the pics on PhotoBucket.com












** This is the older design.. since this picture was taken, I purchased an aluminum welding kit for my Lincoln 120v MIG. (Thread and pictures here = http://forums.hybridz.org/showthread.php?t=147521&highlight=aluminum+MIG )

I cut the runners down and re angled them to allow the plenum to fit so I don't have to use the 180* degree bend.. plus its super ugly with the rubber hose lol



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