Idea: Constantly variable ITB trumpets

So I've been thinking of making some variable ITB trumpets. The ones used on the Yamaha R1/R6 aren't constantly variable, it's two sections of tubing that can split apart, so you really only have 2 lengths to choose from. The solution seems simple: Telescoping trumpets. The potential issues are sealing along the telescoping sections, disruption of the airflow where sections meet, and air "bypassing" by leaking out. Any reason this won't work? Has it been done before by any chance?

Only time I have ever seen it executed is with the 26B from Mazda. Mazda does have some ASE white papers floating around that have the math and reasoning behind their designs.

Mazda beat you to it. R26B from the 787B.

If they can make trombone slides that seal consistently (professional musicians are a VERY picky bunch), I would think that it would be completely possible for this type of application too (but of course you probably wouldn't want to make it out of brass).

Ah good. I won't be doing anything with range like the R26B though, not enough room - in fact room might kill my plans entirely.

I thought Porsche had done something similar as well? Or maybe that was another binary approach.

One question I have is whether they really need to seal all that well... I think it's not so much a matter of vacuum/volume as maintaining the pressure wave for reflection. Certainly a perfect seal would be better, as it would presumably weaken the wave to leak at the periphery, but I almost wonder whether avoiding a step in the surface would be more important (e.g. would a diameter change act like the end of the tube and cause a partial reversal/reflection of the wave)...

I could be totally wrong about all that, just something that springs to mind.

More recently, and potentially more relevant, I know Auburn did variable intake runners on their 2012 FSAE car. May be a good starting point if you can get in touch with someone on that team.

In today's computer controlled world, you can just use a linear motor to move the sliding trumpets to any satisfy and combination of RPM or vacuum or vehicle speed or whatever you want.

If you want it to be simple just use a cylinder that adjust against a spring based on vacuum.

I'd go for electronic control, the control system is the easy part IMO.

Have you seen any dyno charts or testing, I know it helps, but I'm wondering to what extent.

For instance see if you can find an engine with ITB's that's been tested with a few different lengths of trumpets and see how big the difference is.

The SR71 Blackbird used variable geometry on the engine inlets. I wanted to refresh my memory an the topic and found...

This awesome SR71 powerplant document

motomoron wrote: The SR71 Blackbird used variable geometry on the engine inlets. I wanted to refresh my memory an the topic and found... This awesome SR71 powerplant document

I think that there are a few (or more) other jets that had different kinds of ramps/flaps/etc to control the airflow into the turbines also (something to do with keeping the compressor from stalling at high speeds I think....
I have read about turbo inlet designs (some with the little 'speed holes' around the inlet) that take compressor stall into account at high intake volumes also).
Kind of interesting stuff, and it seems like it's all kind of related, more or less.

In reply to oldeskewltoy:

That's a hell of a leaky injector. And red-fuel is a huge no-no on public roads

z31maniac wrote: Have you seen any dyno charts or testing, I know it helps, but I'm wondering to what extent.

Well, there's this.

lastsnare wrote: If they can make trombone slides that seal consistently (professional musicians are a VERY picky bunch), I would think that it would be completely possible for this type of application too (but of course you probably wouldn't want to make it out of brass).

but I doubt a trombone needs to deal with the heat, vibration, and long use cycles an engine does

Maybe if for a race only car.. then you could replace the seals daily.. but not for a Road car

Been done on FSE cars a few times. Now how much power you pick up as these your are chasing third and for order harmonics. Cash might be better spent on other things.

motomoron wrote: The SR71 Blackbird used variable geometry on the engine inlets. I wanted to refresh my memory an the topic and found... This awesome SR71 powerplant document

Hell yes.
Was thinking about the Blackbird while mountain biking yesterday.
<3

Just about every jet motor had some kind of arrangement, ISTR that even the Junkers Jumo 004 jet engines in the Me-262 had them.
But it's especially critical for supersonic jets, since airflow changes so much after Mach 1.

z31maniac wrote: Have you seen any dyno charts or testing, I know it helps, but I'm wondering to what extent. For instance see if you can find an engine with ITB's that's been tested with a few different lengths of trumpets and see how big the difference is.

Nothing like those Neon tests, but here's a test of my own. Two sets of runners. Size comparison:

I made two sets of trumpets for my ITB's - one an inch longer than another. I didn't ~feel~ a difference....

SkinnyG wrote: I made two sets of trumpets for my ITB's - one an inch longer than another. I didn't ~feel~ a difference....

You could only feel the difference at certain RPM and you would have to play around with the lengths a lot to find the sweet spot.

My advice is start with some lengths of hose and clamps start as long as you can and work your way down. Measure the differences on the dyno to find the best lengths at the RPM you want.

Or as already suggested you are most likely better off to spend the money elsewhere. Even if you can get it all working right, a long shot, the power gain won't be all that great.

I guess if it's a deal where every last HP counts it might be worth looking into.

The DIY factor will make this much cheaper than any legally imported mods, I'm thinking less than $100US equivalent in total (fabrication of trumpet pieces, heavy duty RC servo). A name-brand cone filter costs more around here. A dude I have to compete with this year blew 15 times as much on a Megasquirt setup alone. If I can get similar gains to that Neon I'd say it's worth it. And since it should offer MPG gains too, with gas close to $8US per gallon it could pay itself off in a few years.

And looking at that Neon's dyno results, I'll want as much range as possible, I was hoping to get away with just 1 telescoping section to keep it simple but it looks like I should get at least 2 (so the length can change by a factor of 3).