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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

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

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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
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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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Discussion Starter · #21 · (Edited)
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.
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.
Don’t forget, if you have a high-port head then your intake is already 5/8” higher than the 1.9 head’s.
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.
For me hood modifications are outside the scope of this project. One of the design criteria is definitely "fits under hood of a GT"

One of the cool things about this design execution is that I built the CAD model based on parametric design. So, the parameters can be tuned and the model adjusts itself. In the original version the plenum is at a 30 degree angle. But if we need more clearance for example, it can be adjusted. I went in the model today and punched in 45 degree angle on the plenum. This parameter along with a few others allows for making it taller or shorter, narrower (to preserve the heater box), etc. It is not quite that simple, but that is the principle. The original execution uses 3 inch center line radius curved 38 mm diameter tubes for the inner ports and a 5 inch center line radius for the outer ports. I was aiming for standard mandrel pipe bender die dimensions, as I had initially planned on making or purchasing mandrel bent 1.75" tube with 1/8" wall, that would give us the 1.5" (38 mm) inner tube diameter. Now, however, I am planning to just use cast the arms out of aluminum. So, I can move away from standard tube radius measurements (one more degree of freedom helps free up the design constraints)! So, all I had to do is redraw the 3D rail that the runner pipe loft follows and voila! Below is the quick rendering / sketch concept from CAD at an angle of 45 degrees . It does not require any changes to the plenum, just printing and cast new arms molds and sand core molds.

Sandal Human leg House Electric blue City


I just finished machining the ports in the head flange on my mini-mill today and drilling the holes for the alignment pins. So, I should be able to test the fit-up in my Opel GT this week. I must say that this hand machining is a lot of work! I can see why Rally Bob used to get these waterjet cut. Batch cutting is the way to go if you need to make a bunch of these. That said, the piece of aluminum only cost $15, and my labor is free. So, I will just chalk it up to therapy (although, not as therapeutic as casting hot molten aluminum).
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Discussion Starter · #22 · (Edited)
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!
Thank you. My dad and I started working on this when I was in high school over 30 years ago. Since the car was in just bad shape (floors completely rusted out etc), we did not know what to do. We discussed for several years to go "Mild" or to go "Wild", we went with the "Wild" approach, since we were not cutting up a fine Opel GT example, but rather saving a badly rusted Minnesota winter car from the junkyard. And, it is a legacy car as it was my Uncle Jack's car who died of cancer.

Did you use a cope and drag casting box to make the pieces?
Yes indeed. You nailed it.

Just interested in your process, as I dabbled with foundry work in college metallurgy labs many years ago and was really taken by it!
I picked up foundry / sand casting work up over Christmas this year. It is a fun and fairly inexpensive and useful hobby that also captured my chemical engineering brain and was propelled by the opel coming down to Georgia where I live now from my dad in Minnesota this past fall.

Happy to share my foundry work, I think I will start another post for this. But will write a few entries in this thread about it. For now, a couple of quick answers.

Were you able to get a good foundry sand mixture to use?
Foundry green sand was too hard to find and too expensive. So, I made my own. I used a 50lb bag of playsand from Home depot for less than $4. I ran that through a 40 mesh screen. Then I bough a 10lb bag of unscented cat litter (bentonite clay) and pulverized it in the Ninja blender. Then, I sifted the clay and added it about 10% by weight to the sand. Then add about 5% by weight water and mixed it up with my power drill to aerate it. It has worked well for me so far. In terms of aluminum, I pick up alloy wheels at a junk yard for about $25. They work great, as they have a good amount (maybe 7%) aluminum silicate (similar to my aluminum TIG filler rod) which decreases the viscosity for casting.

Could you show us the casting patterns that you used?
I am happy to post pictures of the casting patterns. I will post them for the plenum as well as the runner arms casting patter and sand core boxes in subsequent posts in this thread.
 

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Discussion Starter · #23 ·
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!
Wow, that sounds like quite a combination. Do you have any qualitative / directional commentary on the performance? Have you been happy with the sniper? Did you run that engine with a different intake system to gauge the difference?

I have a solid bottom end 1.9 from C&R enterprises from the 80's with butterfly cut pistons, and I believe the autocross cam. We have the 2.0 head with headwork done (stainless steel chevy intake valves). But the car has never breather properly. Now that the electrical sorted out (now getting 14.4 volts from the GM 1 wire alternator), next is the intake manifold and sniper conversion Then, the plan is to bolster up the compression from 8.5:1 to roughly 10.5:1. Then longer term I will be looking for more cubic inches.

So, you are already where I am headed. Do you think the sniper was worth it? One of my aims is going after the sniper is the tunability as I keep changing my engine set up incrementally and would rather tune with data logs, than a box full of jets (which get expensive and I don't yet have an O2 meter).
 

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Discussion Starter · #24 ·
I have a Sniper on my 2.2 engine in my GT paired to a Cannon intake…
Eric
I am jealous of you guys who are already up and running with large displacement strokers for low end torque and the Sniper.

Are you happy with the sniper after living with it a while? Do you have any qualitative / directional commentary on the performance? Did you run that engine with a different intake system to gauge the difference?
 

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Discussion Starter · #27 · (Edited)
If you're wanting to go with something like the Sniper EFI, why not design the intake to have a forward opening like most modern intakes do? This is how the Bosch L-Jetronic systems were designed and I bet those intakes flow pretty nice. Then you don't have to worry about the tight engine bay as much. Unless you want to use a carb look-a-like TBI system.
Well, I guess I am not looking for a sniper EFI per se,as the benefits of the sniper EFI package. I want a snappy throttle response throughout the range of RPM that EFI provides. I like the idea of self learning to get a baseline tune and then the ability to customozeI like the $1000 price point. I like the tidiness of it (ECU, idle air controller, pressure sensor, fuel pressure regulator, etc all built it).

That said, the sniper 2300 is probably not the ideal solution for me. I probably would rather have 2 side draft carbs that were easy to tune (don’t think they exist). Or something like 2 to 4 synchronized Holley side draft Holley EFI port injectors and controller brain (I don’t think they exist).

I like the look and the idea of what you mentioned above. However. I am wondering if it would work as from what I understand the Sniper relies on gravity feed for the prime pump during starting. The intake you posted looks quite cool, but the trunk line seems quite horizontal. Something like that seems like it would be the way to go with a throttle body up front and individual port injectors per cylinder close to the head mounted on a fuel rail. I love that idea, but not sure if I am up to the challenge of building and configuring the required engine management system.

I love the push and am open to exploring other options to get the most performance for price and effort towards unlocking the full potential on my GT without breaking the bank or putting it out of commission for a long time or sacrificing drivability.
 

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Discussion Starter · #30 · (Edited)
Well, I started belt sanding the runner arms for fit on this first all Aluminum version of the SLANT DRAFT prototype. I was pleased that the casting doesn't appear to have a lot of porosity. Here are pictures of the ends of the arms cleaned up with a belt sander.
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Here are a couple of pictures of the rough mock up. Once I finish the fitment, then I will tack weld them together and find out if it fits under the Opel GT hood or not.
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Wood Tool Gas Automotive exterior Machine



And lastly, here you can see the transition from the angled bottom of the plenum to the runner arm of the SLANT DRAFT on the left. I tried to take a similar shot with the stock Opel GT plenum (right) so that you can see the difference in entry angle and and size into the runner arms. I hope it flows nice once it is welded up and ported (if it fits under the hood!).
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Discussion Starter · #36 · (Edited)
The plan is to have the highest edge of the Holley Sniper near the center of the hood bubble, Because of the slanted intake, the air cleaner will be slanted too, and it will be the edge of the air cleaner closest to the engine that will be the highest point. The angles are complex, but from what I can tell so far, the highest point of the intake system at the Sniper is 3.75" beyond the engine block flange (4.25" from the engine block at the intake ports). Or course, the air cleaner would be slanted too. So the advantage is that I only need fractional contribution of the air cleaner height in the Z direction. If the air cleaner is 4" tall, I will only need roughly 82% of that (sin of 90-35 degrees) * 4 = 3.25" and the high edge should extend into the hood bubble.



Question: Does anyone know the offset of the center of the hood bubble from the engine block on an Opel GT? I am only eyeballing it as this stage in the game.

Also, I just checked the height of the stack and the Sniper sitting on the stock GT manifold (with a Holley 2300 adapter plate) which was 220 mm. The linear length of the SLANT DRAFT stack height is longer at 270 mm. But, because of the SLANT, the vertical component of that height was 221 mm at the highest point. I know the SLANT DRAFT design looks taller and in actuality is longer to get the benefit of the elongated, smoothed out flow angles of the runners. But, the extra height is accommodated by the SLANT. The extra height is hidden and tucked away by aligning the stack (manifold + Sniper) to the SLANT / hypotenuse (leveraging the power of the good ole Pythagorean theorem!). 270 mm * sin 55 degrees = 270 mm * 0.82 = 221mm. So, I am hopeful that all of those benefits of the flow design will fit under the Opel GT hood. More to come this week!
 

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Discussion Starter · #38 · (Edited)
why not design the intake to have a forward opening like most modern intakes do? This is how the Bosch L-Jetronic systems were designed and I bet those intakes flow pretty nice
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!
So, that begs the question, what is the ultimate intake system (intake manifold shape + injection system) to maximize the street drivability / power for an Opel GT? Best for me means that the intake is no longer the limiter in the performance of well built street driven CIH engine.That was my intent of building the SLANT DRAFT, but maybe I am barking up the wrong tree. Rally Bob, What were the design characteristics of the aforementioned scratch-built intake? What are some of the best designs you have ever flowed for a streetable Opel GT?
 

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Discussion Starter · #43 ·
The intake in question was a race-only 4-bbl intake I designed and built. I did not even attempt to try to make it fit under the hood, as I had a certain runner diameter, runner length, and plenum volume in mind when I designed it.
Wow, amazing design work and thank you for rounding up and posting the pictures! I cant't decide if I am more excited about the 4-bbl one or the hammer form molds. Thank you for sharing these. Such great inspiration!


Gas Auto part Machine Engineering Metal


So, do you think that something like your high flow 4-barrel carburetor design approach would work well if adapted for Fuel Injection? The thought would be:
1) Place fuel injectors where your nitrous(?) ports are located​
2) Place an an angled air intake where the carburetor goes (this might give it hope to fit under the hood, especially if more like your hammer form approach)​
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3) Place a throttle body in front of the air intake​
4) Appropriate engine management system (have not yet done research on this)​
 

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Discussion Starter · #47 ·
Progress of the day, tackwelded manifold! I have been sanding and working on getting the pieces to align / fit together which is more difficult than you would think with all of the angles. I finally tack welded the arms to the plenum today. Next up is to finish the headflange machine work and tackweld that together too (or I may skip that step), and set it in place in my Opel GT engine bay this weekend!

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Discussion Starter · #49 · (Edited)
Well, I couldn't resist seeing / hearing the difference. I dropped the stock Opel GT intake manifold and the new SLANT DRAFT manifold on my homemade flow bench for a quick round of preliminary data. Initial results are promising from both a pressure drop perspective as well as audibly. I couldn't believe my eyes or ears. The new manifold flows noticably quieter and the pressure drop was less than half! That is a good sign of the smooth flow characteristics hoped for.

I don't have have a fancy flow bench, but here is the data from my un-calibrated shop vac powered homemade flow bench of pressure drop in mm of water. Keep in mind I have not welded on the flanges yet or finished smoothing transitions, so there are likely to be some gains and losses (hopfeully they offset each other). It looks promising to have less than half the pressure drop 13.5mm H20 on the SLANT DRAFT intake vs the benchmark control of 31.5mm of H2O pressure drop on the stock Opel intake manifold.

Pressure drop in mm of H2O
Manifold design
Port 1​
Port 2​
Port 3​
Port 4​
Average​
Stock Opel GT 1.9 Manifold
28​
38​
33​
27​
31.5
SLANT DRAFT manifold
12
14
12
16
13.5

If my memory serves me remember correctly the ideal gas law. PV=nRT. So, pressure is inversely correlated to flow rate. That means, that if we have less than half the pressure drop, there is potential for more than twice the flow. Anyway, definitely encouraging initial data and heading in the right direction.
 

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Discussion Starter · #50 ·
Make sure you bolt the intake tightly to a cylinder head and/or fixture plate. It will warp like crazy when you weld it.
Thank you RallyBob, that tidbit of advice may have saved me countless hours of work! I don't have an extra cylinder head at the moment. But, I might be able to bolt it to a piece of I-beam. Hope that does the trick.
 

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Discussion Starter · #53 · (Edited)
Dual side draft carbs or ITB's are the way to go for maximum streetable power. Especially the ITB's can make a hot cam more civilized and give it a decent idle. A Sprint intake with dual Snipers could be cool, even though it won't make as much power as the dual side draft carbs or ITB's. But it won't probably fit under the hood of a GT.
dual side drafts sound so cool. Just don’t know an easy affordable engine management system oreasy Way to keep carbs tuned.

There was an article I read where they did a comparison between Throttle Body Injection vs Port injection comparison.

They tested a Holley Sniper Throttle Body Injection on an engine that had Individual Port Injection intake manifold but had the Port Injectors off. They tuned it and dynoed it. They Left the Holley Sniper Throttle body on, but turned those injectors off by unwiring them. So, that essentially turned the Holley Sniper into a mechanical throttle body. Then, they wired up the individual port injectors to the same ECU and tuned it to the same air fuel ratios. The individual port injection made about 5 more horse power more than the Sniper Throttle Body injection, on a base of 785 HP.

I know there are so many variables, but that seemed like a pretty good Way to compare.

Full article here
 

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Discussion Starter · #54 · (Edited)
Well, while we’re giving out advice….

I don’t know your TIG welding machine’s capabilities, but given that you are dealing with some thick castings, you will need a lot of amperage to fully weld the intake parts together. My current TIG has no issues with stuff like this, but my first TIG would often overheat and shut down welding thick aluminum.

My solution at that time was to preheat any thick aluminum parts in an old oven I picked up. 450-500 degrees for 20 minutes or so, take the part out and start welding! Aluminum absorbs heat fast but also loses it quickly.

Not only does this help to prevent thermal shutdown, but it makes the welding process go a lot faster too.
Sounds like a good approach. It just might fit in the oven I have in the basement. Thank you for the info. I remember reading it before, but that was a summer ago.I tried that last summer when I was modifying a stock intake manifold in the Rally Bob style torquer style. I only heated it up to 250 or so, but it did make a difference. I think I will give a higher temp a try for a better preheat. Happy to learn the hard earned tricks of the trade. That will save me some time and maximize the time spent welding vs heating up the metal. My welder is decent (225 AMPS), but the torch sure gets too hot to hold and that is what shuts me down (to preserve my hand and save the torch from melting). And it will probably save me some Argon too!

They say that copying is a high form of flattery. So, hope you don't mind that I tried to a machine a Rally Bob style head flange It is not perfect, but should hopefully function as intended. It made a huge difference in trying to get the components to align. I must say, that was a lot of hours of work, but worth it. Sure wish the water jet cut ones were available, but this was a good learning project too. That said, I hope this is the only one I ever have to hand machine. Thank you for the time saved on the Holley 2300 flange!

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Discussion Starter · #57 · (Edited)
Well, I took off my Weber carburetor and tented intake and tried to fit up of the SLANT DRAFT intake. For the most part, the new SLANT DRAFT INTAKE prototype fit, with exception of some interference with the webbing of the 75 Sprint exhaust manifold.
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But the Holley Sniper did not land in the right place. It cleared the fan box area just fine, but it was wrestling with the hood pivot / latch mechanism and it is too far to the passenger side so misses the center of the hood bubble.
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It seems that to align with the center of the hood bubble, the center of the intake needs to be about 8-9 cm inboard of the hood latch.
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Several possible paths forward come to mind…
  1. Shorten the runner arms by 30-40 mm (slice and dice approach)
  2. Refine angle of the arms to gain clearance from hood hatch (belt sander)
  3. Change to 45 degree SLANT (design work, 3D printing, cast new arms)
  4. Try assymetical arms (design work, 3D printing, and cast new arms)
  5. Drop engine height with different motor mounts (rallybob suggestion anticipating this problem earlier in this thread)
  6. Relocate / eliminate passenger side hood pivot / latch. Has anyone done this? I’ll have to search the forum.
  7. Trim the Holley Sniper air cleaner mount surface to prevent interference with hood latch
  8. Switch to the smaller single barrel Holley Sniper auto lite 1100 with centered air cleaner mount
  9. Use SLANT draft intake prototype but switch to port injectors (don't want to go down this path, as I like to drive my car frequently, and designing and getting a custom engine management system could take my Opel GT out of commission for some time)
  10. Make own custom cast aluminum throttle body air inlet hood
Maybe combination of the above will work, else...Install sniper 2300 on current tented intake manifold.

I ordered a few air intake options and will try those and work backwards with what the Sniper position has to be for the hood to close and see what the runners and angles would have to look like to make it work. This is the opposite of where I started (focus on good flow).
 

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Discussion Starter · #59 · (Edited)
I decided to go with a combination of the 1 (trim runners), 2 (refine angles), 6 refine hood latch, and possibly 7 (trim Holley air cleaner base plate). First, I decided to cut at least an inch off of the runners on the head side. This makes more work in terms of porting / blending the flange with the runner, since I cut off the rectangular portion. but worth it, as it should help make the design fit in the Opel GT. So, I broke the tack welds and used painters tape to mark where to cut the runners with the metal bandsaw.
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The shortening of the runners moved the manifold much closer to the right location.
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Then, I re-tack-welded and committed to weld the runner arms to the plenum. I am not a great welder by any means, but made some progress. I had issues with contaminants in the plenum which was made with poor quality aluminum from my early foundry days. So, I really had to crank up the AC balance on the welder for more cleaning action. And I had issues with weird growths on my tungsten. I finally pre-balled my tungsten in advance and that helped. I may be using too small of tungsten (3/32) and could maybe use 1/8” for this high amperage work. And I had issues with the ground on my welder. The runners were made with a much better metal from alloy wheels and better foundry technique. So, that metal welds much better.

Motor vehicle Bone Art Auto part Wood

After a little bit of forum research, it seems that the big hooks on the hood (right side in the picture below) are a safety mechanisms to prevent the hood coming through the windshield during a front collision. The latch on the left seems to be actuated by the hood release cable and the rod rotated to pop up the hood using the offset cam in the middle of the rod. I am thinking about removing / relocating the hooks on the passenger side to accommodate the slant draft air intake.
Trunk Hood Vehicle Bumper Automotive design
 
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