cast aluminum intake manifold

by:AAG     2020-11-05
I started a father and son project a few years ago to build a 1936 Pontiac \"gang car\" street pole for him.
This photo shows a partially completed car that can be driven, there is a completed driving train that only needs the final paint and interior decoration.
I decided to replace the original flat head straight 6 cylinder engine with the Chevrolet 230 cuin straight 6 overhead in honor of the car design.
One feature that I don\'t like about modern engine design is the shared ports of cylinders 1 & 2, 3 & 4 and 5 & 6 in the Siamese inlet and intake manifold.
In the inventory design, these adjacent cylinders are not only not evenly arranged according to the ignition sequence, for the two sets of end cylinders, the intake runner is very long and very short for the two sets of internal cylinders.
In short, the design of the intake system is as bad as possible.
I decided to try and design a custom head/intake manifold for maximum performance and efficiency.
The specification of the required manifold is; -
Cast aluminum for polishing and sturdy. -
6 separate intake channels and 6 isolated ports in the cylinder head. -
\"80 degrees\" design using little Holley 390 4-bbl carburetor. -
Air inlet of equal length. -
At 1800-2000 rpm street cruise speed, runner length with maximum torque is designed.
There are a lot of tools needed for this project because it requires so many disciplines to complete.
There are, among other things, drawing tools, engraving tools, woodworking tools, fiberglass composite building tools, welding tools.
I will not list all the tools in my workshop, but let interested, possibly skilled readers know what tools are used in which step of the project.
The first obvious step is to design the manifold on paper.
What I want is the manifold for street driving, not the competition to decide to design the final specification.
Good intake and in this regard, one of the main principles of the design of the internal combustion engine exhaust manifold is the \"free\" boost of torque, simply the intake valve in the carburetor and cylinder.
There are several common names for this principle;
\"Organ duct\" or \"hemlholtz resenator \".
Its function is like this;
When the intake valve in the cylinder head is opened, there is a negative (vacuum)
When the piston drops in the cylinder, the shock wave generated by the valve seat is sent along the intake channel and the carburetor, trying to breathe in air and gasoline during the next power stroke.
This shock wave travels at the speed of sound in the air.
When the negative wave reaches the full chamber of the effective open space under the carburetor, the second shock wave, which is a positive pressure wave, is sent back to the pipe, towards the intake valve in the cylinder head.
It also travels at the speed of sound, if the runner is the appropriate length of the time required for the length of these two shock wave propagation pipes, the positive pressure wave reaches the valve seat, just as it is closed, \"charge the cylinder\" with additional air/fuel charges to generate more powerful power.
As mentioned earlier, the same principle works on the exhaust side of the engine, but due to the opening of the exhaust valve and the Heat discharged by the piston, the original pressure pulse is positive and the high pressure gas.
The pressure pulse travels along the length of the exhaust pipe, reaches the collector, expands and sends the negative pressure pulse up.
When the exhaust valve is closed, the size of the joint is to make the vacuum pulse reach the exhaust valve.
When the intake valve is just turned on, the cam is designed as the exhaust valve is about to close.
The vacuum pressure pulse actually draws the residue of the exhaust from the cylinder and draws a little intake from the air inlet, effectively boosting the cylinder with more gas.
As the exhaust gas is hotter, the sound speed is much higher and the head tube is longer than the intake tube.
The proper exhaust pipe length of my 2000 rpm Street engine is 34 \"consistent with the length of my 11\" intake pipe.
It sounds like black magic, but it\'s easy to prove to be effective on engine metering machines.
Since the sound speed in the intake runner is 1100ft/sec at a typical air temperature, it is easy to be 1800-
The best speed I want for 2000 rpm is 13 \".
This length is the sum of the intake manifold runner, plus the length of the head air inlet between the manifold flange and the intake valve.
In my case, the dimension is 2 \".
So I need 11 \"for my manifold runner \".
If it all sounds too good, but part of it is true.
The good news is that we get extra power at the design rpm and another complementary boost at the design rpm.
The bad news is that at the speed between these positive values, the power is a little lower than expected, because the negative pressure pulse can reach the valve before closing, resulting in less torque.
Detroit and their friends overseas take a purposeful un approach to designing the manifold
Different sizes of runner lengths are designed for all cylinders, so the power stroke of the cylinder is spread all over the circuit board, which actually smoothed the power curve at a lower level to obtain a \"jet smooth ride \".
With the design of the runner length, I started to write my design on paper.
One thing to consider when designing a casting pattern is that the pattern must be slightly larger than the finished product, because the metal used for the part will shrink when cooling, making the part too small to compensate.
I added a bit of length (
I remember about 1/4)
To the manifold between the far port groups, but other than that, I am not worried about this shrinkage because it has little effect on this project.
I use the same height and width as the head port to adjust the dimensions of the flow channel in the manifold.
I consulted the intake manifold gasket for this size.
The spacing between the port and the mounting bolts was copied from the factory intake manifold.
Carburetor room (
Space volume required to allow organ tube shock wave generation under the carburetor)
It is designed with reference to Holley carburetor.
The picture of my work chart shows how I can implement runners of equal length to all 6 cylinders.
4 cylinders outside are easy.
As long as the pipe runs from the full chamber to the port of the head, the necessary 11 \"will be generated \".
The biggest problem is how to get the necessary 11 \"length in two inner tube runners.
I took advantage of another feature of the organ tube theory.
As long as the bending is smooth and not curved, the resulting pressure wave is not affected by the bending of the pipe.
So by looking at my drawings, you can see how I bent the two inner runners around the intake chamber to get a compact structure while keeping the 11 \"runner length.
The next step is to carve the pattern of the sand casting mold.
I decided to make the pattern in mahogany because it was used by professionals.
It has a very uniform particle with almost no defects, making the molding easy and predictable.
It is also quite hard wood for durability.
I cut the various parts very roughly on the band saw and stuck them together without fasteners.
I am very generous with the profit as I am still a little vague about the final shape of everything.
I\'m much more comfortable working in a 3D environment than working on paper, so this step is actually easier than drawing steps.
The photo of the resulting pattern shows that I created the rounded corners and built the part of the pattern using polyester body putty.
Please note that the highlight extends out to the top of the intake channel and the carburetor mounting flange.
You would expect these to be hollow, and in fact they are hollow in the final product.
On the lower side of the pattern there is a hollow chamber carved there, in the finished manifold, there is an aluminum plate with a gasket and an inlet and outlet with a hot water pipe or pipe to hold the hot exhaust gas used to heat the manifold.
All Street-driven manifold have this heating device to ensure that gasoline from the carburetor evaporates and does not act as a liquid puddle at the bottom of the manifold.
The process of evaporation of liquid gasoline in the carburetor is a heating process, which means that when the liquid evaporates, it absorbs heat, causing the air/fuel to charge and cool, which in turn can re-condense the liquid
Solid and liquid will not burn, only gas will burn.
The car intake system needs to ensure that gasoline is in a gas state inside the engine.
These bumps are intended to accept the end of the gate core used during casting.
The sand casting mold made from the outside of the mahogany pattern is exactly the gap in this shape.
The sand core is not introduced into this cavity to define the flow path and the static pressure box.
The resulting casting will be a huge solid paperweight.
I mentioned that this manifold is a \"80\" degree design.
The manifold designer has several options when deciding which bucket of the multi-channel carburetor is fed.
If the manifold is designed for all the competition, this usually means that the carburetor is in an open throttle state most of the time.
The engine will run at extremely high speeds and all cylinders are trying to get a fair share of fuel.
In this case, the full chamber under the manifold is open or \"Jingdong\", so each cylinder is supplied by each barrel of the carburetor.
This setting is not very effective on the street.
The engine operates at maximum speed and if each carburetor barrel is open to each cylinder, the flow of the air/fuel mixture will be very slow and neither the carburetor nor the cylinder will operate effectively.
In this case, the designer placed a barrier wall under the carburetor to separate the full chamber so that half of the cylinder was supplied by half of the carburetor.
This greatly improves the efficiency at both ends of the system, from low to medium
Range torque and power bring a more enjoyable and fuel-efficient driving experience.
Another ideal feature of the 180 degree manifold is to group the cylinder, so now group the cylinder in order.
Ideally, the cylinder is ignited alternately between two plenary sessions through the ignition sequence.
In this way, the mixture has time to switch between runners at a leisurely pace.
For this engine, runners 1, 2, & 3 and 4, 5, & 6 are the best.
The next step is to make a pattern of sand cores for runners and ventilation rooms inside the intake manifold.
Since these parts have to be installed precisely in the casting mold, leaving an even 1/4 space for the channel wall of the final casting, I used the large mahogany manifold pattern to help make these parts.
I made two and a half of a model with Paris plaster.
Then, as shown in the figure, I systematically lined up each runner with a 1/4 thick modeling clay, which in turn got more pouring of the Paris plaster.
Once hardened, the pieces of each runner are trimmed and massaged until it is exactly the opposite of the desired runner passage.
The next two photos show the runner core pattern simulated on the pattern board, showing the runner\'s appearance inside the manifold.
Imagine that the length of these plaster is actually a hollow tube inside the shell, which is the intake manifold pattern.
Note that the end of each runner extends beyond the extension of the upright plate on the stand.
These extensions are suitable for extensions on the manifold pattern discussed in the previous step.
Pay attention to runner 1 ,.
Group 2, 3 and 4, 5 and 6 together.
Obviously I can\'t cast the manifold with these plaster patterns.
Plaster is solid and hard to get out of the casting, I might want to make multiple manifold so I need to convert these plaster models into patterns to make casting with multiple sets of sand cores.
For these components, I turned to fiberglass-reinforced fiberglass technology.
The last two photos in this section show these fiberglass patterns.
Each pattern is divided into two halves so that they can be separated, removed from the plaster model, and removed from the sand core when made.
With these tools, I can do a lot of manifold.
The sand core looks exactly the same as the plaster model.
Once I have the main patterns and molds for the core, I am ready to take the tools to the local foundry and have them cast my manifold.
This note is not about casting, it is about making patterns for casting, so I will not go into the process of this skill.
I didn\'t make the casting, so we\'re going to leave it to another author with a guiding sense to describe.
As long as there is a free mahogany pattern that doesn\'t help much with my Foundry.
The method of making casting sand type is to make two half of the mold into wooden pattern.
The two molds will then be removed and opened from the pattern.
In this mode, it is easy to lay the sand core made in the previous step into the extended dents made of wood patterns, and the other half of the main sand type is placed on it, resulting in a perfect pipe sink cavity, the molten aluminum can be poured into it.
Two pictures of this step show a glass fiber half
The mold I made with the manifold.
The foundry can place the manifold pattern in this half mold, place the sand of the final casting mold on this half mold of the manifold, then flip it over and remove the fiberglass mold, and hit the sand on the other half of the wooden pattern, let the two halves of the sand mold prepare the core and cast.
I apologize for the very bad picture of the manifold in this step.
I took them flying.
I would have chosen better if I had done so today.
I can\'t take new photos since my son sold his car to pay his first home down payment.
This is a good investment.
Pay attention to the intake channel at the end of the manifold, the carburetor bracket at the top, just like a real manifold!
I drilled several mounting holes using the intake manifold gasket as the guide.
Most of the brackets for this manifold use the lugs that are secured with indirect bolts at the edge of the manifold flange.
The foundry flattened the mounting surface of the manifold and the carburetor surface on a huge grinder they had.
The photo shows that I fixed a commercial carburetor adapter flange bolt to the top of my charger for Holley carburetor.
With these commercial adapters, any carburetor can be used for this manifold.
The last photo shows the manifold on the engine.
The low end torque of this car is very large and you will think it has a V8 engine.
I polish and polish the casting to get the golden effect.
If this is all I have done on this project, it will be in vain.
Although the manifold produces the perfect design, there is still an open cavity in the head between adjacent runners.
Unless these signals are isolated, organ duct signals cannot complete their work.
Attached photos show how I isolated the Port of Siam.
The port identified is the air inlet, and the port on the right in the photo is the air outlet.
The factory isolated the exhaust port, but isolated the air inlet. Go figure.
Please note that the port is divided by the convex part of the head mounting bolt.
I started to separate with brass.
Copper welded steel bars that bring the boss structure to the head surface for all three sets of ports.
I think you can weld this surface to the level of the head if you are a good welder.
I have good luck in copper welding.
These buildings are a little proud of the head surface and have been smoothed out by my local engine workshop.
This will still leave a gap behind the Bolt boss between the inlet valve ports.
To isolate these, I first cut a perforated metal plate with 3/16 holes.
These disks are very suitable in that perimeter.
Then, I started from scratch and built a clay dam in a pair of ports at the bottom, about horizontal with the edge of the Bolt boss.
It doesn\'t matter, fine tune it later.
With the clay dam in place, I poured Devcon liquid steel at the top of the void, which was soaked in perforated steel and poured to the top of the Bolt boss.
Once the liquid steel group (
It\'s an ultra-advanced epoxy resin)
, Removing the clay dam and using my mold grinder and carbide burrs to shape the two ports into perfect shape is a simple taskto-
The organ wave is coming.
Note: only Devcon liquid steel epoxy is used.
Its cost is close to Treasury bonds, but these things are well worth it.
It is recommended for repairing broken engine blocks, manufacturing machine parts, etc.
This is the most impressive epoxy product I have ever seen.
I have no financial interest in Devcon, but I like this product.
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