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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).
Rectangle Font Metal Aluminium Composite material
 

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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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Pedal Smasher
1973 Opel GT
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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.

I'm talking about an intake like this...

I used to stumble across a really pretty intake that Opel designed for 4 cylinder engines, and in chrome it looked really good. But now that I want to find it, I can't. It was better looking than the above intake, very smooth surfaces.

I'm sorry in advance if you're not looking for other opinions on the intake. I just don't see the point in handicapping your design with a carb-esque intake unless you want to run a carb look-a-like TBI for aesthetic reasons. I'll eventually go down the path of designing my own intake for my 2.4 and it will be made for a carb. So, I understand the aesthetic reason being the driving factor. It is at the cost of efficiency in my opinion though. To get the most out of a CIH, a modern EFI system would be needed and Opel circled the same drain with their EFI intakes for many good reasons.
 

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Love the responses to all of the comments! Knowing the limitations of the GT underhood, it is imperative that you keep the highest edge of the Sniper under the center of the hood bubble. The motor will move with revs, and you can fabricate any shape of air intake using fiberglass. If you need a heater, then you are pinned in. I know you are still in R and D, but just food for thought here; if the motor tilts +/- 10 degrees, you might look at a 12 degree pitch on your runners. That will give you a downhill flow and minimize the use of critical space in the area. I will be the first in line if you get this intake to fit. I love the Sniper, but would really like better flow to the head.
 

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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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Pedal Smasher
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Holley sells regular throttle bodies as well as part of their Sniper EFI products. I bet if you were to talk to Holley, they could put together a package for you that you have to put on your own intake. If you have the skills to fabricate your own intake, I bet you have the skills to adapt a Sniper EFI system to a CIH without going the carb-eqsue look, unless that is the look you want. I can't find it now, but Holley used to make a Sniper EFI system that used a more modern V8 plenum that looked similar to the Boss 302 intake. So, they at least used to sell Sniper EFI systems that weren't made to look old school.

I don't know what your budget is, but if you want EFI sidedrafts that is doable. Jenvey EFI side drafts are gorgeous.
 

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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.
Wood Art Composite material Tints and shades Circle
Art Wood Composite material Rectangle Concrete


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.
Sculpture Art Automotive tire Artifact Gas
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!).
Automotive tire Synthetic rubber Rim Artifact Font
Jaw Snout Automotive tire Font Working animal
 

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Opeler
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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).
I would say the Sniper 2300 is hit and miss. It's great when it works and is consistent but like many on the Sniper forums I have issues with consistent idle. Over the winter I sent it back to Holley and they replaced the IAT solenoid. Apparently it was sticking/defective. No cost so hats off to Holley support! It runs better but idle still tries to die when letting off the throttle. It recovers and comes back to proper AFR but frustrating. I have the tuner software and cable and will have to play with that some more. Tried all that last summer with no luck but probably due to the bad IAT.

I can say it's a super easy and convenient way to add EFI to your car. Once all the bugs are worked out it should be great.
 
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Opeler
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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.
Holley does not recommend mounting the Sniper on the side. A few folks have tried but have run into issues. Various details but I agree that would be the best solution. Holley has come out with a few new Sniper offerings since I bought my 2300 including the 1 barrel 175 HP capacity units. If they would come out with a throttle body version of the sniper they would sell tons of them!
 
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Pedal Smasher
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Holley does not recommend mounting the Sniper on the side. A few folks have tried but have run into issues. Various details but I agree that would be the best solution. Holley has come out with a few new Sniper offerings since I bought my 2300 including the 1 barrel 175 HP capacity units. If they would come out with a throttle body version of the sniper they would sell tons of them!
I wasn’t saying to use the Sniper carbs here. The Sniper EFI system has been used with forward facing throttle bodies, like you see on LS and Mod motors. It doesn’t have to use the carb looking TBIs.
 

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Pedal Smasher
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Opeler
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I wasn’t saying to use the Sniper carbs here. The Sniper EFI system has been used with forward facing throttle bodies, like you see on LS and Mod motors. It doesn’t have to use the carb looking TBIs.
That's what I understood you to mean. However what I'm saying is that the Sniper EFI systems are not recommended to be mounted on their sides. I research this quite a bit a year ago or so and no joy. If somebody has successfully mounted the Sniper EFI systems as a side mounted throttle body I would love to see the threads please. Holley makes throttle bodies, yes, but they are not a complete bolt on one-stop system like the Sniper is. All of the Sniper EFI units are downdraft setups.
 

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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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Pedal Smasher
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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.
I need to know this anyways. So unless someone else tells you that distance and the distance from the top of the intake to the bottom of the hood there, I will figure that out tonight.
 

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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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Pedal Smasher
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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?
Rally Bob’s custom intake was made for a carb, I think a Holley 2 barrel. So as long as you plan to use the Holley sniper TBI, then following his intake design is a smart idea.

But if you want to maximize what your engine is capable of, I would either go for a dual side draft setup or use Opel’s EFI intake manifolds. The Holley Sniper TBI is a compromise from the get-go. If you want EFI, direct injection is the best, followed by multi-port injection, and in last place is throttle body injection. It would be pretty hard to add direct injection to a CIH, so multi-port is the best you can do. The Opel EFI intake or dual side draft EFI will get the fuel injected as close to the valves as possible. The problem with TBI’s is that the fuel still can wash down the intake runners. They are still better than a carb but you’re forcing EFI to work like a carb.

It all comes down to what compromises you’re willing to accept. The Sniper EFI has the benefit of simplicity at the expense of not getting the most out of the engine. A better EFI option will likely get more out of the engine, at least in fuel economy, at the expense of a more complicated system in this case. You’re already trying to tackle the issues around a side mounted intake in a tight engine bay. If you only had to worry about airflow and not an air fuel charged mixture, you would have more flexibility with your intake design.

edit I know it may seem like I’m beating the type of EFI issue to death and perhaps I am. I wouldn’t use the Sniper TBI system is I wanted the best EFI option. If I wanted an EFI system that is very easy to install and makes it possible to go back to a carb, then the Holley system is great. My own plans for my 2.4 are to create a custom intake to run a carb, so this thread is very interesting for me. I like seeing what you’re trying to do with that intake. So, the selfish side of me wants to see you pursue this intake design further. But to focus on your own desires, I’d say you need to find a different EFI option if you want to get the most out of your engine. If I really wanted to push the envelope, I’d use Holley EFI components and create a custom EFI system that includes spark control with an Opel EFI intake or a custom intake like it.
 

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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.
 
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