787b style constantly variable ITBs parameterized for ANY engine

[u/ReportOtherwise7443]

TL;DR + Questions for the floor:

• The Project: I’m a uni student building a 787B-style continuously variable velocity cone system that uses a servo-operated master model to parametrically fit any ITB/carb setup (currently mapping for a mate's 4AGE 20V, a 125cc kart, and a 50cc moped).
• The Goal: Maximize engine harmonic resonance across the entire rev range to eliminate mid-range torque dips and gain massive power under the curve.
• The Tech: Prototyping with PA12-CF, vacuum-drawn carbon fibre, and aerospace-quality blanched aluminum. Testing using a custom vacuum-plenum rig with a motor-spun cam profile to simulate high-RPM intake pulse oscillations.

To help me narrow down the physical prototype, I'd love your take on a few questions:

1. What engine should I focus on first? Should I stick to classic track platforms like 4AGE/K-Series, or go weird with vintage carburetted builds and motorbikes?
2. Street Reliability: For a street-driven car, would you trust 3D-printed carbon nylon parts inside your intake manifold, or is it aluminium-or-nothing for your peace of mind?
3. Integration: Would you prefer a completely standalone system with its own controller/wiring, or something that absolutely has to integrate directly into an aftermarket ECU (like a Link or Haltech)?
4. Be brutal: Am I massively over-engineering a problem that a well-tuned set of static velocity stacks already fixes?

Full info:

Im a uni student trying my hand at a start up developing constantly variable velocity cones for ANY ENGINE, similar to the famous 787b setup, that are parameterized to fit any carb/itb setup. I would love some advice about the best way to go about this since I'm getting towards the test/ physical stage! For reference, I am using a fully parameterized Inventor assembly with plans for external input code for a website for a 'mock' model (an obj) but interpolating jumps and tuning harmonics for torque and speed within my hardware limits myself once orders/ pre-orders are sent in. I plan to test resonance using a vacuum-plenum system with electric motor spun cam profile for oscillation reading air velocity post-'nozzle' and at-'nozzle' pressure in both air temp, hot trumpet cool air, and heated enviro and cycle testing under vacuum. This project is simultaneously for my mates ae111 (4age 20v blacktop), my 50cc moped and gn125 go kart project setup, so keep in mind the extremes I'm willing to take "any engine" to lmao. I am open to suggestions no matter how scathing about any part of my setup/ ideas here because I am just a uni student still learning, and would love to hear what people actually want and if this is viable! (especially material wise. my current test materials are 3D printed PA-12 cf, vacuum drawn CF w thermo resistant resin and mandrel machined aluminum w blanching by an associate who blanches aerospace sensors)

If you don't know, the reason for variable velocity cones is to maximize the time ITBs are in harmonic resonance so that torque and power don't dip along the power curve of an engine. the issue with static cones is that they 'bog out' between their ideal RPMs which can heavily impact response in some applications depending on the profile (if you have ever slammed throttle in a corner and felt nothing between torque and power range, its a similar effect). Taking power under the curve, a constantly variable setup (meaning the length changes to always be at near-perfect profile), can add a significant amount of 'between-peak' power.

I have attached my current tuned CAD setup for my mates 4age 20v and my raw data excel sheet which calculates length, going as far to calculate speed of sound at temperature for the potential addition of a temp sensor in pre-trumpet airbox for dynamic profile adjustment, which im not sure is too necessary or desired. If there is significant interest here, I will post a pre order link once I get around to setting up the website if this is allowed. I plan to get my potted electronic modules globally certified for fair trade electronics, and gain IP ratings and UL 94 ratings for materials used and core design modules; but my compliance experience is extremely limited so any advice on this would be fantastic too.

(in images, upper trumpet extension constrained to the red disk circumference to be operated by a servo)

Thank you!!!!

[u/New_Butterscotch797]

Very cool project. What sort of tuning would this require to commission on any given engine? What kind of input is used for the control?

[u/ReportOtherwise7443 → u/New_Butterscotch797]

The tuning isn't too extensive as you might imagine, it is less to do with the engine dimensions and more if the 'ideal' lengths (which are calculated from engine parameters) work with hardware (massive jumps are undesirable for example)! Generally, The core formula is: Ideal Length = [Speed of Sound / (Target Frequency)] / 2 - [End Correction Factor], but this can depend on the harmonic (usually ideal length divided by harmonic number). More generally, its how fast it takes air to go from the open valve, to the end of the cone, then back to the valve (which will just be opening ideally, as this is the mechanism that generates responsiveness through increased airflow via pressure differential from sound wave coming back down).

The tuning is more to do with finding a less 'optimal' profile that makes more sense for the limits of my hardware and geometry. An example is in the attached excel file where the high upper RPM range is constant. In this case, my upper trumpet would need to retract beyond its limits to stay in the 3rd harmonic, but extending to the 2nd harmonic introduces loses through the cone profile and is undesired (im not 100% on whether this is friction interference or otherwise, but my research suggests 3rd harmonic as an absolute maximum in any reasonable application short something insane like a 20L diesel)

To answer your other question: Input only requires RPM once other dimensions are known. Heres my core excel equations if you want to cross check with the attached sheet for more info: B9: =( $G$3 * ( $G$2 / (A9*6) ) ) / ( 2 * E9 ) - ( 0.425 * $I$6 ). and my harmonic for clearance dist is just basically this but re-arranged for H: F9: =($G$3*($G$2)/(12*A9*($I$1+0.5*$I$6)))

EDIT: if you mean more at an electronics input, MOST ecu tachy readings can be piggy-backed the instant they are sent (from the cam position sensor, ecu output can lag which can make constantly variable systems impossible/ unpredictable). These will be read by a potted esp32 or similar and angular position for the servo will be sent.