variable length intake with ITB's

[Nizm0Zed]

i would imagine if you wanted to do it mechanically, you would use two physical characteristics.

 

Centrifugal force, to drive the setup in relation to engine speed, and engine vacuum to adjust for engine load.

 

as for sealing up the runner tubes, it wouldn't be necessary to do that, as its before the throttle butterfly, so its not metered air.

[Guest TeamNissan]

I'm wondering if there's a way to run something like this in a purely mechanical fashion, using engine vacuum as the governing factor. The first thing that came to mind when I was reading the thread was a sliding sleeve like the ones on the Mazda 767B shown above.

 

The sleeves would have to be pretty lightweight, it may be too much mass to move using engine vacuum. Fiberglass or cf tubes on a common plate(maybe CF with aluminum reinforcements), using a single-acting vacuum piston with a 'draw' stroke(vacuum being applied to the rod side of the piston), working against a return spring. As RPM increases, more vacuum is made, the piston extends further.

 

You wouldn't get the fine control of an electrically governed unit, but if it was done right, you might be able to achieve a similar level of effectiveness.

 

...sealing the sleeve to the walls of the intake to prevent a leak(which would reduce the effectiveness of the variable intake) might be a problem.

 

I just thought the same as I was reading but instead of vac I was thinking gear, maybe off the throttle. As the throttle linkage rotates it can turn a larges single gear moving the set of telescopic trumpets.

 

Vac is a good idea but I really don't think there is going to be enough to pull down on 6+ telescopic trumpets. Plus the trumpets would have to be sprung since 100% mechanical, how else would they return?

 

What about using vac as the signal to a stepper motor though? That way even though its not 100% mechanical you don't have to add a computer just for that. If you don't run a ecu that is, but even if you do it would be much easier for you.

 

I REALLY like this idea and I can't wait to hear more. The more tunable the motor the better imo and I don't think that always means computers.

 

::DISCLAIMER:: I LOVE computers, just saying they seem to fail way more often......

[Guest TeamNissan]

Haha I was just thinking they are starting to actually use variable comp engines outside of labs. Imagine one with variable cam, spark, gate throttle body and variable itb, oy vey. Run it off one computer, with software written for it? lol

[Careless]

I'm wondering if there's a way to run something like this in a purely mechanical fashion, using engine vacuum as the governing factor. The first thing that came to mind when I was reading the thread was a sliding sleeve like the ones on the Mazda 767B shown above.

 

The sleeves would have to be pretty lightweight, it may be too much mass to move using engine vacuum. Fiberglass or cf tubes on a common plate(maybe CF with aluminum reinforcements), using a single-acting vacuum piston with a 'draw' stroke(vacuum being applied to the rod side of the piston), working against a return spring. As RPM increases, more vacuum is made, the piston extends further.

 

You wouldn't get the fine control of an electrically governed unit, but if it was done right, you might be able to achieve a similar level of effectiveness.

 

...sealing the sleeve to the walls of the intake to prevent a leak(which would reduce the effectiveness of the variable intake) might be a problem.

 

I was talking to my father about this, in regards to what would be better... electronic slide rail, electronic screw drive, or mechanical lever action. But I didn't think about the vacuum extension.

 

the problem with the electronic input/ouput is that it has to use TPS or current RPM to determine where it is, and where it should be in its extension.

 

The problem with mechanical lever action is that it's based on pedal position and not engine rotation, which defeats the purpose.

 

The problem with vacuum as i see it, is trying to find a suitable vacuum unit that could do such a thing, and quick enough.

 

Sealing wouldn't be an issue, i'm sure there's a pliable rubber sock that could be oiled and squeezed onto the throttles that would allow it to move enough.

 

How would you do it using vacuum?

 

Raff

[BobbyZ]

Would the actual benefits be noticeable if someone were to make telescoping runners. This is the exact kind of project I have been looking for, electronics are kind of a hobby for me and I think this has some fun design challenges.

 

It would suck though if you spent a few hundred dollars and hundreds of hours designing and building a variable length runner system that had less power than a simple log style manifold... lol

 

I think this would be very doable with my current plan of action for the car. I am going to megasquirt the stock L28, I could easily use Megasquirt to control this kind of system. Maybe not easily, but thats what makes it fun.

 

I guess either way I should probably make my car run first...

[WizardBlack]

You'd want to use a gear and slide system on the runner setup and bi-directional motor with a worm drive gear on it. That way it's not under as much load and won't have to be working when sitting in a particular state (such as just cruising where most cars spend most of the time).

[Guest TeamNissan]

Some fruit for thought. All mazda, 1st is their production version. Last is their stock gate valve set up

[Guest TeamNissan]

Here is the set up on their 787b.

[Careless]

HA! I had a feeling it'd be like a power window motor!

 

It has a cable system and a sealed tube.

 

if the increased width of the powerband actually is improved vastly, then this may be worthwhile... because that looks heavy.

 

 

F**K IT, IM DOIN' IT!

[Careless]

http://inconelracing.com/ seems to have somthing coming up :/

[proxlamus©]

not one link on that inconel site works..

 

its only one fancy picture on that site

[BobbyZ]

What about the length required for lower RPM's. The point of this is that the runner length will be perfectly tuned all across the rev band. But for lower RPM's the runner length gets to be ridiculous. Using one calculation I found, at 1000RPM's you want the runner to be 7 feet long.?????

 

I used the calculation N*L=84000

N=RPM

L=Length (inches)

 

Am i missing something here? (I sure hope so)

 

I guess you could come up with some kind of runner that wraps around itself (think like a trombone...) but then the tuning gets to be a bit more complicated because the runners are no longer straight.

[Challenger]

So your saying (RPM)x(Length)=Length?

 

Proxlamus had an equation that he determined his runner length for his custom intake.

http://forums.hybridz.org/showthread.php?t=126916

[BobbyZ]

No I am saying:

 

(Length) = 84000 / (RPM)

[Careless]

hmmm... it would seem pretty darn long :/

 

perhaps that's why it's easier for these engines to use runners... the lengths are less with higher RPM if the target powerband is in that range.

 

*ponders*

[BobbyZ]

I realized something else too. In order to tune the runner length across the rev band the runner has to cover a huge range of lengths.

 

Using the calculation above (which is close to most of the calculators I found online), if you want the runners to have a range from around 2000RPM to 6000RPM, you would need the runners to move from 42" to 14". I cant for the life of me think of an easy way to do that, you cant just use telescoping runners.

[Guest TeamNissan]

I think your looking at it the wrong way.... for max rpm and in turn cfm you make them as short as possible and work your way longer and down the rpm range until your at the max length and in turn velocity you can fit. Weather that be the wheel well or the back of the air box. Now thats what I think about the teliscoping method... Audi, Benz, BMW, GM, Mazda are ALL using variable set ups on current engines and NONE use the teliscoping method.... For that very reason I assume. If space is a issue then use their method which is a manifold that has the runners wrapped around each other and uses actuated valves to choose air path between dif length runners instead of constantly moving the runners. I posted a pic of both methods above already.

[Nizm0Zed]

the manufacturers have a few reasons for going with those methods,

the 2 main ones are cost in production, and more importantly reliability.

 

looking at the 767B setup, sure its an awesome peice of work, but could you really see it lasting through an average manufacturers warranty? without any problems at all?

 

not so much a prob on one of our cars, because 99% of the people here would have no problems with regular maintenance.

[Careless]

Hear this one guys.

 

The Mazda 787B uses cable motors... chances are they are not stepper driven. Now... is it at all possible that they used some sort of hysteresis control that would extend the runners on throttle input over say....3000 rpm, and retract the runners at.... oh, 5000 rpm or lower with no throttle?

But adding to that, they could have used a butter-fly valve system just as well.... hmmmmm

 

Bob makes a very good point. The lengths are just too long. I think we can gain a GOOD idle, and a GREAT top end for whatever RPM you wish to make power in, but having optimization in both areas is almost unethical with the amount of tubing required.

 

I think the weight savings is a better idea. But, I think the full out throttle extensions would be cool. And a lot easier, as it doesn't need a computer driven speed/distance calculation within the stepper driver.

 

It would just say "oh this guys floorin' it! better get to work!" and extend to make runner length.

 

And then he'll take a back seat when RPM's come down. Perhaps the R26B used this method for reasons we don't know... maybe it had a horribly lumpy idle or it was really difficult for drivers to mozy along at low speed, so they varied runner lengths.

 

I'm up for doing more research if anyone has some good theory on this... This is getting interesting =)

[OlderThanMe]

telescoping intake manifolds???

Just look through the FSAE web sites for much less leaky designs...

There are ways to make a manifold variable than having the runners actually extend and shorten.

If you have a long and a short manifold going to the same cylinder you can creat any length in-between the two lengths by modulating the butterfly on the short runners. Much more reiable/less leaky and it can actually work with boost...

 

I may try to rig something up with my LD28 manifold to be a variable intake for my L26.