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Discussion Starter · #1 · (Edited)
I decided after much deliberation and experimentation to design and build a custom intake manifold that would maximize the advantages of the Holley Sniper 2300 (throttle response, tunability, clean install, etc) and minimize the drawbacks of the the stock Opel Intake manifold design. This project started almost a year ago. Sorry it took so long to get up the first post. This idea is inspired by and builds upon many of the ideas from other posts on OpelGt.Com. I read Rally Bobs article on intake head porting many times. Last summer I learned to TIG weld and modified a spare Opel GT intake manifold in the Rally Bob torquer style. I then spent the rest of the summer porting and proving out the principles in that articles with many iterations using a home built (think shop vac powered) flow bench. I was pleased with performance improvement and wanted more. However, I have come to the conclusion (as Bob did) that there is a law of diminishing returns with the hours put into modifying an intake manifold.

I was also captivated by the Rally Bob post that said
I proved that a few years back when I flow tested a scratch-built intake I made and found 30 CFM per runner compared to a modified stock intake. Across 4 cylinders that is 120 CFM. And each CFM has the potential to make .43 hp. So...51.6 hp higher potential. Shows how restrictive the stock intakes are!
The intent of this project is to go after that horsepower and free the engine from the bottleneck of the intake manifold, in a design that fits under the hood of an Opel GT. So the journey begins, and I decided to build my own intake manifold.

The basic idea is what I am calling a SLANT DRAFT Intake Manifold. The SLANT DRAFT design approach gets rid of the two 90 degrees bends from the stock manifold (one at the bottom of the plenum and one at the elbow of the arms) and replace those with a single long fluid line from the plenum to the intake flange. I also want it to fit under the hood of an Opel GT and retain the heater box. The Holley tech I talked to said that the Sniper could run at any angle, but said that the prime pump (when there is no vacuum, before the car is running) relies on gravity feed, so we agreed that some downward angle is required. My current design has an angle of about 30 degrees.

The idea with the slant draft intake is to to build the slant right into the intake and use the slant to minimize the bends required. The plenum shape I ended up looks kind of like an upside down bird house. That exit angle helps get the runner arms pointing in the right direction. This sort of looks reminiscent of Rally Bob's hammer form mold, but with the plenum tilted forward to keep the profile of the manifold low. So, it is sort of a cross between a down draft and side draft manifold

I went through countless designs in CAD and 3D prints over the course of many months (usually an interation a day). The early CAD drawing below shows roughly the angle of the plenum and the rough path of the runners.

Comfort Human leg Pipe Fashion accessory Auto part

Body jewelry Font Jewellery Circle Symbol





Below is a picture of some early 3D printed components glued together.

View attachment 443711

Plant Automotive tire Boats and boating--Equipment and supplies Tire Road surface

Please let me know if you have other thoughts or design considerations.

Here is some of my other design inspiration.
Rally Bob's Hammer form - This one really got me thinking about smoothing out the constriction in the arms and improvements in plenum flow beyond the V shaped spacer in the bottom of the torquer manifold (which helped a lot).
Wood Musical instrument Countertop Floor House



Another Rally Bob inspiration for this design is from his Project Boom. Here you have the upside down birdhouse inspiration.
Automotive tire Plumbing Gas Automotive exhaust Automotive wheel system




One of the Sci Fi Guy's ponderings helped open up the thinking about running at unconventional angles to keep it under the hood.

Rectangle Font Parallel Slope Pattern
 

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Opeler
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I have a Sniper on my 2.2 engine in my GT paired to a Cannon intake…and you have to have a VERY low profile air filter hat on it to fit it under the hood. Many guys have custom built something out of fiberglass to fit and attach a tube to a remote mounted air filter, like a snorkel style. I worry that you won’t have enough room for the Sniper to fit under the hood with your current design, IF you’re planning on using it in a GT. If not, then I have no clue of the available room in another model of Opel.

Best of luck!

Eric
 

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Very cool!

Nice to see this level of innovation. Glad I could help to inspire it.

I’m told that Ascona/Manta B engine mounts will fit the GT, but are about 1/2” shorter than GT mounts. I’m planning to buy a set for my dad’s turbo GT engine both for added intake manifold clearance and slightly lower CG. This might help your project as well.
 
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Opeler
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I have the Manta B mounts on my Euro 2.4 setup. Using my Cannon intake, along with my intake snorkel on a Sniper 2300, I am barely fitting under the GT hood. The pitch on this prototype intake is too extreme for the GT. If you could merely level the Sniper against the angle of the motor in a GT, you would have a good starting point. If you could drop the initial mounting height for the Sniper, to allow for a spacer, that would be miles ahead of what is currently available.
 

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Opeler
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Here's another thought...Manage the mount height for the Sniper, and the slope the floor of the intake plenum, to facilitate a downhill flow. Doesn't seem like it would take much slope, but anything flowing below level would be an improvement. Beyond that, you are looking at needed hood mods.
 

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I have the Manta B mounts on my Euro 2.4 setup. Using my Cannon intake, along with my intake snorkel on a Sniper 2300, I am barely fitting under the GT hood. The pitch on this prototype intake is too extreme for the GT.
Don’t forget, if you have a high-port head then your intake is already 5/8” higher than the 1.9 head’s.
 
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Opeler
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Yes, I agree that there are differences in the two head types. However, without having measurements, the height of the TBI mount seems to be at least the height, or higher than the height of the intake flange below. We're gonna need a bigger hood bubble.
 

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Looks great I know nothing of clearance in a stock gt (mine being RHD)
I assume after all that great work you had already looked at and ruled out running the centre runners to the outside to even up the intake length?
Just interested to know the rated cfm of the Holley Sniper.
I am following with great interest.
 

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The Young One
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This is a pretty cool idea. I would If you could make something like this for a weber 32/36 or a 38. That would be pretty cool too.
 

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Just Some Dude in Jersey
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I found this calculator for max rpm. In it, it says that our engines' volumetric efficiency is somewhere around 80%:


I also found: "One liter is equal to 61 cubic inches". So:

2 liters = 122 cubic inches

2.4 liters = 146.4 cubic inches

Using the calculator, I came up with this:

2.0 engine cfm's at 6000 rpm and 80% volumetric efficiency:

Rectangle Font Parallel Screenshot Software



2.4 engine cfm's at 6000 rpm and 80% volumetric efficiency:

Rectangle Font Screenshot Software Parallel
 

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Discussion Starter · #14 · (Edited)
Thank you for the support and encouragement. Good thoughts for the watch-outs on the height. I guess what I really need to do now is get all of my aluminum prototype pieces together and tackweld it up. Then, I can remove my current Torquer Manifold and Weber DFAV40 and ensure the fit on the prototype my GT.

Below are a few pictures of an early sand casting of the plenum in aluminum. This was is pretty rough, as I was just learning the foundry work and did not understand the principles very well, so my casting are now much smoother. There is some porosity on the surface, but metal looks pretty clean where I machined it off for the flange. I just received the Holley 2300 flange in the mail from Rally Bob (thank you!). But I will hold off on TIG welding that in place until all of the porting and sanding is done.

This design flows very quiet smooth. I started with the 4 pipes coming in the bottom, then sort of designed it based on what I learned over the summer porting my other intake manifold. I tried to minimize any dead space or sharp edges (except for the small inverted V in the middle to get a clean cut of the air and avoid turbulence). Also, provided for your reference is the size of the plenum next to the stock opel air intake plenum
Headgear Font Mask Circle Pattern
Helmet Automotive design Art Headgear Font
Helmet Jaw Bone Sculpture Art
Automotive tire Synthetic rubber Gas Font Symmetry
 

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Pedal Smasher
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Here is an idea that comes from my own plans for a custom intake manifold. Once you have the prototype design tested for fitment, print it out of a filament that works like casting wax. Then do lost wax casting and just make the whole intake at once. It will come out really nice and only need minor porting and polishing.
 

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Here is an idea that comes from my own plans for a custom intake manifold. Once you have the prototype design tested for fitment, print it out of a filament that works like casting wax. Then do lost wax casting and just make the whole intake at once. It will come out really nice and only need minor porting and polishing.
Sounds good but only polish the outside.
 

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Discussion Starter · #17 · (Edited)
Here are the numbers of the cross sections of this intake design to contemplate. So the round tubes in the arms going to the head flange are slightly larger in cross section area than port openings at the head flange. Any ideas for improvements? It is basically a funnel (narrowest point is the rectangular intake ports on the head). This is different than the stock intake manifold with the narrowest point at the elbow of the arms (compounded by a tight radius turn for bad flow even without doing the computational fluid dynamics). Do you guys think this should flow well like I think it will? Any watch-outs?


Item (in sequence)DimensionsCross Sectional Area
Air Intake (Spectre) Office supplies Automotive lighting Writing implement Rim Auto part
100 mm diameter78.5 cm^2
Holley 2300 Plate (Ralley Bob special) IMG_6050.jpg2 circles at 44.5 mm diameter15.6 cm^2 each
31.1 cm^2 total

I believe the Holley 2300 is rated to flow up to 350 HP
Slant Draft Intake Manifold Outlet Ports Headgear Font Mask Circle Pattern
4 circles at 38 mm diameter each11.3 cm^2 each
45 cm^2 total
Runner Arm air inlets (at plenum) Finger Household hardware Composite material Circle Gas
4 circles at 38 mm diameter each11.3 cm^2 each
45 cm^2 total
Runner Arm Port at head flange Automotive tire Rim Automotive design Auto part Automotive exterior
4 rounded rectangle 28mm x 36mm mm ports10.2 cm^2 each (via CAD)
41 cm^2 total

Here is the Rally Bob quote, that gets what I am going after. Trying to eliminate the intake manifold as the bottlneck.

Oh, and lastly, port-matching the head of a CIH to the manifolds does nothing. Zero, NADA, zip!

The intake manifold is smaller than the intake port openings. So there is no reversion problem there. Making them bigger at the head/ intake junction just adds more volume with zero flow increase. There is absolutely nothing to be gained unless the restrictions in the intake plenum, intake runner radius, and intake ports are corrected first. When those are optimized THEN port matching matters.

It may matter on an old Chevy or a Ford, but on an Opel there is zero airflow gained (flowbench proven) and zero power gained (dyno proven).
 

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The Young One
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Here are the numbers of the cross sections of this intake design to contemplate. So the round tubes in the arms going to the head flange are slightly larger in cross section area than port openings at the head flange. Any ideas for improvements? It is basically a funnel (narrowest point is the rectangular intake ports on the head). This is different than the stock intake manifold with the narrowest point at the elbow of the arms (compounded by a tight radius turn for bad flow even without doing the computational fluid dynamics). Do you guys think this should flow well like I think it will? Any watch-outs?


Item (in sequence)DimensionsCross Sectional Area
Air Intake (Spectre) View attachment 443820 100 mm diameter78.5 cm^2
Holley 2300 Plate (Ralley Bob special) IMG_6050.jpg2 circles at 44.5 mm diameter15.6 cm^2 each
31.1 cm^2 total

I believe the Holley 2300 is rated to flow up to 350 HP
Slant Draft Intake Manifold Outlet Ports View attachment 443821 4 circles at 38 mm diameter each11.3 cm^2 each
45 cm^2 total
Runner Arm air inlets (at plenum) View attachment 443824 4 circles at 38 mm diameter each11.3 cm^2 each
45 cm^2 total
Runner Arm Port at head flange View attachment 443825 4 rounded rectangle 28mm x 36mm mm ports10.2 cm^2 each (via CAD)
41 cm^2 total

Here is the Rally Bob quote, that gets what I am going after. Trying to eliminate the intake manifold as the bottlneck.
Your GT looks pretty nice with that body kit.
 

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Opeler
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725 Posts
Super cool project! I'm running the Sniper 2300 on my 2.6L engine (modified 2.4L core). It has the high port head obviously so clearance is tight. I had to make my own fiberglass hat to go over the top but that all worked out fine. I would LOVE to have a much better performing intake than the one I have now. So I'll be following your work here!
 

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Opeler
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1,624 Posts
Here are the numbers of the cross sections of this intake design to contemplate. So the round tubes in the arms going to the head flange are slightly larger in cross section area than port openings at the head flange. Any ideas for improvements? It is basically a funnel (narrowest point is the rectangular intake ports on the head). This is different than the stock intake manifold with the narrowest point at the elbow of the arms (compounded by a tight radius turn for bad flow even without doing the computational fluid dynamics). Do you guys think this should flow well like I think it will? Any watch-outs?


Item (in sequence)DimensionsCross Sectional Area
Air Intake (Spectre) View attachment 443820 100 mm diameter78.5 cm^2
Holley 2300 Plate (Ralley Bob special) IMG_6050.jpg2 circles at 44.5 mm diameter15.6 cm^2 each
31.1 cm^2 total

I believe the Holley 2300 is rated to flow up to 350 HP
Slant Draft Intake Manifold Outlet Ports View attachment 443821 4 circles at 38 mm diameter each11.3 cm^2 each
45 cm^2 total
Runner Arm air inlets (at plenum) View attachment 443824 4 circles at 38 mm diameter each11.3 cm^2 each
45 cm^2 total
Runner Arm Port at head flange View attachment 443825 4 rounded rectangle 28mm x 36mm mm ports10.2 cm^2 each (via CAD)
41 cm^2 total

Here is the Rally Bob quote, that gets what I am going after. Trying to eliminate the intake manifold as the bottlneck.
I love the whole look of your car! The stance, paint, body mods, the wing and attention to detail are all just right. Good luck on the intake project!

edit:
Did you use a cope and drag casting box to make the pieces? Were you able to get a good foundry sand mixture to use? Could you show us the casting patterns that you used? Just interested in your process, as I dabbled with foundry work in college metallurgy labs many years ago and was really taken by it!
 
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