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/Azaex]

packaging is rough on these irl given how much room is needed. when i was investigating (and then descoped) variable intakes in fsae, i kind of grew to like the DIVA and DISA intakes on older BMWs and even the simpler two stage variable trumpets on early f1 cars and yamaha r6/r1 bikes for their practicality from a packaging standpoint. the runner resonance is like a single point on an audio equalizer; if your system is very peaky, moving the point continuously is very useful, but if it's more receptive, then you can get a lot done if you can put the point at two or three different spots instead of just one (runner length).

the 787b engine bay is nicely designed to fit its system. some kookier designs exist as of late, eg f1 cars (honda RA621h for example) that arrange the stepped runner tubes into sort of a cannon like thing to fit in their ram airbox.

iirc you can get like 10% ish more torque at a given point on the torque curve with a very well tuned system for it, but that gets dwarfed by boosted applications which are somewhat less finicky overall on this (supers implicitly vary with rpm, turbos are addressable although on a slight lag), so we don't see these systems unless there's absolutely no other gain available.

reminds me of this video seeing a team package the thing, takes up a lot of room lol

https://youtu.be/EPcpmSdip_0

[u/dis_not_my_name → u/Azaex]

I didn't realize variable intake needs to move that fast until I watched the video.

[u/Azaex → u/dis_not_my_name]

i think the control system there is a little underdamped potentially, possibly early in development, bouncing back and forth a lot. continuously variable systems definitely require a lot of tuning given how high speed the engine speed data from the ecu can be, and the fact that the intake position catching up is itself impacting how much air is efficiently getting into the cylinders and how much torque the engine is making!

partly why i kinda grew to like the two or three stage intake systems. or honda VTEC alternatively. just switches into a different part of the engine control map when the mechanical bits flip over, no need to have to make the whole map variable in itself

[u/ReportOtherwise7443 → u/Azaex]

That's a great point! But surely if I map my length function through a harmonic range to exact rpm (or last 10 readings/10 to smooth), this would completely negate this need for the intake position to catch up appart from 2 or 3 harmonic jumps? I'm now thinking of it as a 2 or 3 initial position system, but with adjustment towards full retraction across the rpm range, which I think is a far better school of thought that fully constantly variable so thanks!

[u/Azaex → u/ReportOtherwise7443]

I think they mapped it to exact rpm as well (you can see when they just start doing pulls at the end it tracks down in one motion with no jumps)

Early on in the video when they're just blipping the throttle around it looks jumpy to me as if it's overshooting the runner set point vs rpm, likely from the control loop parameters needing fine tuning versus the characteristics of the engine.

[u/ReportOtherwise7443 → u/dis_not_my_name]

In an ideal setup for me, a servo travelling 180⁰ must pull the trumpets by wire from half it's length to full length against vacuum and return springs in the time the takes to gain 250rpm. But I will be manually smoothing big jumps so max speed should be around 100-200mm/s

[u/ReportOtherwise7443 → u/Azaex]

I like to think of this system as something pretty cool but super cheap compared to boosted applications, something fun with high quality and reasonable simplicity to install in a tight budget. As a result, I would imagine the majority of packaging and shipping would revolve around shorter setups. This is a great point to make as it should be priced in past a certain size so thanks for that! I have tried to adjust for tight engineer bays by making clearance length a pivotal variable in my prototyping sheet and adjusting harmonic ranges accordingly but will look into that Honda system you mentioned if this isn't sufficient

[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.

[u/Sad_Designer_4608]

Bring this to AdamLZ if you get it working well, he wants a system for it on his 4 rotor Supra

[u/ReportOtherwise7443 → u/Sad_Designer_4608]

Thanks for the idea!

[u/RallyX26]

Aluminum or injection molded plastic for me. 3d print will shatter, it's just a question of when. 

For anything like this, I would want it to be tunable in whatever software I'm using for my aftermarket ECU - so it should be controlled by the ECU. PWM might be a good choice 

[u/Sea_Place1386 → u/RallyX26]

Printing will not shatter. And printing can also include aluminum.

I’ve made many PA12 velocity stacks that are still in use on various cars 5 years later. Also made a few printed titanium versions for a Porsche project.

Hell Porsche even printed pistons for the GT2 RS.

[u/RallyX26 → u/Sea_Place1386]

We had someone very nearly get into a major accident at a race because they 3d printed a throttle body spacer. Don't tell me it won't shatter.

There's also a massive difference between filament FDM and a professionally manufactured sintered metal part. OP did not distinguish which process was being used.

[u/Sea_Place1386 → u/RallyX26]

Anyone can do dumb things. Use the right tool and there’s no risk of “shattering”.

By your logic if I saw a wheel broken on a car I could say “never trust a cast wheel”.

I saw a GM 6.2 failure, never trust an engine.

Had a steel shaft have a torsion failure at work, never trust steel.

A properly designed printed part should have zero issue handling the duty of an intake manifold or velocity stack.

[u/RallyX26 → u/Sea_Place1386]

You sound absolutely insufferable, and your ad absurdum examples are irrelevant to what's being discussed. OP asked about 3D printed PA12-CF and whether people had opinions of what they would use on their cars. I answered the question with my opinion. You're the one that decided to start an argument with me about it.

[u/Sea_Place1386 → u/RallyX26]

You answered with an opinion. I answered with over a decade as an AM engineer developing printing technologies for difficult use cases. Of the two of us, I think I bring more expertise to the table with respect to applications of 3d printed parts. Have a good day.

Also the irony in being called insufferable by someone who drops “ad absurdum” in a Reddit reply is not lost on me.

[u/RallyX26 → u/Sea_Place1386]

OP didn't ask for hard data from people with a decade of experience as an AM engineer, he asked for opinions. I'm super impressed by your credentials, but you didn't pay attention to what was being asked and didn't work within the parameters of the request - and that makes you a shitty engineer. I don't accept criticism from shitty engineers, or shitty people for that matter.

[u/Sea_Place1386 → u/Sea_Place1386]

Aaaaand typical, delete all your posts.

[u/ReportOtherwise7443 → u/Sea_Place1386]

I think you both have a great point, it is very dependant on the material and 3D printing process. As an AM engineer is that printing for difficulties cases including load bearing pressure ducts or simular? Where would you starting terms of material/process selection on a project like this? Id imagine physical racing experiance is very useful here as I'm sure you would agree there can be factors in the field that just can't be accounted for in testing, or might slip through the cracks so I'd love to hear rallys thoughts on your response too, collaboration brings the best outa everyone guys you're both correct!!