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
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.
Below is a picture of some early 3D printed components glued together.
View attachment 443711
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).
Another Rally Bob inspiration for this design is from his Project Boom. Here you have the upside down birdhouse inspiration.
One of the Sci Fi Guy's ponderings helped open up the thinking about running at unconventional angles to keep it under the hood.
I was also captivated by the Rally Bob post that said
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.
Below is a picture of some early 3D printed components glued together.
View attachment 443711
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).
Another Rally Bob inspiration for this design is from his Project Boom. Here you have the upside down birdhouse inspiration.
One of the Sci Fi Guy's ponderings helped open up the thinking about running at unconventional angles to keep it under the hood.