ABSTRACT

    To improve the drivability and reliability of my Bugzuki project car I am designing a fuel injection intake manifold for it. Resonate ram tuning will be used to get maximum air flow. I do a lot of freeway driving so I would like a peak in horsepower to come at about 3600 RPM. With the fuel injection system there will be a flexibility built into the fuel system. This flexibility will allow the system to be optimized for power or economy on demand.

    The intake system will be made mostly out of carbon fiber. I found fuel injectors from a 1.3l engine. I will use a 1.5 inch diameter throttle butterfly. There will be a 2.0 liter intake plenum.

Once all the parts are fabricated they will be bonded together, making a complete unit.

INTRODUCTION

    The purpose of this paper is to document the design process and construction of an intake manifold. The manifold will fit a 2001 Suzuki Swift 1.3 liter, 16 valve, 4 cylinder engine.

DESIGN PROCESS

    The original design was to make the manifold fit a 13l, 8v, 4 cylinder Samurai engine. The engine was not setup to be fuel injected. This meant that I would have to design a crank position sensor.

    The goal was to build an intake that would let me drive on the freeway and have a power peak at about 3600 RPM. At 70 MPH the engine is running at 3600 RPM with the current gearing and tire size of the Bugzuki. In order to get this power peak I would need to use Resonate Ram Tuning. There are many formulas, for length verses RPM, but the most commonly used one is:

L = 90000

RPM

90000/3600 = 25inches

In order to verify this number I figured out the calculation through reasoning. Here are the steps that I took to determine intake runner length.

    My calculation came pretty close to the calculation in the previous formula. I think that it is also easier to understand. This satisfied my skepticism for the first formula.

    Most vehicles come with short runners to optimize for high RPM. This would be helpful in my situation because of limited space in the engine compartment. So I considered setting the RAM tuning to the red line of 6500RPM. This would allow me to have runners 13 inches long instead. There is 11 inches from the side of the engine to the fender of the car. 13 inch runners would only require one bend. These runners would be much easier to fabricate. I decided that I would prefer to have the tuning for 3600 RPM.

    I made up an almost complete design of the manifold in Pro-Engineer. The plan was to uses 1.5 inch aluminum tubing. Figure 1 is a representation of the first design.

Figure 1 Intake manifold

    The next set was to determine fuel injector size. I started looking for the formula for fuel flow amounts. Then I determined that it would be much easier to just use injectors from a 1.3l engine. I also figured that is what I would end up doing in the end anyways. I started looking for injectors. I found them at the local parts houses. The problem is that they cost 360 dollars each. That would have put an end to my project. Luckily I found someone on EBay selling an engine with four fuel injector on it. The engine only had 36000 miles on it and it setup for fuel injection for 250 dollars.

    I got the engine. Now with a different engine I needed to redesign the intake manifold. Since I was redesigning I decided to use carbon fiber runners. This would give me the ability to make tapered runners.

    Next I needed to layout the design. I started to make the intake runners. I found it very difficult to make curved and tapered tubes in Catia or Pro-E. In the end I laid out a line representation of the taper sizes. I put these lines at the proper intervals on a 23 in curve. I then laid out a curved line intersecting the ends of the lines. I came out with a drawing of the runner shape I could use to cut it out of foam.

    For this manifold I did not have to design an end plate. It came with one that was already setup to the injectors. I just cut the old manifold off of it. I will bond the intake runners to the plate.

    I went with runners that curve all of the way around the plenum. This required a different plenum shape. I needed to be able to get a 2.0l volume but still get it inside the runners. I opted to go with a D shaped Plenum.

    The taper on the runners went from 2 inches down to 1.25 inches in an oval. Since I was using the taper to get more air flow I determined that I should also use internal velocity stacks in the plenum. Information I found stated a 15 to 19% increase in flow from the use of velocity stacks.

    The main thing I do not like about the new system is that I will have to put the throttle intake at the end of the plenum. The reason for this is that there is not enough room between the runners now. The runners are 3.3 inches apart at the engine. That leaves 1.3 inches between the runners on the top of the plenum, not enough room for a 1.5 inch tube. So the throttle will be on the front side of the plenum chamber. This will probably favor the #1 cylinder. Hopefully the velocity stacks will help distribute the air more evenly.

Construction

    I started the process by making a foam representation of the inside of the intake runners. I used the template that I made to cut out a two inch thick piece of foam. I then carve and sanded, to get the round tube. I then layered it with bondo, to fill the holes and make it firm on the outside. I then spray painted it.

    The idea was to lay up a thin layer of fiberglass over the runner. When it cured I would cut the fiberglass off in two pieces. I would then bond them together and lay up carbon over that. After a lot of talking with the composites lab instructor, we came up with a plan to make a mold of the runner. I could then make destroyable runner molds. I would then be able to make as many internal molds as I needed and keep the original.

    I was going to use plaster to make the internal molds out of. I would then be able to wet the plaster out after I laid up the carbon fiber. I got four different samples of plaster but none of them would wet out after they dried. They had a curing agent in them that reacts with water to seal the plaster. This was a major set back in the progress of my parts. I had spent much time making the mold.

    Then out of the blue I thought of making the molds out of wax. Wax can always be melted back down. This meant that I would just have to reheat the parts after I lay up around the wax. I went to a local craft supply house and got some hard wax that melted at 148 degrees. It is premium grade candle wax. This gives me a good working surface with the ability to melt it out at a low temperature.

    The next obstacle was to learn how to mold wax. I made about six runners that were deformed or broke immediately. I found that a rope down the center gave considerable strength advantages. I also ended up drilling three holes in the fiberglass mold to allow me to pour the wax in with the mold closed. I would pour the mold half full and let it cool some. I would then put in the rope. Then the second half of the mold was put on. Then through the middle hole I would pour in the wax. This let the wax run to the other ends of the mold and spill out when full. I would have to refill the mold a couple times because as the wax cooled it would shrink.

A picture of the first wax piece that worked.

    I then start working on pouring more wax parts. At the same time I started making the first carbon runner. I cut strips of carbon and warped them around the wax mold. After warping the carbon I vacuum bagged the runner to give a better outside finish.

    The next step was to get the wax out of the runner. To do this I found a pan that was big enough to hold the runner. I then put it in an oven at about 200 degrees. After a couple hours the wax was melting out. I was able to grab the rope and pull most of the remaining wax out.

    A problem that I had not anticipated now came up. When the wax came out it got on the outside of the mold. This would make anything that I bonded to the runner break loose. To overcome this issue I put the runner in a bowl of boiling water over night. In the morning most of the residue wax was floating on top of the water. The inside of the runner had also smoothed out quite a lot.

Now I had 1 carbon and 3 wax parts

The next thing I had to do was lay up the other three parts. I did this in the same process as the first part.

I have made up the mold to lay up the internal velocity stacks. These will fit around the outside of the runner where it meets the plenum.

    I made up the stacks on the lathe. I made the small end long to give me room to cut it to the proper length. I also made the large end have a definite spot to cut it to allow a straight cut.

I made four of the stacks so that I could lay the carbon on all of them at the same time.

    I have finished the design of the plenum chamber. It is done in Pro-E. I will make a foam mold of this part. It will be 4 inches in diameter with one side cut off. The sharp edges that are formed, when the cut off is made, will have a radius. The intake ports will be cut into the flat side after the carbon is laid up and cured.

    I should then be able to slide the mold out of the carbon. The carbon plenum will be open on both ends at this point. This will allow access to the inside of the plenum to insert the velocity stacks and runners. After the runners are attached an end cap will be attached to the back side of the plenum. The throttle valve will be attached to the front side of the plenum.

    I will then make holders on the runners to attach the fuel injector to. Some vacuum ports and an EGR port will need to be put into the intake system. These ports will be put in later when the engine control system is designed and exact specifications are determined.

CONCLUSION

    I feel that the project is moving ahead well. I did not get as far as I hope to have gotten. I had to change the design, due to engine changes. I also spent more time on Viking 23 then I had planned at the beginning of the quarter. I feel that I have learned a lot about part design. I see that there are limits to what can be actually made. You can design anything. The implementation of those designs is the part that will make or break the project. If during the design process, the manufacturing process is taken into account, a lot of time can be saved.

    The intake runners that I have made came out pretty good. There are some wrinkles and creases but there are not any visible holes. It looks that they will all be viable parts.

    The plenum design should fit through the center of the runners and slide on nicely. It will give me roughly 2.032 liters of volume inside. This volume is roughly 1.5 times the engine displacement. I have the fuel injectors and throttle body the proper size for this size engine. I should be able to get the engine running smooth with them. I need good low end throttle response with some high end torque.

    Having the velocity stacks and tapered runners should give me good flow into and through the runners. The inside of the runners ended up pretty smooth. I should be able to bond the runners right onto the end plate.

I have enjoyed this project and hope to have a running system soon.

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