Variable length runner intake manifold

[pork]

I'm thinking of making a variable length intake manifold for a n/a build

Idea is to have telescopic trumpets on a linear actuator

My question is how would I control the length? Purely rpm based? Vacuum?

Also, once I've figured what signal controls the length, what method of automation would work? Stepper motor, vacuum actuator?

Cheers

[rapidyellow]

how would you ensure a seal on the telescopic part?

[pork]

o-ring in a recess somewhere

All at plannig stage, it's the control side I'm struggling to think of

[SamR380]

Ok, I've bitten, found my research project for the evening.

I assume you're familiar with the Mazda 787B, I found this pretty awesome document about the engine. It's detailed but concise and among other things shows that the manifold length was solely controlled by engine speed:
SAE Document on 787B Engine

It also explains the trumpets are actuated by cable (like a throttle/bicycle brake cable), driven by a dc motor with a potentiometer on the motor for position feedback.

Got a few pics too:


This one kind of shows the winding gear...


and this one the motors (which look like MX5 headlamp motors):

[SamR380]

Oh also, this is a fascinating article for anyone interested in the principles of intake manifold tuning:
Emerald feature on intake trumpets.

[pork]

Yeah, seem s few bits on this.
Cheers for article link

I would of thought it would of been controlled on engine vacuum/load, rather than just rpm

[SamR380]

I suppose it's a bit different for a racing car, it's more than likely to be at full load pretty much all of the time. Maybe on a road car, vac/load/throttle position is more important.

Saying that... if you're after improving the power band perhaps it's not that important until near full throttle anyway. I can't find much research on inlet manifold tuning at part throttle.

I don't know enough about fluid dynamics unfortunately at part throttle does the 'pulse' slow down or is it just reduced in pressure? I'll continue reading...

[swampy76]

The 306 s16 ran something similair only that was done via two inlet tracts per cylinder

[pork]

Quite a few models have 2 inlet tracts, with a butterfly valve opening between the long and short runners.

This idea is for infinitely varying runners

[ChasR]

Ford Duratec 2.5 V6 can also be added to this list. With both runners open they were fairly flat below 3.5kRPM.

[pork]

It would also be easier to construct if the runners were inside a plenum and the throttle pre plenum.....or would it not work, and need to be more like itb's

[Hillmanjames]

the only time you would ever need the increases from a variable intake are when you are driving at what which is why they are all driven from the engine speed Adding the vacuum to the equation would make it considerably more complex to set up ( as well as there is almost no vacuum on an ITB setup after about 20-30% throttle) . Some engines such as the mx5 1.8 with the BP4w head and the bmw M44 engine both have effectively 2 intakes which it switches between at a given RPM.

I've always fancied doing variable length runners but there are two big issues that i have:
1, no car i have ever owned has had enough room to fit them in the engine bay.
2, i don't have my own dyno where i can really dial in the tuning of the engine and at what rate the length changes.

Linear actuators could be used to control the length, I think that these can be set to any given extension, but i'm not sure how fast they extend.


James

[pork]

Would this all work inside a plenum?
With the throttle pre plenum?

[nomad]

^ sam - interesting article by Emerald (brings back memories of pulse lenght tuning and wave harmonics), thanks for that

Once upon a time ... Yamaha bikes (in the 70s / 80s ?) used a resonance chamber in the intake, it might be more practical to add a chamber to each of your intakes and open/close them with a butterfly valve
www.thumpertalk.com/topic/854539-rt-180-intake-air-chamber-what-is-the-purpose/

Should be an interesting project no matter how you decide to do it, pics when done pleeze

[sowen]

If it's of any use I found these when researching my Audi V8 with variable intake





This is what's actually inside the plenum behind the throttle



The flaps are controlled by vacuum actuators on the front side, with what look like electrically controlled solenoids to trigger at different rpms

[pork]

Cool, looks mad,
So it's ok to have trumpet inside the plenum

Il draw some pics of what I have in mind

[pork]

i58.photobucket.com/albums/g240/porkstar5000/Mobile%20Uploads/2015-03/EE1A9CF2-9DFB-48B9-9235-286976A0650C_zpsqfzn9cmy.jpg

[pork]

[pork]

Also what about injector reposition?

Like this?

[reida1994]

the only problem with this is the space in the engine bay. also, i cant remember the angle, but there is a specific angle to get the best performance from the trumpets, so you couldn't just have straight trumpets that slide,