Opel GT Forum banner
41 - 60 of 100 Posts

·
Pedal Smasher
1973 Opel GT
Joined
·
3,441 Posts
It would be cool if a setup like the one below could be figured out.


I’m sure it can be done, to run an inline 4 instead of a V8. Both Edelbrock and Holley create similar parts to figure that out. I haven’t looked into Porsche enough to see if there already are systems like this. But the Porsche and VW crowd would be a good place to look. I know there is CDI systems that can be programmed, I just don’t know if anyone has tied that into EFI yet.
 

·
Super Moderator
Joined
·
14,891 Posts
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?
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.

This one:
Art Snapshot Sculpture Metal Fashion accessory

Gas Motor vehicle Machine Auto part Metal

Automotive engine gasket Gas Auto part Machine Nut



Now, the 2-bbl Weber (or 2-bbl Holley) intake I designed was intended to fit under the hood. It might require plenum modifications (height) depending on the chassis it is fitted to, but there is a lot of flexibility in hammerforming thankfully.

The hammerform I made depicts the INSIDE of the intake, so compared to a stock 2-bbl intake you can see it is much, much larger.

With longer runners (also easily modified for length), a more gentle runner radius, a raised plenum floor, and no 90° sharp turns, there is the potential for higher flow, less air/fuel separation, and improved torque as well as power.
Finger Auto part Personal protective equipment Gas Metal
Wood Gesture Art Artifact Creative arts

Plant Tints and shades Symbol Symmetry Tree

Human body Wood Automotive design Sculpture Tints and shades

Wood Comfort Creative arts Hardwood Thumb

Wood Automotive design Art Artifact Musical instrument
Table Wood Bumper Floor Flooring
 

·
Premium Member
Joined
·
239 Posts
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)​
Office supplies Writing implement Automotive lighting Auto part Metal

3) Place a throttle body in front of the air intake​
4) Appropriate engine management system (have not yet done research on this)​
 

·
Super Moderator
Joined
·
14,891 Posts
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​

I could have easily made the 4-bbl intake 2-2.5” shorter than I made it. I just wanted the greater plenum volume and tunnel ram effect.​

Fuel injectors are generally better closer to the valves for throttle response, so yes, in a location similar to the nitrous injectors would be good.​
 
  • Like
Reactions: GThound

·
Pedal Smasher
1973 Opel GT
Joined
·
3,441 Posts
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)​
View attachment 443996
3) Place a throttle body in front of the air intake​
4) Appropriate engine management system (have not yet done research on this)​
If you still want to go with a carb-esque intake, that is built for multi-port EFI, you should look into Pro M Racing. They created a system that has a carb-like mass air flow meter and throttle body.


The difficult part to the Pro M system is that you would have to work on a custom distributor for it. I don't think they have ever done a 4 cylinder engine. But, if it can be done with their system you would get spark control as well. This is what their throttle body looks like. They use regular injectors and fuel rails still. Oh and I forgot to mention that their software has an open loop component to it, so it's self learning.



I have no idea if this distributor would be compatible with Pro M or Holley EFI systems, but there is a company that has built electronic dizzys for the CIH. I don't know a whole lot about this product though.

 

·
Pedal Smasher
1973 Opel GT
Joined
·
3,441 Posts
I have an answer to the offset measurement question, and it will come with a video. I also have a pretty close dimension from the frame rail by the passenger engine mount to the bottom of the hood bump. That distance is approximately 17 and 5/8 inches, using what I will have to name the peanut butter tape measure method. This video, which I will post soon, is episode 1 of Zeppi’s Garage. Oh and the offset distance is approximately 5 to 5.25 inches from the edge of the valve cover, which is very close to being flush with the edge of the cylinder head. I cover this in the video as well. Unless you’re aiming for insanely tight tolerances, these dimensions should do. If you want insanely tight, you have to edge up to that anyways and gasket thickness becomes a concern even.
 

·
Premium Member
Joined
·
239 Posts
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!

Automotive tire Sculpture Jaw Bone Automotive design
Shoe Wood Beige Automotive design Metal
Automotive tire Art Composite material Artifact Font
Outdoor shoe Bumper Automotive design Auto part Fashion accessory
 

Attachments

·
Super Moderator
Joined
·
14,891 Posts
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!
Make sure you bolt the intake tightly to a cylinder head and/or fixture plate. It will warp like crazy when you weld it.
 
  • Like
Reactions: GThound

·
Premium Member
Joined
·
239 Posts
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.
 

·
Premium Member
Joined
·
239 Posts
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.
 

·
Pedal Smasher
1973 Opel GT
Joined
·
3,441 Posts
I don't have have a fancy flow bench (wish I did at the moment)
I recommend buying David Vizard's book on how to port and flow test cylinder heads. In it, he talks at great lengths about how his crude floating pressure drop flow bench in many ways was a more accurate measurement of how airflow works in an engine. He also talks about how to create a cheap flow bench that will give you useful data for practical, non-pro builds and how to compare that data with a professional flow bench to give you CFM figures. I haven't finished the book yet, as it gets into porting but I've covered the part about flow benches. If you're interested in very technical engine stuff, it's full of useful info. So, don't be surprised how good a cheap DIY flow bench can be.
 

·
Super Moderator
Joined
·
14,891 Posts
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.
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.
 

·
Premium Member
Joined
·
239 Posts
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
 

·
Premium Member
Joined
·
239 Posts
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!

Motor vehicle Bumper Rectangle Font Automotive exterior
 

·
Registered
Joined
·
1,054 Posts
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 inrushes 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
Yes, but that wasn't an individual throttle body intake system with a throttle body for each cylinder.
[/URL]
 

·
Pedal Smasher
1973 Opel GT
Joined
·
3,441 Posts
I finally had time to upload the video to my YouTube channel. Here is the video where I found the clearance distance and offset distance of the teardrop. I needed this information at some point anyways, so I didn't mind figuring it out.

 

·
Premium Member
Joined
·
239 Posts
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.
Vehicle Motor vehicle Automotive tire Hood Automotive exterior


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.
Automotive tire Motor vehicle Gas Audio equipment Auto part


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.
Automotive lighting Hood Light Automotive tire Motor vehicle


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).
 

·
Pedal Smasher
1973 Opel GT
Joined
·
3,441 Posts
You definitely have a bunch of options to figure out where you want to go from here. This thread really makes me wonder how much demand there would be for a turn key EFI kit for the CIH? Especially if it controlled spark and included an intelligent fuel delivery system.
 

·
Premium Member
Joined
·
239 Posts
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.
Asphalt Road surface Electric blue Art Font


The shortening of the runners moved the manifold much closer to the right location.
Motor vehicle Automotive tire Automotive lighting Automotive exterior Automotive design

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
 
41 - 60 of 100 Posts
Top